Q NO 1: A 10-year-old male is brought to the ER with a several day history of high fevers and chills. He also complains of dull pain just above the left knee. There is no joint effusion. X-ray films show soft tissue swelling, bone destruction, and periosteal reaction over the lower end of femur. Which of the following organisms is most likely responsible for this patient’s symptoms?A. Staphylococcus aureusB. Staphylococcus epidermidisC. Streptococcus pyogenesD. Streptococcus agalactiaeE. Streptococcus pneumoniaeF. Streptococcus faecalisG. Moraxella catarrhalisExplanation:Hematogenous osteomyelitis is predominantly a disease of children that mostfrequently affects the long bones. When this condition occurs in adults, it isfrequently due to a predisposition for bacteremia such as IV drug abuse or dialysis.The presenting symptoms of hematogenous osteomyelitis are vague, and anincreased clinical suspicion is required to arrive at the diagnosis. Commonly,symptoms are similar to those of any systemic infection: malaise, fevers and painover one of the long bones. Bone pain is caused by abscess formation within thebone leading to periosteal disruption and bone necrosis. Staphylococcus aureus isimplicated in most cases of acute hematogenous osteomyelitis in otherwise healthychildren.(Choice B) Staphylococcus epidermidis is commonly isolated in cultures due to itsubiquitous nature, and in these cases it is necessary to rule out culturecontamination. S. epidermidis can colonize indwelling intravenous catheters leadingto bacteremia and sepsis, and it can also cause infections of foreign bodies such asprosthetic heart valves and orthopedic hardware.(Choice C) After Staphylococcus aureus, Streptococcus pyogenes (Group AStreptococcus) is isolated from most cases of hematogenous osteomyelitis inchildren. Group A Streptococci are also responsible for streptococcal pharyngitis andskin infections such as impetigo and necrotizing fasciitis. Following either of theseinfections, a patient has the potential to develop rheumatic fever and/or post-streptococcal glomerulonephritis.(Choice D) Streptococcus agalactiae, commonly known as Group B Strep, colonizesthe vagina of young women, and infants born vaginally to colonized mothers canbecome infected. The most common neonatal infections include sepsis, pneumonia,and meningitis. This is the reason for testing expecting mothers for vaginalcolonization with Group B Streptococci and treating those who are colonized shortlyprior to delivery.(Choice E) Streptococcus pneumoniae is the most common etiologic agent ofcommunity-acquired pneumonia. It also causes otitis media in children, sinusitis,meningitis, and sepsis.(Choice F) Streptococcus faecalis is more commonly known as Enterococcus faecalis.Diseases caused by this agent include subacute bacterial endocarditis and urinarytract infections.(Choice C) Moraxella catarrhalis is a part of the normal flora of the upper respiratorytract of healthy adults, children and the elderly. It causes otitis media and sinusitis
in healthy individuals and is commonly responsible for bronchitis and pneumonia inelderly patients with chronic obstructive pulmonary disease.Educational Objective:Hematogenous osteomyelitis most commonly occurs in male children and is mostfrequently caused by Staphylococcus aureus after some bacteremic event.Symptoms are vague and include fever, malaise and pain in the long bones mostfrequently.
Q NO 2: Liver biopsy of a 36-year-old male with a long history of constitutional symptoms stains positive for HBsAg using immunoperoxidase. Which of the following best describes the viral genome replication in this patient’s liver cells?A. One-stranded DNA — Template double-stranded DNA — Progeny one-strandedDNAB. Double-stranded DNA — Template double-stranded DNA — Progeny double-stranded DNAC. Double-stranded DNA —? Template +RNA — Progeny double-stranded DNAD. One-stranded +RNA — Template -RNA — Progeny one-stranded +RNAE. One-stranded +RNA — Template double-stranded DNA — Progeny one-stranded+RNAF. One-stranded -RNA — Template +RNA — Progeny one-stranded -RNAExplanation:A member of the DNA-containing family Hepadnaviridae, the mature hepatitis Bvirus is a spherical double-layered “Dane particle” that has a hexagonal core coveredwith an outer surface envelope of protein, lipid, and carbohydrate. The HBV genomeis a partially double stranded circular DNA molecule, and replication of this genomeis accomplished through a reverse transcriptase DNA polymerase that creates anintermediate + single-stranded RNA template. The progeny of this process is double-stranded DNA.(Choice A) This replicative sequence characterizes parvovirus B19.(Choice B) This replicative sequence characterizes papovavirus, adenovirus,herpesvirus, and poxvirus.(Choice D) This replicative sequence characterizes poliovirus.(Choice E) This replicative sequence characterizes the retroviruses (eg, HIV).(Choice F) This replicative sequence characterizes influenza virus, measles virus, andrabies virus.Educational Objective:The hepatitis B virus replicates via the following sequence: double-stranded DNA —template ±RNA — progeny double-stranded DNA.
Q NO 3: A 34-year-old male presents to clinic with white plaques on his buccal mucosa that were discovered incidentally while brushing his teeth. He is found to be HI V-positive with a CD4+ T lymphocyte count of 280/µL. Two years later, he returns with itching and pain in the perirectal area. Examination shows an ulcerative mass. Which of the following pathogens is most likely responsible for his current condition?A. Herpes simplex virus-2B. CytomegalovirusC. Human papilloma virusD. Epstein-Barr virusE. AdenovirusF. Chlamydia trachomatisG. Candida albicansExplanation:This patient most likely has squamous cell carcinoma of the anus. Anogenitalsquamous cell carcinomas and their proposed precursors, squamous intraepitheliallesions, have been linked to infection with human papilloma virus (HPV)intraepithelial neoplasia of the cervix vulva, penis, and anus have a clear and well-documented association with HPV types 16 and 18. However a definitive correlationbetween HPV and invasive carcinoma has only been established for cervical cancer.Immunodeficiency states (eg, AIDS) increase the host’s susceptibility to HPVinfection. As a consequence HIV infection is associated with a higher incidence ofanogenital carcinomas. HIV-positive homosexual males are more prone todeveloping anal squamous cell carcinoma, and HI V-positive females are more proneto developing cervical squamous cell carcinoma.(Choice A) Although AIDS increases the prevalence of herpes simple x virus type 2(HSV-2) infection and the frequency of symptomatic genital herpes recurrencesHSV-2 is not known to cause anogenital carcinoma.(Choice B) HI V-positive patients who have CD4+ cell counts of less than 100cells/mm3 are at significantly increased risk of developing cytomegalovirus (CMV)infection. CMV most frequently causes retinitis in AIDS patients. Gastrointestinaltract involvement can include esophageal ulcers and colitis. However CMV is notassociated with the development of anogenital carcinoma.(Choices D and G) HIV-positive patients often experience reactivation of latentEpstein-Barr virus (EBV) infection. EBV replication in such patients is associated withlarge cell non-Hodgkin’s lymphomas and oral hairy leukoplakia (OHL). OHL clinicallypresents as single or multiple white plaques on the lateral tongue margins. (Thispatient’s white buccal plaques in contrast are more likely due to candidiasis.) EBV isnot associated with the development of anogenital carcinoma.(Choice E) Adenoviruses can cause severe upper respiratory illnesses pneumoniaand disseminated infection in the immunosuppressed. However these viruses are notassociated with the development of anogenital carcinoma.Educational Objective:Human papilloma virus (HPV) types 16, 18, and 31 are strongly associated with analand cervical squamous cell carcinoma. HIV infection increases the prevalence of HPVinfection and increases the risk of anal carcinoma in HIV positive homosexual males.
Q NO 4: A 24-year-old female presents to your office with burning urination, urgency and frequency. She is sexually active. Urine cultures show catalase- positive, gram-positive cocci. The organism responsible for this patient’s symptoms is most likely to be:A. Coagulase positiveB. HemolyticC. Novobiocin resistantD. DNase positiveE. Yellow pigment producerExplanation:The Staphylococci are Gram-positive cocci that form clusters, pairs and, rarely, shortchains. The catalase test (with 3% hydrogen peroxide) differentiates Streptococci(catalase-negative) from Staphylococci (catalase-positive). The ability to clot bloodplasma (slide and tube coagulase tests) separates Staphylococci into two groups:the coagulase positive Staphylococci which constitutes the most pathogenic speciesStaphylococcus aureus, and coagulase negative staphylococci (CNS) whichconstitutes S. epidermidis, S. Saprophyticus, S. haemolyticus, and 30+ otherspecies. The coagulase-negative staphylococci exist as part of the normal flora onthe skin and in the throat and nose, and only some species can cause infections.S. saprophyticus a common cause of urinary tract infection: itis responsible foralmost half of all UTIs in sexually active young women. S. saprophyticus is resistantto novobiocin. When catalase-positive, coagulase-negative gram- positive cocci inclusters are isolated from urine specimens of the above group of patients thelaboratory performs a novobiocin test to distinguish this organism from other similarpathogens.
(Choice A) Coagulase positivity is a characteristic of S. aureus; this is how S. aureusis differentiated from the other species of Staphylococci that do not expresscoagulase.(Choice B) Hemolysis is a typical feature of Streptococci (streptolysin O andstreptolysin S) and Staphylococcus aureus (hemolysin). S. saprophyticus does notcause hemolysis.(Choice D) DNase is produced by group A streptococcus. DNase degrades DNA inpus to facilitate spread of the organism. Anti DNase can be used as a laboratory testin patients who have had streptococcal infection followed by glomerulonephritis.DNase is not produced by S. saprophyticus.(Choice E) Yellow pigment is produced by Staphylococcus aureus. Staphylococcusmucus usually does not cause urinary tract infections. If S. aureus is cultured fromthe urine you should suspect a metastatic infection from another location in the body(an abscess or infective endocarditis etc.)Educational Objective:S saprophyticus is responsible for almost half of all UTIs in sexually active youngwomen. Staphylococcus saprophyticus belongs to coagulase negative staphylococciand is unique among these because it is resistant to novobiocin.
Q NO 5: An 8-year-old boy is brought to your office with throat pain fever and malaise. Physical examination reveals white exudates on his tonsils and swollen anterior cervical lymph nodes. If the boy returns in a month with fatigue joint pain and chest pain and later in life he develops a heart murmur, which of the following would be the most likely explanation for his condition?A. Protein A-mediated opsonization blockB. Bacterial and human epitope homologyC. Immune complex depositionD. Exotoxin-induced T-cell receptor activationE. Coronary artery aneurysm formationExplanation:The patient described in this question exhibits a clinical picture consistent with acuterheumatic fever as well as long term sequelae of rheumatic fever. Rheumatic fever isa syndrome of fever arthritis, subcutaneous nodules characteristic rash (erythemamarginatum), involuntary rh4hmic movements of the extremities (Sydenhamchorea) and myocarditis leading to valvular in sufficiency of the mitral or aorticvalves. It follows untreated Group A Streptococcal (GAS) pharyngitis. The symptomsof rheumatic fever result from structural homology between antigenic determinants(epitopes) on GAS and on human cardiac CNS and cutaneous tissue (Choice B).(Choice A) Protein A is a cell wall component of Staphylococcus aureus, whichconsists of a single polypeptide chain. This polypeptide chain binds to the Ec portionof lgG causing the epitope binding sites of the lgG to face away from the bacterialcell shielding the cell from complement fixation and phagocytosis. It does not play arole in the pathogenesis of acute rheumatic fever.(Choice C) Immune complex deposition with subsequent complement fixation is thegeneral mechanism behind all Type Ill hypersensitivity reactions. Post-streptococcalglomerulonephritis is a specific example of a Type Ill hypersensitivity reaction.(Choice D) Exotoxin-induced T-cell receptor activation is caused by superantigens.This is the mechanism of action of the toxic-shock syndrome exotoxins produced byboth Staphylococcus aureus and Streptococcus pyogenes. This is not the etiology ofacute rheumatic fever.(Choice E) Coronary artery aneurysm formation is a feared sequela of Kawasakidisease (mucocutaneous lymph node syndrome). Kawasaki disease is a vasculitis ofchildren characterized by high fever palmoplantar erythema with periungualdesquamation, oral mucosal and conjunctival inflammation and cervicallymphadenopathy.Educational Objective:Rheumatic fever is an autoimmune reaction that occurs following untreatedStreptococcus pyogenes (GAS) pharyngitis. Antigenic similarity between bacterialantigens and normal “self” antigens in the heart and CNS are believed to causeformation of anti-self antibodies resulting in RE.
Q NO 6: A 5-year-old male is brought to the ER with somnolence, lethargy and oliguria. He developed diarrhea several days ago that later became frankly bloody. Laboratory studies show elevated blood urea nitrogen and creatinine. Peripheral blood smear reveals fragmented erythrocytes. This patient’s condition is most likely related to consumption of which of the following foods?A. CustardB. MayonnaiseC. Undercooked beefD. Fried riceE. OystersF. EggsG. Canned beansExplanation:Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolyticanemia thrombocytopenia and renal insufficiency. It can occur after gastrointestinalinfection caused by the Escherichia coil strain 0157:H7, a special strain ofenterohemorrhagic E. coil (EHEC). The usual clinical picture associated with EHEC isthat of a hemorrhagic colitis with hemorrhagic diarrhea and severe abdominalcramping caused by EHEC’s ability to secrete a toxin similar to that of Shiga toxin.HUS tends to occur most commonly in children under l0years old and in associationwith treatment of EHEC gastroenteritis with antibiotics.Most cases of HUS associated with EHEC 0157:H7 have been associated with eatingundercooked, contaminated ground beef. Person-to-person contact in families andchildcare centers is also an important mode of transmission. Infection can also occurafter drinking raw unpasteurized milk and after swimming in or drinking sewage-contaminated water. Thoroughly cooking ground beef avoiding unpasteurized milk,and washing hands carefully during food preparation can prevent infection.(Choices A and B) The preformed heat stable enterotoxin of Staphylococcus aureuscan be present most commonly in custard, mayonnaise and processed or saltedmeats and cause food poisoning leading to abdominal cramping, vomiting anddiarrhea. The onset of symptoms is rapid in these cases as the toxin is preformed,and the diarrhea is watery and nonbloody. Symptoms usually resolve within 24hours.(Choice D) Fried rice ingestion followed by gastroenteritis is most commonlyassociated with Bacillus cereus emetic type food poisoning.(Choice E) Consumption of raw oysters is associated with Vibrio Parahaemolyticus(voluminous watery diarrhea, like cholera), Vibrio vulnificus (sepsis with up to a 50%mortality), as well as other Vibrio infections.(Choice F) Raw egg consumption as well as raw chicken consumption and improperfood handling is associated with Salmonella gastroenteritis.(Choice G) Canned beans or any other canned or jarred food can be contaminatedwith Clostridium botulinum, especially if home-canned.Educational Objective:Escherichia coil strain 0157:H7 can cause hemolytic-uremic syndrome (HUS). HUS isa rare condition affecting mostly children under the age of 10. This strain of E. coli ismost commonly contracted after eating undercooked ground beef.
Q NO 7: A 47-year-old male undergoing treatment for chronic myeloid leukemia (CML) complains of headaches and scant nasal discharge. Physical examination reveals tenderness over the paranasal areas. Biopsy of the sinus mucosa reveals the findings below.Which of the following is the most likely cause of this patient’s condition?A. Malassezia furfurB. Microsporum canisC. Rhizopus speciesD. Aspergillus fumigatusE. Candida albicansF. Cryptococcus neoformansG. Blastomyces dermatitidisH. Histoplasma capsulatumI. Coccidioides immitisJ. Sporothrix schenckiiExplanation:The image above shows fungal hyphae branching at acute angles in a V-shapedpattern. This is the characteristic histologic appearance of Aspergillus fumigatus.This fungus is widely distributed in the environment and commonly grows ondecaying vegetables. It is monomorphic, existing only in mold form (withmulticellular hyphae).Aspergillus can cause the following conditions:1. Invasive aspergillosis develops in immunosuppressed patients. The neutropeniaassociated with leukemias and lymphomas is strongly associated with invasiveaspergillosis. The lung is the area most commonly affected. Patients present withhemoptysis and lung granulomas. Aspergillus has a predilection for blood vessels,spreading hematogenously and potentially causing tissue infarcts in the skinparanasal sinuses, kidneys endocardium and brain. Diagnosis is made by lightmicroscopy of tissue specimens, which reveal V shaped, branching septate hyphaeinvading the tissue. Amphotericin B is used to treat invasive aspergillosis.2. Aspergillus can grow in old lung cavities (produced by tuberculosis orbronchiectasis), forming aspergillomas, also called ‘fungus balls.” Fungus balls growinside the cavity only; they do not invade the surrounding lung tissue. Aspergillomascan be surgically removed.3. In patients with asthma Aspergillus can cause allergic bronchopulmonaryaspergillosis (ABPA). Patients present with wheezing and migratory pulmonary
infiltrates. Increased serum IgE and increased titers of antibodies against Aspergillusare characteristic. ABPA is treated with steroids.(Choice C) Rhizopus and Mucor cause mucormycosis. The typical presentation is aparanasal infection in a diabetic patient. Unlike Aspergillus, Mucor and Rhizopus formbroad non-septate hyphae that branch at right angles.(Choices G, H and I) Blastomyces, Histoplasma, and Coccidioides are dimorphicfungi. They grow as molds in nature, but exist in the human body in yeast form.Thus, there would not be hyphae seen in biopsy specimens.(Choice E) Candida albicans is a component of normal human mucous membraneflora. On light microscopy, it appears as oval budding yeast and pseudhyphae.(Pseudhyphae are not true hyphae; rather, they are formed by elongated yeast.)(Choice F) Cryptococcus neoformans causes meningitis and lung infections in AIDSpatients. It is an oval budding yeast with a thick capsule. India ink stain of the CSFreveals a wide clear zone around the nucleus (corresponds to unstained capsule).Educational Objective:Neutropenic patients are at risk for infection with Aspergillus fumigatus. This fungusproduces septate hyphae with V shaped branching. It causes invasive aspergillosis,aspergillomas and allergic pulmonary aspergillosis (ABPA).
Q NO 8: An 8-year-old male who recently moved to the United States from Asia is brought to the emergency room with throat pain and difficulty breathing. Soon after being admitted to the hospital, he dies of severe heart failure. In the laboratory, bacterial isolates from this patient’s tonsils are found to cause rapid death of 8 out of 10 exposed guinea pigs. Two of the 10 experimental animals survive. The surviving animals most likely possess which of the following antibodies?A. IgA against adhesion proteinsB. Opsonizing 1gMC. Complement-fixing 1gMD. Immobilizing lgGE. lgG against circulating proteinsExplanation:Diphtheria is an acute bacterial disease that is rare in the United States due towidespread administration of the Diphtheria-Pertussis-Tetanus (DPT) childhoodvaccine. The DPT vaccine contains diphtheria toxoid, which stimulates production ofneutralizing antibodies against the binding component (B subunit) of the diphtheriaexotoxin. Antibody binding prevents the exotoxin from attaching to host cellmembrane receptors, thus preventing disease (choice E).Corynebacterium diphtheriae colonizes the or oropharynx of non-immunized childrenand can cause pharyngitis. Patients may have a dark pseudomembrane in theposterior pharynx (composed of C. diphtheriae bacteria leukocytes, fibrin andnecrotic mucosal epithelial cells) on physical exam. This pseudomembrane ischaracteristically tightly adherent and will cause bleeding if avulsed.The bacteria, however, are not the direct cause of the major clinical sequelae ofdiphtheria; instead, it is the C. diphtheriae exotoxin that exerts these effects.Exotoxin is released into the bloodstream and deactivates elongation factor-2(EF-2),a protein that facilitates the movement of the forming peptide chain on the humanribosome. This effectively inhibits human protein synthesis. The clinical consequenceis cardiac and neural toxicity resulting in cardiomyopathy and heart failure as well asneuropathy, paralysis, coma and death in 10% of patients.(Choice A) IgA is the primary immunoglobulin found on mucosal surfaces and insecretions. C. diphtheriae expresses K antigen, an antiphagocytic molecule, on itscell wall. This allows the organism to colonize the posterior pharynx and produceexotoxin despite the action of IgA. (Choices B and C) Disease caused by C.diphtheriae is not due to bacterial invasion of the host; rather, it is due to circulatingexotoxin. Neither 1gM opsonization nor complement fixation would affect circulatingexotoxin, thus neither would prevent the development of severe disease and death.(Choice D) Corynebacteria are nonmotile organisms, so an immobilizing antibodywould not be relevant here. Furthermore, C. diphtheriae causes disease via itsexotoxin, which would not be affected by an immobilizing lgG.Educational Objective:C. diphtheriae causes diphtheria, an acute bacterial disease that initially affects theoropharynx. The organism is spread by respiratory droplet trans mission and causesdisease via its AB exotoxin. The B (think: binding) subunit allows penetration of theA (think: active) subunit into the cell, to inhibit ribosome function. Neural andcardiac toxicity are serious potential sequelae. Immunization with the diphtheriatoxoid induces production of circulating lgG against the exotoxin B subunit,effectively preventing disease.
Q NO 9: CSF cultures from a neonate with fever and poor feeding reveal motile Gram-negative rods that form pink colonies on MacConkey agar. Which of the following is the most important bacterial factor in the development of this infection?A. CapsuleB. VerotoxinC. antigenD. Fimbrial antigenE. Lipid AExplanation:The neonate in the above vignette suffers from meningitis secondary to an E. coilinfection. E. coil is a motile gram- negative bacillus that is facultatively anaerobicand able to ferment both lactose and glucose. It grows well on blood, MacConkey,and eosin methylene blue (EMB) agar plates. MacConkey agar is a selective anddifferential medium used to isolate gram-negative organisms from contaminants inclinical specimens. When an organism ferments lactose on MacConkey agar, thelocal drop in pH causes the colony to take on a pink-red appearance. The bile saltspresent in MacConkey agar prevent the growth of Gram-positive organisms;therefore any CSF culture showing growth on MacConkey agar implies CNS infectionwith enteric bacteria—specifically, infection by E. coil.Group B Streptococcus is the most common cause of neonatal meningitis in theUnited States, followed by E. coil Listeria monocytogenes, and Klebsiellapneumoniae. Hemophilus influences type b also remains an important cause ofmeningitis in non immunized infants.The K-1 capsular antigen is present in 20-40% of intestinal E. coil isolates. E. coilcan invade the blood stream of infants from the nasopharynx or GI tract and canthen travel hematogenously to the meninges. The K-i antigen is considered themajor determinant of virulence among strains of E. coil that cause neonatalmeningitis. The K-1 antigen inhibits complement phagocytosis, and other hostresponses. The capsule is immunogenic and anti capsular antibodies are protective.(Choice B) Verotoxin is another name for the shiga-like toxin synthesized byenterohemorrhagic E. coil (EHEC). Exotoxin expression is not present in any of thepathogens commonly associated with neonatal meningitis.(Choice C) The O antigen is simply a cell wall outer membrane polysaccharideantigen used to classify gram- negative bacteria.(Choice D) Fimbriae, or pili, are a virulence factor that allows bacteria to adhere tothe target tissue thereby establishing infection. Examples of organisms that use piliare Neisseria is meningitidis, uropathogenic and diarrheogenic E. coil and Vibriocholerae.(Choice E) The Lipid A in LPS is similar for all enterobacteria; Lipid A causesactivation of macrophages, which leads to widespread release of IL-i and TNF-alpha,which in turn cause the signs and symptoms of septic shock.Educational Objective:E. coli is a frequent cause of neonatal meningitis second only to Group BStreptococci (GBS). The capsule synthesized by some E. coil (K-1 antigen) is avirulence factor that allows the bacteria to survive hematogenous spread and toestablish meningeal infection. Most strains of E. coil causing neonatal meningitis dopossess this K-1 antigen.
Q NO 10: A 24-year-old male presents to your office with an extremely painful vesicular rash on the shaft of his penis. He has never had such symptoms before. Tzanck smear of the lesion is positive for multinucleated giant cells. The lesion heals in ten days without any treatment but reappears two months later. Which of the following had the greatest potential to prevent a recurrence of this patient’s condition?A. Regular condom use after the first episodeB. Short course of acyclovir during the first episodeC. Immunoglobulin during the first episodeD. Daily valacyclovir after the first episodeE. Daily lamivudine after the first episodeExplanation:This previously asymptomatic patient’s new vesicular rash and positive Tzancksmear are consistent with a primary genital herpes infection. Most herpes infectionsbelow the waist are caused byHSV-2 and occur due to reactivation of latent infectionwithin the 3-2. 3-3, and 3-4 dorsal root (sensory) ganglia. Recurrence of genitalherpes can be suppressed or minimized with daily oral valacyclovir, acyclovir, orfamciclovir. Such suppressive therapy can reduce the number of clinical recurrencesby approximately 50% and the number of viral culture-positive recurrences by up to70%.(Choice A) Although condom use may prevent transmission of HSV-2 to a sexualpartner, it does not reduce the frequency with which HSV-2 genital herpes recurs inthe host. Condom use might have prevented this patient from acquiring his primarygenital HSV-2 infection, however.(Choice B) Acyclovir treatment during a primary herpetic episode usually reduces theduration of viral shedding time for lesional healing constitutional symptoms and localpain. However treatment with oral acyclovir for 7 to 10 days during the primaryherpetic infection does not appear to alter viral latency or recurrence.(Choice C) Immunoglobulin therapy is not commonly used for genital herpes simplexinfections. Such therapy can be used to combat varicella-zoster infections inimmunocompromised individuals, in neonates whose mothers developed a perinatalvaricella infection and as prophylaxis in pregnant females exposed to varicella.(Choice E) Lamivudine is a nucleoside analog reverse transcriptase inhibitor activeagainst HIV-1 and HIV-2. It also has some activity against hepatitis B virus but isnot known to be effective against HSV-2.Educational Objective:The combination of new onset genital vesicular rash with a positive Tzanck smear ina previously asymptomatic patient is suggestive of prima genital herpes due to HSV-2. Recurrences of genital herpes can be reduced through daily treatment with oralvalacyclovir, acyclovir, or famciclovir; these drugs suppress reactivation of latentHSV infection. Condom use can help prevent a prima genital HSV infection but doesnot prevent reactivation of latent infection.
Q NO 11: A group of investigators is trying to develop an anti-gonococcal vaccine. Their attempts to use pilus components to induce long-lasting immunity would most likely fail because of:A. Antigenic mimicryB. Low molecular weightC. Non-protein structureD. Antigenic variationE. Local immunosuppressionExplanation:N. gonorrhoeae have pili which are hair-like protein polymers that project from thesurface of the cell and are involved in the attachment of the organism to mucosalsurfaces. Those gonococci that have pili are able to adhere to susceptible cells andthereby begin the infectious process. When the host produces antibodies directedagainst gonococcal pili, adherence to the mucosa is inhibited. In a given strain at agiven time, only a single pilus gene is functional, so only one pilus type is expressed,but the pilus genes are known to undergo antigenic variation at a high frequency.Antigenic variation is a process by which the structural genes for pilus proteinsundergo recombination with each other to produce new antigenic types of pili, andthe array of different antigenic pilus types produced by this mechanism theoreticallymay be quite large. This diversity of pilus protein expression is one reason whydevelopment of an effective vaccine directed against the gonococcal pilus is sochallenging.(Choice A) Antigenic mimicry is the sharing of antigenic sequences between themicroorganism and the host cell, thus leading to autoimmune disease if the hostmounts an immune response against the infectious epitope and that epitope hassufficient sequence homology with a host antigen.(Choice B) Pilin proteins do not represent a low molecular weight structure thatwould be poorly immunogenic.(Choice C) “Non-protein structures” does not describe pili as gonococcal pili areprotein polymers. This statement is also incorrect because vaccines have beendeveloped against non-protein structures. The meningococcal and the pneumococcalvaccines are both examples of polysaccharide vaccines used in clinical practice.(Choice E) Local immunosuppression does not describe a potential failure forvaccination. Immunosuppression can blunt the effect of a vaccine to induce anadequate antibody response requiring multiple inoculations in order to induceimmunity. This is the case in patients chronically immunosuppressed withcorticosteroids. Often after vaccination they will develop sufficient immunity, butantibody titers should be checked to be sure.Educational Objective:The gonococci use their pili to mediate adherence to the mucosal epithelium. Anantibody against the specific pilus protein expressed by a gonococcus would preventmucosal adherence and initiation of infection, but each gonococcus possesses theability to modify the pilus protein that it expresses by the process of antigenicvariation and thus avoid host defense to some degree as well as make vaccinationdirected against the pilus protein difficult.
Q NO 12: A 34-year-old male is hospitalized with difficulty swallowing and blurred vision of sudden onset. He has never had symptoms like this before. Routine nerve stimulation studies show normal nerve conduction velocity but decreased compound muscle action potential. The patient should be carefully questioned about:A. Missed vaccinationsB. Recent travelC. Unprotected sexual contactsD. Home-canned food consumptionE. Family historyF. Recent antibiotic useExplanation:Botulism is a rare but serious paracytic illness caused by a nerve toxin produced bythe bacterium Clostridium botulinum. There are three main types of botulism. Food-borne botulism results when an individual eats foods containing the botulism toxin.Wound botulism is the result of toxin production in a wound infected with C.botulinum. Infant botulism occurs when a baby consumes C. botulinum spores whichthen mature into vegetative toxin-producing cells in the intestine. (Contaminatedhoney is a frequent cause of infant botulism.) All forms of botulism can be fatal andare considered medical emergencies.Botulinum neurotoxin is among the most toxic substances known. The anaerobicenvironment within a can of food contaminated by C. botulinum spores allows sporegermination and organism growth. The botulinum toxin produced by the vegetativeC. botulinum bacteria remains intracellular until autolysis releases the potentneurotoxin into the food. (This toxin IS NOT actively secreted by the bacteria.) Thetoxin is readily destroyed by heating but if food containing the pre-formedneurotoxin is not cooked well the toxin will be able to exert its effects. The mostcommon clinical manifestations are diplopia, dysphagia and dysphonia (three ‘Ds’),which occur within 12-46 hours of neurotoxin consumption.(Choice A) There is no vaccine against botulism. Botulism is treated with antitoxinthat blocks the action of circulating toxin. However, the antitoxin is unable toinactivate toxin that has already gained access to nerve cells. Botulism is furthertreated with supportive measures like intubation and mechanical ventilation fordiaphragmatic paralysis.(Choice B) Recent travel is associated with numerous diseases including infectiousdiarrhea, malaria, hepatitis, yellow fever, dengue fever and Hantavirus. Botulism isnot associated with travel, but obviously food can be improperly prepared or storedin any country.(Choice C) Unprotected sexual contacts invite sexually transmitted diseases. STDsare caused by bacteria (Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasmahominis, Ureaplasma, urealyticum, Treponema pallidum, and Hemophilus ducreyi),viruses (HIVI HSVI Hepatitis B, HPV) and protozoans (Trichomonas vaginalis).(Choice E) A family history of recurrent infections can suggest a heritableimmunodeficiency such as X-linked agammaglobulinemia of Bruton or Wiskott-Aldrich syndrome. Botulism is a toxin-mediated disease, not an organism- mediateddisease, so immunodeficiency would not predispose to it.(Choice F) Recent antibiotic use can upset the intestinal bacterial balance, allowingthe multiplication of Clostridium difficile in C. difficile colitis. Antibiotics can alsodisturb the vaginal flora, predisposing to vaginal candidiasis.
Educational Objective:There are three main kinds of botulism: food-borne botulism, wound botulism andinfant botulism. In food-borne botulism, botulinum neurotoxin in food (produced bythe organism Clostridium botulinum) prevents release of acetylcholine from nerveterminals at the neuromuscular junction, thereby preventing muscular contraction.
Q NO 13: A 34-year-old female who suffers from bronchial asthma is found to have recurrent transient pulmonary infiltrates. Complete blood count shows eosinophilia. A chest CT scan reveals proximal bronchiectasis. This patient’s condition is most likely related to colonization with:A. Pseudomonas aeruginosaB. Streptococcus pneumoniaeC. Legionella pneumophilaD. AdenovirusE. Aspergillus fumigatusF. Strongyloides stercoralisExplanation:Aspergillus fumigatus is a low virulence fungus that generally does not causesignificant infections except in immunocompromised or debilitated patients. It may,however, colonize the bronchial mucosa and complicate asthma or cystic fibrosis viaa hypersensitivity reaction. The result is allergic bronchopulmonary aspergillosis(ABPA). ABPA occurs in 5% to 10% of steroid-dependent asthmatics. Patients withthis condition have very high serum IgE levels, eosinophilia, and IgE plus lgG serumantibodies to Aspergillus. There is intense airway inflammation and mucus pluggingwith exacerbations and remissions. Repeated exacerbations may produce transientpulmonary infiltrates and proximal bronchi ectasis.(Choice A) Pseudomonas aeruginosa is an opportunistic aerobic Gram-negativebacillus that is a frequent, sometimes deadly, pulmonary pathogen in patients withcystic fibrosis or neutropenia.(Choice B) Although asthma may be a risk factor for the development ofpneumococcal lung colonization and pneumonia pneumococcal disease generallyresults in resolution with preservation of lung lobular architecture. Potentialcomplications of pneumococcal bronchopneumonia or lobar pneumonia include lungabscess, empyema, or lung fibrosis. Bronchiectasis is not a common outcome ofpneumococcal pulmonary disease.(Choice C) Asthmatics do not have a predisposition to lung colonization withLegionella.(Choice D) Although viral respiratory infections can cause asthma exacerbations andadenovirus colonization of the lung may be associated with asthma chronicity, pureviral pneumonias do not progress to bronchiectasis.(Choice F) Strongyloidiasis can cause pulmonary symptoms including cough,asthma-like bronchospasm, and hemoptysis. It can also produce a transientpneumonia as larvae migrate through the lungs on their way to the laryngopharynx.In rare cases, chronic lung involvement may cause features of obstructive and/orrestrictive pulmonary disease. Progression to bronchiectasis is not commonlyreported.Educational Objective:Allergic bronchopulmonary aspergillosis (ABPA) due to Aspergillus fumigatus maycomplicate asthma. ABPA can result in transient recurrent pulmonary infiltrates andeventual proximal bronchiectasis.
Q NO 14: A 34-year-old IV drug user who was an asymptomatic HBV carrier is hospitalized with severe hepatitis following infection with delta agent. The delta agent was able to cause hepatitis with direct HBV assistance in:A. Intracellular survivalB. Cytoplasmic penetrationC. Replication of viral RNAD. Translation of viral transcriptsE. Coating of viral particlesExplanation:Often referred to as the delta agent or the hepatitis delta virus, hepatitis D virus is a35-nm, double-shelled particle that resembles the Dane particle of HBV. The internalpolypeptide assembly of HDV is designated HDAg. Associated with this antigen is avery short circular molecule of single-stranded RNA. HDAg is considered replication-defective because it must be coated by the external coat antigen HBsAg of thehepatitis B virus. Therefore HDV infection can arise either as an acute coinfectionwith hepatitis B virus (with the HBV established first to provide the HBsAg for theHDV) or as a superinfection of a chronic HBV carrier.(Choices A, B, C, and D) Once coated with HBsAg, the hepatitis D virus is able topenetrate the hepatocyte, survive within the cell, replicate its viral RNAI andtranslate its genome into protein.Educational Objective:The HBsAg of hepatitis B virus must coat the HDAg of hepatitis D virus before it caninfect hepatocytes and multiply.
Q NO 15: A small outbreak of hepatitis A infection is reported by epidemiological services. Which of the following treatments is most likely to destroy the virus in the contaminated products?A. DryingB. Treating with 20% diethyl etherC. Treating with acid (pH = 1.0)D. Heating to 60°C for an hourF. Boiling for 1 minuteExplanation:Because hepatitis A virus (HAV) is transmitted through the fecal-oral route,improved sanitary conditions (frequent handwashing, appropriate food heating, andthe avoidance of food and water in endemic areas) serve to limit outbreaks ofinfection. When HAV contamination is a concern, the virus can be inactivated withwater chlorination, bleach (1:100 dilutions) formalin, ultraviolet irradiation, orboiling to 85°C for one minute.(Choice A) When the HAV virus is dried it is actually stable at room temperature forweeks.(Choice B) Because HAV lacks a lipid-soluble envelope, it can withstand exposure to20% diethyl ether, chloroform, or 50% trichlorofluoromethane.(Choice C) Treatment with acid does not cause sufficient damage to the hepatitis Avirus which is not surprising given that it can easily withstand the acidic gastricenvironment.(Choice D) Heating to 60°C for an hour will not inactivate HAV, though boiling to85°C for one minute is sufficient. Also recommended is autoclaving (120° for 20minutes) which is quite effective.Educational Objective:Hepatitis A virus can be inactivated water chlorination bleach (1:100 dilution)formalin, ultraviolet irradiation or boiling to 85°C for one minute.
Q NO 16: A developing country includes infant vaccination with the Haemophilus influenzae type b conjugate vaccine into its routine immunization schedule. If effectively implemented, this change in the vaccination schedule would most likely affect the epidemiology of:A. Otitis mediaB. SinusitisC. Acute bronchitisD. MeningitisE. ConjunctivitisExplanation:There are six serotypes of Haemophilus influenzae (a-f); capsular type b is the mostinvasive strain of H. influenzae and can cause sepsis, meningitis, pneumonia andother diseases. Additionally, there are unencapsulated strains referred to asnontypable Haemophilus influenzae because serotyping is based on antigens in thepolysaccharide capsule. From the time that the H. influenzae type b (Hib) protein-polysaccharide conjugate vaccine became available in 1987 for childhoodimmunization beginning at 2 months of age, there has been a dramatic decrease inthe incidence of invasive disease caused by Haemophilus influenzae type b.immunity to this and other infectious disease is accomplished during the first monthsof life by lgG antibodies acquired transplacentally from the mother, but thisprotection is only transient. H. influenzae type b conjugate vaccines prevent diseaseby the induction of active B- lymphocyte mediated humoral immunity and maydecrease oropharyngeal carriage of H. influenzae type b. Before the availability ofthe vaccine, slightly less than 50% of all cases of acute bacterial meningitis in theU.S. were caused by Haemophilus influenzae type b.(Choice A, B and E) The most common bacterial causes of acute otitis media,sinusitis AND bacterial conjunctivitis in childhood are: 1. Streptococcus peroneae, 2.Nontypable Haemophilus influenzae and 3. Moraxella catarrhalis, in that order. TheHib vaccine has no effect on nontypable strains of H. influenzae as the Hib vaccineinduces immunity specifically against the type b polysaccharide capsule, andnontypable H. influenzae do not produce capsules.(Choice C) Acute bronchitis is almost always viral in etiology with influenza A & B,coronavirus, respiratory syncytial virus and human meta pneumovirus being themost commonly implicated. Patients with viral bronchitis will often present withcough and demand antibiotics. Bacterial causes of acute bronchitis are rare andinclude Mycoplasma pneumoniae and Bordetella pertussis.Educational Objective:The Haemophilus influenzae type b vaccine is composed of cell wall polysaccharideconjugated with protein toxoid from either diphtheria or tetanus. This vaccinationcan be given as early as 2 months of age and has drastically reduced the incidenceof clinical disease caused by H. influenzae such as meningitis, pneumonia, sepsisand epiglottitis.
Q NO 17: A 14-year-old African-American female with sickle cell anemia complains of progressive exertional dyspnea after a minor febrile illness. Laboratory evaluation reveals a hematocrit of 18% and reticulocyte count of 0.5%. Which of the following viruses is most likely responsible for this patient’s current condition?A. Enveloped double-stranded DNA virusB. Non-enveloped double-stranded DNA virusC. Non-enveloped single-stranded DNA virusD. Non-enveloped (+) strand RNA virusF. Enveloped (+) strand RNA virusF. Enveloped (-) strand RNA virusExplanation:This patient has developed severe anemia after a minor febrile illness. If her bonemarrow were able to respond appropriately to the degree of anemia, the reticulocytecount would be elevated (normal reticulocyte count is 0.5-1.5% of red cells).Instead, the patient’s reticulocyte count persists at the low end of normal. Thisscenario describes an aplastic crisis, which in sickle cell patients is usually secondaryto parvovirus B19 infection of erythroid precursor cells in the bone marrow.Destruction of the erythroid precursor cells by this virus diminishes the number ofreticulocytes available to replace the deformed and/or removed erythrocytes.Parvoviruses are non-enveloped, single-stranded DNA viruses.(Choices A) Epstein-Barr virus is an enveloped, double-stranded DNA virus that cancause hematopoietic depression and some measure of aplastic anemia. However itisnot the most common cause of these findings especially in a patient with sickle cellanemia.(Choice B) Non-enveloped, double-stranded DNA viruses include adenoviruses andpapovaviruses, which are not known to commonly cause hematopoietic depressionor aplastic anemia.(Choices D and E) Hepatitis C virus (an enveloped single-stranded positive-senseRNA virus) and hepatitis E virus (a non-enveloped single-stranded positive-senseRNA virus) can cause hematopoietic depression and some measure of aplasticanemia. HIV is another enveloped single-stranded positive-sense RNA virus that cancause aplastic anemia. However these viruses are not the most common cause ofhematopoietic depression and aplastic anemia especially in a patient with sickle cellanemia.(Choice F) Important enveloped negative-sense RNA viruses includeorthomyxoviruses (eg, influenza), paramyxoviruses (eg, measles and mumps) andrhabdoviruses (eg, rabies). These viruses are not known to infect erythroidprogenitor cells in sufficient numbers to significantly impact erythropoiesis, however.Educational Objective:In patients with sickle cell anemia and other chronic hemolytic disorders the mostcommon viral cause of an aplastic crisis is infection of erythroid progenitor cells withparvovirus B19, a non-enveloped single-stranded DNA virus.
Q NO 18: Microscopic examination of lung tissue obtained from a 45-year-old Caucasian male with pulmonary infiltrates shows spherules packed with endospores. This patient’s history is likely to reveal:A. Recent travel to ArizonaB. Exposure to pigeon droppingsC. Cave exploration in OhioD. Previous cavitary tuberculosisE. Chemotherapy for leukemiaF. Long history of asthmaExplanation:Coccidioides immitis is a dimorphic fungus that has a mold form (hyphae) at 25-30°C and a yeast form (spherules with endospores) at body temperature (37-40°C).C. immitis is endemic to the southwest Unites States (southern and centralCalifornia, Arizona. New Mexico and western Texas), as well as to Northern Mexicoand some regions of Central and South America. Patients with coccidioidomycosisare likely to live in or have recently traveled to an endemic area.C. immitis is transmitted by spore inhalation. Spores are formed by fragmentation ofhyphae. Once inside the lungs, the spores turn into spherules that containendospores. The spherules subsequently rupture and release endospores thatdisseminate to other organs and tissues. Each endospore is capable of forming anew spherule.In immunocompetent hosts, C. immitis causes lung disease, which may beasymptomatic or cause flu-like symptoms (cough, fever myalgias) accompanied byerythema nodosum. Immunosuppressed patients may develop systemic cocci di o ido mycosis.(Choice B) They east form of Cryptococcus neoformans is present in pigeondroppings. This fungus causes pulmonary disease and meningoencephalitis inimmunocompromised patients.(Choice C) Histoplasma capsulatum is endemic to the Mississippi and Ohio Riverbasins found in bird and bat droppings. Patients with histoplasmosis often have ahistory of cleaning bird coops or caving.(Choice D) Aspergillus fumigatus can colonize old lung cavities (e.g. formed bytuberculosis) to form a “fungal ball” (aspergilloma). Symptoms include cough,dyspnea and hemoptysis.(Choice E) Neutropenic patients are at high risk for developing opportunisticmycoses. Candida albicans, Aspergillus fumigatus, Mucor and Rhizopus species canall cause severe disease in this population.(Choice F) Patients with asthma are at risk for developing an allergic reaction toAspergillus fumigatus, called allergic bronchopulmonary aspergillosis (ABPA). Signsand symptoms include cough, dyspnea, wheezing, fever, and migratory pulmonaryinfiltrates.Educational Objective:Coccidioides immitis is a dimorphic fungus endemic to the southwestern U.S. Itexists in the environment as a mold (with hyphae) that forms spores. These sporesare inhaled and turn into spherules in the lungs.
Q NO 19: A 45-year-old male with cough and fever is found on chest x-ray to have a lung infiltrate, hilar adenopathy, and a right-sided pleural effusion. Lung tissue obtained from this patient reveals the findings below.Which of the following is the most likely cause of this patient’s condition?A. Rhizopus speciesB. Aspergillus fumigatusC. Candida albicansD. Cryptococcus neoformansE. Blastomyces dermatitidisF. Histoplasma capsulatumG. Coccidioides immitisH. Sporothrix schenckiiExplanation:The image above shows a large spherule filled with small round endospores.Spherules are the tissue form of Coccidioides immitis. This is a dimorphic fungusthat exists in the environment in the form of mold (hyphae). It is endemic to thedesert areas of the United States and Mexico. Coccidioides can cause lung disease inimmunocompetent people and disseminated disease in the immunocompromised.Microscopic examination of body fluids, sputum, and tissue samples in 10% KOH orsilver stain shows thick-walled spherules packed with endospores. Culture onSabouraud’s agar and serology are also important in making the diagnosis.(Choice B) Aspergillus fumigatus commonly causes pulmonary disease inimmunocompromised patients. It has a mold form only. In tissue specimensAspergillus is seen as septate hyphae that branch at 45° angles.(Choice E) The characteristic appearance of Blastomyces dermatitidis is that of roundyeast with broad-based budding. These yeasts have thick, doubly refractive walls.(Choice F) Histoplasma capsulatum would be seen as small oval yeast forms withinmacrophages.Educational Objective:Coccidioides immitis infection can be asymptomatic or it can cause pulmonarydisease ranging from a flu-like illness to chronic pneumonia. It causes disseminateddisease in immunocompromised patients. Spherules containing endospores arefound in tissue samples.
Q NO 20: A 23-year-old female is brought to the ER with fever, vomiting, diarrhea and muscle pain. Her blood pressure is 90/50 mm Hg and pulse is 120/mm. Physical examination reveals erythroderma, and pelvic exam reveals a tampon in the vagina. The activation of which of the following cells is primarily responsible for this patient’s condition?A. Mast cells and eosinophilsB. Basophils and macrophagesC. Neutrophils and B lymphocytesD. Macrophages and T lymphocytesE. Platelets and mast cellsExplanation:Fever, vomiting diarrhea, muscle pain and erythroderma are the symptoms of ToxicShock Syndrome (TSS). It can rapidly progress to severe hypotension andmultisystem dysfunction. Desquamation particularly on the palms and soles canoccur 1-2 weeks after the onset of illness. TSS has been associated with the use oftampons, nasal packing etc.Staphylococcus aureus strains producing toxic shock syndrome toxin (TSST-1) areresponsible for most cases of TSS. TSST acts as a superantigen. Itis called asuperantigen because in contrast to usual antigen which activates few helper T cellsit activates large numbers of helper T cells. These toxins interact with majorhistocompatibility complex molecules on antigen presenting cells and the variableregion of the T lymphocyte receptor to cause a nonspecific widespread activation ofT lymphocytes. Activation of T cells is responsible for the release of interleukin-2 (IL-2) from the T cells and IL-1 and TNF from macrophages. These interleukins causecapillary leakage, circulatory collapse hypotension shock fever, skin findings, andmultiorgan failure.(Choice A) Eosinophil activation is associated with reactions to allergens andparasites. Peripheral eosinophilia can also be found in hypersensitivity reactions todrugs as well as with hematologic malignancies.(Choice B) Basophils are not involved in TSS.
(Choice C) B lymphocytes respond to activation by replicating and synthesizingantibodies specific for the antigen with which they were presented. B lymphocytesare not responsible for TSS.(Choice E) Mast cells when stimulated release histamine prostaglandins, leukotrienesand other inflammatory mediators. They are stimulated by the cross-linking of IgEpresent on their cell membrane by specific antigens and are active in thepathogenesis of allergic reactions and anaphylaxis.Educational Objective:Enterotoxins Exfoliative Toxins and Toxic Shock Syndrome Toxin (TSST-i) are thetoxins with superantigen activity. Superantigens interact with majorhistocompatibility complex molecules on antigen presenting cells and the variableregion of the T lymphocyte receptor to cause nonspecific “widespread” activation ofI-cells resulting in the release of interleukin-2 (IL-2) from the T cells and IL-i andTNF from macrophages. The immune cascade in turn is responsible for the effects ofTSS.
Q NO 21: A 42-year-old male presents to the emergency room following a seizure episode. Physical examination reveals oral thrush and cervical lymphadenopathy. An MRI of his brain with contrast is shown below.Which of the following is the most likely cause of his symptoms?A. NeurocysticercosisB. Mycobacterium tuberculosisC. ToxoplasmosisD. Aspergillus fumigatusE. Glioblastoma multiforme
Explanation:This contrast MIRI shows multiple ring-enhancing lesions, as indicated by thearrows. The patient also has oral thrush and lymphadenopathy. This constellation ofsigns and symptoms points to HI V-associated toxoplasmosis as the most likelydiagnosis. Seizures are a common complication of such brain lesions and theirsurrounding edema.(Choice A) Neurocysticercosis can also cause multiple brain lesions but fits less wellwith the clinical picture here than toxoplasmosis. Neurocysticercosis is uncommon inthe United States.(Choice B) Mycobacterium can also cause similar lesions but is not very common.(Choice D) Aspergillus fumigatus can cause brain abscesses in theimmunocompromised patient, but is more common in neutropenic patients andimmunosuppressed transplant recipients than individuals with HIV. Aspergillus is nota leading opportunistic pathogen in AIDS patients.(Choice E) While ring-enhancing, CNS glioblastomas are usually solitary with acharacteristic butterfly appearance.Educational Objective:The finding of multiple ring-enhancing lesions in an HIV patient is most likely due totoxoplasmosis.
Q NO 22: A 6-year-old immigrant male is brought to the emergency room with difficulty breathing and a low- grade fever. Physical examination reveals neck swelling, palatal paralysis, and a gray pharyngeal exudate. The parents are unable to provide information regarding the child’s vaccination history. Which of the following interventions is most likely to improve this patient’s prognosis?A. Antibiotic therapyB. Active immunizationC. Passive immunizationD. Adequate hydrationE. Anti-inflammatory medicationsExplanation:Diphtheria is caused by Corynebacteria diphtheriae. Acute infection of the naso- andoropharynx causes pseudomembranous pharyngitis. The diphtheria exotoxin, an ABexotoxin specific for neural and cardiac tissue causes CNS and cardiac sequelae insome patients as well. This toxin ribosylates and deactivates elongation factor- 2,thus inhibiting human protein synthesis. Clinical signs and symptoms of diphtheriainfection include sore throat, fever lymphadenopathy, upper airway dyspnea, andodynophagia. The disease is transmitted via respiratory droplets.Treatment of an acute C. diphtheriae infection requires (in order of importance): 1.administration of diphtheria antitoxin, 2. administration of penicillin or erythromycin,and 3. administration of the DPT vaccine. The diphtheria antitoxin inactivates allcirculating toxin, but is ineffective against toxin that has already gained access tocardiac or neural cells. Thus rapid administration of antitoxin is essential. Antibiotictherapy kills the bacteria, halting release of new exotoxin into the bloodstream andpreventing disease transmission. Immunization with the DPT vaccine provides lastingimmunity against future diphtheria infection.(Choice A) Antibiotic therapy is an essential component of diphtheria treatment, buthas much less effect on prognosis than antitoxin administration. This is because theexotoxin, not the bacteria, causes the major clinical sequelae. Penicillin is theantibiotic of choice in treating C. diphtheriae infection.(Choice B) Active immunization with the diphtheria toxoid (given as part of thechildhood DPT vaccine) prevents diphtheria. Diphtheria toxoid can also be given aspart of tetanus boosters in adults. In patients who are acutely ill. Vaccination doesnot help to eliminate the bacteria or the exotoxin from the body.(Choice D) While adequate hydration is an important supplementary measure inmany diseases, it does not specifically combat the disease-causing agents indiphtheria.(Choice E) Anti-inflammatory medications do not play a major role in the treatmentof diphtheria.Educational Objective:Diphtheria infection is associated with a 3% mortality rate. Cardiomyopathy is themost common cause of death. Treatment includes diphtheria antitoxin, antibioticsand immunization. Of these, the antitoxin is the most important and has thegreatest effect on prognosis.
Q NO 23: A 24-year-old female presents to clinic complaining of recurrent genital itching and vaginal discharge that responds well to topical antifungal therapy. Laboratory testing reveals that she is HIV-positive and has a CD4+ I lymphocyte countofl85/pL. The patient is at the greatest risk of developing which of the following malignant proliferations?A. H. pylon-induced B-lymphocyte proliferationB. Epstein-Barr virus-induced B-lymphocyte proliferationC. Human T lymphotrophic virus-induced B-lymphocyte proliferationD. Hepatitis B virus-induced I-lymphocyte proliferationE. BK virus-induced monocyte proliferationExplanation:Latent Epstein-Barr virus (EBV) infection is present in up to 90% of normalindividuals, with reactivation common in the immunosuppressed (eg, those withAIDS). EBV is tropic for B lymphocytes, mediating their transformation into long-term proliferating cell lines. As a result, AIDS patients have an increased incidenceof EBV-associated non- Hodgkin’s lymphomas, including the aggressive diffuse largeB-cell lymphomas and Burkitt’s lymphoma. In HIV positive patients, thedevelopment of EBV-associated non-Hodgkin’s lymphoma is preceded by a decreasein the number of functional EBV-specific CD8+ cytotoxic lymphocytes. The use ofhighly active antiretroviral therapy to replenish CD4+ T-cell counts in HI V-positivepatients can mitigate the increased risk of developing HI V-induced non- Hodgkin’slymphoma.(Choice A) Helicobacter pylon infection has been implicated in the pathogenesis ofgastric adenocarcinoma and mucosa-associated lymphoid tissue tumor (MALT0ma).It has not been established whether HIV infection influences the incidence of H.pylon-induced gastric lymphoma.(Choice C)The retrovirus HTLV-I is associated predominantly with adult T-cellleukemia and lymphoma, not B- lymphocyte proliferations.(Choice D) Hepatitis B virus (HBV) infection is associated with hepatocellularcarcinoma not T-lymphocyte proliferation.(Choice E) The BK virus is a DNA virus in the Papovaviridae family that primarilycauses one of two diseases in the immunocompromised: nephropathy (typicallypost-transplant, when the latent infection is reactivated) or hemorrhagic cystitis. Acausal relationship between BK virus infection and malignant monocyte proliferationin HI V-positive patients has not been established.Educational Objective:HI V-positive patients often experience reactivation of latent EBV infections with aresulting increased incidence of EBV-induced lymphoproliferative disorders, includingthe aggressive non-Hodgkin’s diffuse B-cell lymphomas.
Q NO 24: A 34-year-old female presents to your office with perineal pruritus and vaginal discharge. Her past medical history is significant for acute sinusitis one week ago as well as allergic rhinitis. Pelvic examination shows erythematous vulva and thick adherent, “cottage cheese-like” vaginal discharge. Microscopic examination of the vaginal discharge reveals budding cells. This patient’s condition was most likely preceded by:A. Decreased thickness of the vaginal epitheliumB. Increased glycogen concentration in the vaginal epitheliumC. Decreased number of Gram-negative bacteria in the vaginaD. Increased alkaline secretions by the cervical mucosaE. Depressed T-lymphocyte response to mucosal stimuliExplanation:Gram-negative lactobacilli comprise a major part of the normal vaginal flora. Otherimportant colonizers include Corynebacteria, fungi (Candida) Streptococcus group B,and E. coil. These species exist in balance at the normal vaginal pH of 3.8 - 4.2.Changes in vaginal pH, damage to the vaginal microflora, and epithelial injury can alllead to increased growth of Candida and symptoms of vulvovaginitis. Candidavaginitis is the second most common cause of vaginitis.Common triggers for Candida vaginitis include:1. Antibiotic use suppresses normal bacterial flora, facilitating Candida overgrowth.This patient’s history of acute sinusitis suggests recent antibiotic treatment.2. Contraceptives both oral and typical alter vaginal pH.3. Corticosteroid therapy.4. Uncontrolled diabetes mellitus.5. Any other cause of immunosuppression, including HIV.Patients with Candida vaginitis complain of vulvar pruritus and white, thickdischarge. Physical examination reveals erythema of the vulvar and vaginal mucosaand “cottage-cheese”-like discharge. Vaginal pH is normal or slightly higher thannormal (>4.5). Wet mount examination is diagnostic: it reveals budding yeast andpseudohyphae.(Choices A and B) Decreased thickness of the vaginal epithelium and decreasedamounts of glycogen in epithelial cells are characteristic of postmenopausal andlactating women. These changes are caused by low estrogen levels and lead toatrophic vaginitis. Yeast would not necessarily be isolated from the vaginal dischargeof these patients.Educational Objective:Use of broad-spectrum antibiotics suppresses the normal bacterial flora of the vaginaand facilitates Candida overgrowth. Antibiotic use is the most common cause ofCandida vaginitis. Other potential causes include contraceptives, steroids, diabetesmellitus and immunosuppression.
Q NO 25: Viral particles have been isolated from the peripheral blood of an 8- year-old male. The particles are non-enveloped and contain single-stranded DNA. The patient most likely suffers from:A. Acute hepatitisB. BronchiolitisC. RubellaD. Erythema infectiosumE. ChickenpoxF. MumpsExplanation:There is only one clinically significant viral family in which the members are bothnon-enveloped and contain single- stranded DNA: Parvoviridae, which includes thesmallest DNA nucleocapsid viruses. Particularly renowned as a human pathogen isparvovirus B19, which is associated with erythema infectiosum (“fifth disease”)aplastic crises in those with sickle cell anemia, and hydrops fetalis (particularly wheninfection occurs before the 20th week of gestation).(Choice A) The major pathogens responsible for acute viral hepatitis are shown inthe table below.The only virus with a DNA genome is hepatitis B, but this virus is enveloped andcontains double-stranded DNA.(Choice B) The major viruses responsible for bronchitis/bronchi colitis are influenzaA, respiratory syncytial virus (RSV)I and coronavirus. These are all enveloped RNAviruses.(Choice C) Rubella (German measles) arises secondary to infection with a togavirus.The Togaviridae family consists of enveloped RNA-containing viruses.(Choice E) Chickenpox is due to varicella zoster virus (VZV). This is a member of theherpesvirus family, which consists of enveloped virions that all contain double-stranded DNA genomes.(Choice F) Mumps is caused by a member of the paramyxovirus family, whichconsists of enveloped virions that contain an RNA genome.Educational Objective:There is only one clinically significant viral family in which the members are bothnon-enveloped and contain single stranded DNA: Parvoviridae. Parvovirus B19causes erythema infectiosum (fifth disease), aplastic crises in sickle cell anemia, andhydrops fetalis.
Q NO 26: Blood cultures from a 54-year-old male recently diagnosed with Hodgkin’s disease reveal motile Gram positive rods that produce a very narrow zone of j3-hemolysis on sheep blood agar. Which of the following processes is most important in eliminating these bacteria from the body?A. Terminal complement cascadeB. Eosinophil actionC. Immunoglobulin secretionD. Neutrophil oxidative burstE. Cell-mediated immunityExplanation:Listeria monocytogenesis, a Gram positive rod that produces a very narrow zone ofbeta-hemolysis on sheep blood agar, similar to the pattern produced by colonies ofβ-hemolytic Streptococci. L. monocytogenes shows tumbling motility at 22°C but canbe cultured at temperatures as low as 4°C. It is a facultative intracellular parasiteand the only Gram positive bacteria to produce lipopolysaccharide (LPS) endotoxin.Listeria can cause serious disease (meningitis septicemia) in newborns, pregnantwomen, the elderly and immunocompromised patients, but rarely causes disease inimmunocompetent individuals.Macrophages ingest L. monocytogenes, which survives phagocytosis and can go onto multiply in the cytoplasm. In healthy individuals, the cell-mediated immuneresponse stimulates the production of cytokines (interferon gamma, tumor necrosisfactor-beta and interleukin-12) that induce a cytotoxic T-cell response andmacrophage activation and killing of intracellular Listeria. In patients withcompromised cell-mediated immunity, however, the organism survives and diseaseresults (Choice E).There are two types of listeriosis, neonatal and adult. In neonatal listeriosis, theorganism is transmitted from the mother to the fetus transplacentally or during fetalpassage through the vaginal canal. In both adults and neonates listeriosis can betransmitted by the consumption of contaminated food.(Choice A) Patients with inherited deficiencies of the terminal complement cascade(C5b-C9) are unable to form the membrane attack complex (MAC) and will have apredisposition to recurrent Neisseria infections. (Choice B) Eosinophil action isimportant for eradicating parasitic infections from the body. (Choice C) X-linkedagammaglobulinemia of Bruton is a condition causing a pure defect ofimmunoglobulin synthesis and secretion. Patients lack humoral immunity but haveintact cell mediated immunity. These patients are therefore at increased risk forbacterial infections by Streptococci and Staphylococci but have normal responses toinfections by Listeria, viruses and fungi. (Choice D) Defects in the neutrophiloxidative burst lead to chronic granulomatous disease (CGD). This is an X linkeddisorder that causes decreased NADPH oxidase activity and a failure of themyeloperoxidase system resulting in an inability to form hydrogen peroxide andoxygen free-radicals in concentrations high enough to kill catalase producingorganisms like S. aureus.Educational Objective: 1. Intact cell-mediated immunity is essential for theelimination of Lister/a monocytogenes from the body. Neonates up to 3 months ofage are especially vulnerable because they have yet to fully develop their cellmediated immunity. Listeria rarely causes disease in normal healthy adults.2. This bacterium produces a very narrow zone of beta-hemolysis on sheep bloodagar (resembling the pattern produced by β-hemolytic Streptococci), shows tumblingmotility at 22°C, and can be cultured at temperatures as low as 4°C.
Q NO 27: A 54-year-old male is brought to the ER with a one-week history of headaches and progressive confusion. He was hospitalized six months ago with viral esophagitis and two months ago with pneumocystic pneumonia. Lumbar puncture is performed, and shows a moderate increase in CSE protein concentration and CSE pleocytosis. The latex agglutination test is positive for soluble polysaccharide antigen. Light microscopy of this patient’s CSF is most likely to reveal:A. Nonseptate hyphaeB. Germ tubesC. Budding yeastD. SpherulesE. SporangiumExplanation:A recent history of viral esophagitis and pneumocystis pneumonia is virtuallydiagnostic of HIV infection. The patient’s headache, confusion, and inflammatory CSFchanges are typical symptoms of meningitis. CNS infection in an HIV (+) patient islikely to be caused by Cryptococcus neoformans, an opportunistic fungus that causesmeningitis (or meningoencephalitis) in immunosuppressed patients.For study purposes, the medically important facts regarding C. neoformans aresummarized below:(Choice A) Nonseptate hyphae that branch at wide angles are characteristic of Mucorand Rhizopus species. These fungi cause infection of the paranasal sinuses(mucormycosis) in immunosuppressed patients.(Choice B) Candida albicans forms germ tubes (sprouts of true hyphae from yeastcells) if incubated in 37°C serum for3 hours. This test helps to differentiate C.albicans from other Candida species. Candida albicans does not usually causemeningitis.(Choice D) Spherules (round structures containing endospores) are found in thetissue form of Coccidioides immitis. This fungus causes lung disease anddisseminated mycosis, but is not commonly associated with meningitis (rarely it cancause meningitis).(Choice E) Sporangium is a structure that produces and contains spores. It is
present in mold fungi. Cryptococcus has only a yeast form and thus does not havesporangia.Educational Objective:Cryptococcus neoformans causes meningoencephalitis in HIV (+) patients. The latexagglutination test detects the polysaccharide capsule antigen of Cryptococcus and isused for diagnosis. India ink staining of the CSF shows round or oval budding yeast.
Q NO 28: A 38-year-old male intravenous drug user hospitalized for high-grade fever, fatigue and dyspnea dies in the intensive care unit (ICU). His lung autopsy findings are shown on the slide below.This patient most likely suffered from:A. Mycotic aortic aneurysmB. Tricuspid valve endocarditisC. Severe small airway obstructionD. Miliary tuberculosisE. Venous thromboembolismExplanation:The above slide illustrates wedge-shaped hemorrhagic pulmonary infarcts.Pulmonary infarcts are almost always hemorrhagic due to the dual blood supply tothe lungs (pulmonary and bronchial arteries). The question stem describes a youngmale patient with a history of intravenous drug abuse dying of sepsis. Intravenousdrug abusers most commonly form endocarditis of the right heart. Recall that S.aureus is the most common endocarditis associated with IVDU. Pulmonary infarctionin this case likely resulted from septic embolization from the tricuspid valve to adistal pulmonary artery.(Choice A) Mycotic aneurysm could also result from endocarditis. However the aboveshowed multiple infarcts in a patient with high grade fevers favor right sided valveendocarditis as the primary cause. Despite their name, mycotic aneurysms are onlyvery rarely associated with fungal infections.(Choice C) Severe small airway obstruction is not associated with infection andwould not cause the clinical picture described. It would additionally not causepulmonary infarction. Small airway obstruction is characteristic of asthma.(Choice D) Pulmonary tuberculosis classically affects the apical sections of the lungsas well as the hilar lymph nodes after initially establishing infection by inhalation andestablishment of a Ghon complex in the middle or lower lobes. Progression ofdisease leads to the formation of caseating granulomas and the formation of cavitarypulmonary lesions.(Choice E) Venous thromboembolism would not cause high-grade fevers.Educational Objective:S. aureus is the most common cause of tricuspid endocarditis in intravenous drugusers. P. aeruginosa is the second most common cause in this patient population.These patients can develop multiple septic emboli in lungs. Pulmonary infarcts arealmost always hemorrhagic due to the dual blood supply to the lungs (pulmonaryand bronchial arteries).
Q NO 29: In a research experiment, Strain of Streptococcus pneumoniae produces no effects when injected into the mouse peritoneal cavity. However, when grown on media alongside a virulent strain of S. pneumoniae (Strain 2), Strain acquires the ability to cause death. Which of the following processes most likely accounts for this acquisition of virulence?A. Pilus-mediated transferB. Chromosomal fragment uptake from mediaC. Phage-mediated DNA transferD. Spontaneous mutationE. Transposon-mediated DNA transferExplanation:Certain strains of S. pneumoniae express capsular polysaccharides that inhibitphagocytosis, making it a successful pathogen. Strains lacking the capsule are notpathogenic. S. pneumoniae is able to undergo transformation, a process involvinguptake and expression of chromosomal fragments from the environment, whenneighboring bacteria die and lyse (Choice B). Bacteria capable of taking up free DNA,that is, capable of undergoing transformation, are said to be ‘competent.’Streptococcus pneumoniae, Haemophilus influenza and Neisseria meningitidis arebacteria that have this ability. Through this process, non-virulent, non-capsule-forming strains of S. pneumoniae can acquire the genetic material that codes for thecapsule and thus gain virulence.(Choice A) Conjugation is pilus-mediated DNA transfer. Conjugation was firstdescribed in E. coil, but we now know that most bacteria are capable of the process.To initiate conjugation, the donating bacterium must produce a sex pilus, whichcreates a direct connection with the receiving bacterium. Only bacteria with geneticmaterial coding for conjugative ability (e.g. the F plasmid) can initiate conjugation inthis way. Next, the donating bacterium synthesizes a new DNA strand, which ispassed through the pilus into the recipient organism. In the receiving organism, thecomplementary DNA strand is synthesized.(Choice C) In transduction, a bacteriophage (virus) transfers DNA from one bacterialcell to another. While replicating within the infected host bacterium, thebacteriophage may incorporate host bacterial DNA into the phage particle. When thephage is subsequently released, it transfers both phage DNA and DNA from thepreviously infected bacterium into the newly infected cell. By this mechanism,bacteria can acquire genes for virulence and antibiotic resistance.(Choice D) A mutation is a change in the nucleotide sequence of a gene. Mutationalchanges may be spontaneous or induced. Changes in the nucleotide base sequencecan cause changes in the transcribed mRNA base sequence, potentially altering theamino acid sequence of the protein product. Through this mechanism, a bacteriummay begin to form proteins with potentially useful functions to aid in bacterialsurvival.(Choice E) Transposon-mediated DNA transfer is a mechanism by which DNA fromplasmids or phage transfer can be incorporated into the host bacterium’s DNAgenome, genetic material can be moved from one position to another within thegenome, or DNA can be removed from the genome and placed onto a plasmid. Thelocation of a gene in the genome is important because it determines its proximity topromoter or suppressor regions.
Educational Objective:S. pneumoniae is able to undergo transformation, which is the uptake andexpression of chromosomal fragments from the environment made available whenanother bacterial cell dies and undergoes lysis.Conjugation is pilus-mediated transfer of DNA. Conjugation occurs in most bacteriabut was first described in the gram negative rod E. coil.In transduction, DNA from one bacterial cell is transferred to another bacterial cellby a bacteriophage (virus).
Q NO 30: Monoclonal antibodies against complement receptor CD21 on the surface of B-lymphocytes could prevent infection with which of the following viruses?A. Parvovirus B19B. Human immunodeficiency virusC. Epstein-Barr virusD. CytomegalovirusE. AdenovirusExplanation:Essential to viral invasion of cells and the viral tropism for specific tissues is theinitial attachment of the virion envelope or capsid surface proteins to thecomplementary host cell surface receptors. Many viruses bind to normal host cellplasma membrane receptors in order to enter host cells.Epstein-Barr virus (EBV) is the ubiquitous herpesvirus responsible for acuteinfectious mononucleosis, nasopharyngeal carcinoma lymphomas, and Burkitt’slymphoma. More than 90% of the normal adult population is seropositive for EBV,which is primarily transmitted through contact with oropharyngeal secretions. TheEBV envelope glycoprotein gp350 binds to the cellular receptor for the C3d portion ofcomponent (CR2 or CD21). CD21 is normally present on the surface of B cells andnasopharyngeal epithelial cells. Thus, a monoclonal anti-CD21 antibody couldinterfere with the attachment of EBV to cells.(Choice A) Parvovirus B19 is thought to attach to human erythroid cells via the bloodgroup P antigen (globoside). The P antigen is expressed by mature erythrocytes,erythroid progenitors, megakaryocytes, placenta, and the fetal liver and heart.Immature cells of the erythroid family are most vulnerable to parvovirus B19infection, which is why adult bone marrow and fetal liver are principal targets. Viralreplication causes cell death.(Choice B) HIV viruses attach to their major target host cells (CD4+ T cells)primarily via the binding of viral envelope glycoprotein gpl2O to the cellular CD4transmembrane glycoprotein and the coreceptor (CCR5 orCXCR4). The HIV envelopethen undergoes a conformational change that activates gp4l and initiates membranefusion.(Choice D) Like the other herpesviruses, cytomegalovirus (CMV) requires initialcontact with glycosaminoglycan chains on host cell surface proteoglycans for entryinto the host cell.(Choice E) The adenovirus has hexon and penton capsomeres on its surface. Rodlikestructures (“fibers”) that project from the penton base capsomeres are responsiblefor mediating adsorption to host cells. The cell receptor for most adenovirus fibers isa transmembrane protein member of the immunoglobulin superfamily.Educational Objective:Essential to viral invasion of cells and the viral tropism for specific tissues is theinitial attachment of the virion envelope or capsid surface proteins to thecomplementary host cell surface receptors. Many viruses bind to normal host cellplasma membrane receptors in order to enter host cells. Known host cell receptor—virion/virion protein binding specificities include: CD4 and HIV gp120; CD21 and EBVgp350; and erythrocyte P antigen and parvovirus B19.
Q NO 31: A 54-year-old male presents to the ER with a sore on his right shoulder. Physical examination demonstrates an ulcer with central black eschar surrounded by edema. Exudate microscopy reveals chains of large Gram-positive rods. Which of the following would be most helpful in making the diagnosis?A. Family historyB. OccupationC. Recent contact with foreignersD. AllergiesE. Current medicationsF. Sexual historyG. Prior ER visitsExplanation:Humans become infected with Bacillus anthracis most commonly by exposurethrough contact with infected animals or animal products or through use of B.anthracis as a biological weapon. For this reason an occupational history of exposureto animals or animal products is extremely important; if cutaneous anthrax issuspected in a patient without the risk of occupational exposure, then the potentialfor bioterrorism should be suspected and public health authorities contacted. Thedisease is rare in the Unites States; it is most common in areas where vaccination oflivestock and animal carriers is not done or not possible.Growth of the vegetative organisms at the site of inoculation results in formation ofa characteristic edematous wound with central necrosis leading to formation of ablack eschar. B. anthracis spreads via lymphatics to the bloodstream, and theorganism multiplies in the blood and tissue. Cutaneous anthrax is the most commonform of this disease; pulmonary anthrax accounts for approximately 5% of cases,and gastrointestinal anthrax is a rare occurrence. Cutaneous anthrax commonlyoccurs on exposed surfaces of the arms or hands, and sometimes on the face andneck.(Choice A) Family history would not be helpful in making the diagnosis of anthrax asthere is no genetic predisposition to this disease.(Choice C) Recent contact with foreigners would not be a consideration in diagnosinganthrax as this organism is not transmitted from person to person.(Choice D) Allergies are not a reasonable choice, because formation of a necroticskin wound is not a common allergic response.(Choice E) Current medications would be a consideration as drugs can induce avariety of cutaneous findings, but they generally do not cause discrete areas ofeschar as mentioned in this question stem.(Choice F) Sexual history is not a consideration because anthrax is not a sexuallytransmitted disease.(Choice G) Prior ER visits are not a factor in diagnosing anthrax because anthrax isnot a nosocomial infection and a visit to the ER would not be an exposure risk.Educational Objective:Cutaneous anthrax leads to the formation of a necrotic skin wound with anerythematous and edematous border and a necrotic center after inoculation ofspores of Bacillus anthracis into the skin. Anthrax is most commonly acquiredoccupationally by those who handle livestock that have not been immunized for thedisease as well as those who handle the hides of such animals. Anthrax is also usedas a biological weapon due to the near 100% mortality of the pulmonary form.
Q NO 32: A 25-year-old male with a several month history of fluctuating levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) is found to have high titers of lgG directed against hepatitis C envelope protein. These antibodies do not confer effective immunity against the infection because:A. The antibodies do not have neutralizing propertiesB. Envelope proteins vary their antigenic structureC. Envelope proteins have low immunogenicityD. Envelope proteins are lost after recurrent replicationsE. Envelope proteins are sequestered within the hepatocytesExplanation:Hepatitis C virus has six or more genotypes and multiple sub genotypes, asdemonstrated by the genetic differences in the encoding of its two envelopeglycoproteins. This genetic variation has led to the development of a hypervariableregion of the envelope glycoprotein that is especially prone to frequent mutation.Moreover, there is no proofreading 3’ — 5’ exonuclease activity built into the virion-encoded RNA polymerase. As a result, the RNA polymerase makes many errorsduring replication, with several dozen subspecies of hepatitis C virus typicallypresent in the blood of an infected individual at any one time. Because of thisremarkable variety in the antigenic structure of the HCV envelope proteins,production of host antibodies lags behind the production of new mutant strains ofHCV and effective immunity against infection is not conferred. The tremendousantigenic variety of HCV has significantly slowed efforts to develop a vaccine againstthe virus.(Choice A) Host antibodies against hepatitis C virus do have neutralizing propertiesand are effective in eliminating the more established hepatitis C strains. It is theconstantly emerging mutant strains that pose the greatest challenge to the hostimmune system.(Choice C) The envelope proteins of hepatitis C virus are highly immunogenic.(Choice D) The envelope proteins of hepatitis C virus are not lost after recurrentreplications.(Choice E) The envelope proteins of hepatitis C virus are not sequestered withinhepatocytes. Rather, these envelope proteins are present on the outermost surfaceof the virus and facilitate entrance into hepatocytes.Educational Objective:Because of the remarkable variety in the antigenic structure of hepatitis C virusenvelope proteins, the production of host antibodies lags behind the production ofnew mutant strains of HCV and effective immunity against infection is not conferred.
Q NO 33: A 34-year-old immigrant from Eastern Europe presents to your office with a three-month history of productive cough, night sweats and low-grade fever. Sputum cultures grow budding yeast that form germ tubes at 37°C. The most likely site of this organism before entering the sputum is which of the following:A. Fibrous lung cavitiesB. Inflamed lung parenchymaC. Bronchioles and small bronchiD. Large bronchi and tracheaE. Oral cavityExplanation:Candida albicans gives rise to true hyphae, termed “germ tubes.” when incubated at37°C for 3 hours. Germ tubes are specific for C. albicans; they are not seen with anyother Candida species. Morphologically, all Candida fungi are yeasts, seen in tissuesections as single cells with pseudohyphae.Candida albicans is the most common opportunistic mycosis. It is also a frequentcolonizer of human skin and mucous membranes. (Candida contributes to thenormal flora of skin, mouth, vagina, and intestine.)Superficial Candida infections are associated with antibiotic use, corticosteroid use,diabetes mellitus, HIV and other immunosuppressing illnesses. These superficialinfections include oral thrush vulvovaginitis and cutaneous candidiasis. Disseminatedcandidiasis occurs in neutropenic patients and most often affects the esophagus,heart, liver and kidney.Candida does not usually cause lung disease. This patient’s pulmonary symptoms(cough, night sweats and low- grade fever) as well as the fact that he has comefrom Eastern Europe, are consistent with a diagnosis of tuberculosis. The Candida inhis sputum indicates only that his oral cavity is colonized: it does not contribute tothe diagnosis.(Choice A) Aspergillus fumigatus is a fungus that colonizes already-existing lungcavities. It forms a “fungus ball” (aspergilloma) that may cause cough andhemoptysis.(Choice B) Many pathogens, including bacteria viruses and fungi, can causeinflammation of the lung parenchyma. Candida-associated pulmonary disease isuncommon, however.(Choices C and D) The trachea and large and small bronchi are normally sterile.Educational Objective:Candida albicans is a normal inhabitant of the 01 tract (including the oral cavity) inup to 40% of the population. Thus it is a common contaminant of sputum cultures.The presence of Candida in sputum does not indicate disease.
Q NO 34: Infective endocarditis is known to be caused by many different bacterial species. Which of the following scenarios is most consistent with infective endocarditis caused by Streptococcus bovis?A. A 34-year-old female with known mitral stenosis develops low-grade fevers andnegative blood culturesB. A 45-year-old male complains of fatigue and exertional dyspnea three weeks aftertooth extractionC. A 62-year-old female has a persistent fever after being diagnosed with coloncancerD. A 64-year-old male with repeatedly negative blood cultures has small mitralvegetation on transesophageal echocardiogramE. A 29-year-old male with a persistent fever has tricuspid vegetations and tricuspidregurgitation on transthoracic echocardiogramExplanation:Among non enterococcal group D streptococci, Streptococcus bovis is the one mainhuman pathogen. Streptococcus bovis is a part of the normal flora of the colon, andbacteremia or endocarditis caused by S. bovis is associated with colonic cancer inapproximately 25% of cases. S. bovis causes a subacute bacterial endocarditis withsymptoms similar those of S. viridans SBE. In addition to its association with colonicmalignancy, S. bovis endocarditis is unique in that the majority of cases that occurdo so in patients with no preexisting valvular abnormality. The role of S. bovis ascausative agent or marker of the disease in colon cancers is unclear, but everypatient with S bovis bacteremia with or without endocarditis should be examined fora G1 tract malignancy.(Choice A) This clinical picture is most consistent with a patient who has sufferedfrom acute rheumatic fever in the past which has left her with mitral stenosis. It islikely that she has recently experienced yet another episode of rheumatic fever.(Choice B) This scenario is most consistent with Streptococcus viridans subacutebacterial endocarditis. S. viridans is the most common etiologic agent in subacutebacterial endocarditis (SBE) following dental work.(Choice D) This case is most consistent with culture-negative endocarditis. Theseorganisms include, but are not limited to Bartonella, Coxiella, Mycoplasma,Histoplasma, Chlamydia and the HACEK organisms (Haemophilus, Actinobacillus,Cardiobacterium, Eikenella and Kingella).(Choice E) Right-sided endocarditis commonly occurs in IV drug users and istypically caused by S. aureus.Educational objective:S. bovis endocarditis and S. bovis bacteremia are associated with GI lesions (coloncancer) in more than 25% of cases. When S. bovis is cultured in the blood workupfor colonic malignancy with colonoscopy is essential.
Q NO 35: A 3-year-old male experiences several episodes of otitis media. Middle ear exudate cultures grow H. influenzae although the patient’s immunizations are up-to-date. Which of the following explains H. influenzae infection in this patient despite immunizations?A. No vaccine is effective against H. influenzaeB. The strains responsible for this patient’s disease produce exotoxinC. The strains responsible for this patient’s disease do not produce capsuleD. H. influenzae infection despite immunizations means defective cellular immunityE. H. influenzae infection despite immunizations signifies defective neutrophilfunctionExplanation:H. influenzae along with Streptococcus pneumoniae are the most frequent causes ofacute otitis media. This infection is primarily seen in children between 6 months and12 years of age. More than 90% of H. influenzae strains isolated from middle earaspirates of infected children are nontypable; the remaining 10% are H. influenzaetype b. H. influenzae is classified or typed, based on the antigens in itspolysaccharide capsule, and strains of H. influenzae that do not produce a capsuleare referred to as nontypable. Nontypable H. influenzae strains are part of the upperrespiratory tract normal flora, but they can also cause otitis media, sinusitis andbronchitis in adolescents and adults as well as children and vaccination with the H.influenzae type b (Hib) vaccine does not confer immunity to any strain except typeb.It is recommended that all children receive the Hib vaccine beginning at 2 months ofage as H. influenzae type b is associated with disseminated disease, pneumoniaepiglottitis and meningitis.(Choice A) The protein-conjugated Hib vaccine is very effective in inducing immunityto H. influenzae type bin children as young as two months old.(Choice B) Exotoxin is not produced by any strain of H. influenzae, typable or not.The vaccine for H. influenzae is directed against capsular polysaccharide, not toxinor toxoid.(Choice D) H. influenzae infection specifically with H. influenzae type b despiteimmunization with the Hib vaccine does not indicate defective cellular immunity as aT-cell response is generally not induced even by the conjugate vaccine. Theconjugate vaccine effectively stimulates B-cells leading to the generation of memoryB-lymphocytes and humoral immunity to Hib.(Choice E) H. influenzae infection despite immunizations does not necessarily signifydefective neutrophil function although poor neutrophil function or low neutrophilcount can predispose to bacterial disease. Neutrophil function is impaired in chronicgranulomatous disease Chédiak-Higashi syndrome and other inherited diseases.Educational Objective:Nontypable strains of Haemophilus influenzae are strains of H. influenzae that do notform an antiphagocytic capsule. They are part of the normal flora of the upperrespiratory tract, but can cause otitis media sinusitis and bronchitis. Immunity tonontypable strains as well as capsular strains other than type b is not conferred byvaccination with the Hib vaccine.
Q NO 36: An 18-month-old male is seen on an outpatient basis for fever, runny nose, and sore throat. Two days later, he is brought to the emergency department with persistent fever, brassy cough and di1ticultc breathing. Physical examination reveals stridor. Which of the following pathogens is most likely responsible for this patient’s condition?A. RhinovirusB. ParamyxovirusC. TogavirusD. ParvovirusE. CalicivirusExplanation:This child initially presented with fever, rhinitis, and pharyngitis, symptoms of anupper respiratory tract infection (URI). Most URIs (with or without pharyngitis) arecaused by viruses, with roughly 15-20% of childhood cases of pharyngitis and 5-10% of adulthood cases of pharyngitis caused by bacteria. The various viral causesof URIs are listed below:When a URI-stricken child such as this one develops a brassy cough and breathingdifficulties, it is likely he has developed acute laryngotracheobronchitis (croup). Thedyspnea associated with croup occurs when inflamed subglottic tissue obstructs theupper airway, and the characteristic stridor of croup is a sign that the URI hasspread to include the larynx. Croup is typically caused by the standard URI viruseswith the parainfluenza viruses (members of Paramyxoviridae) most commonlyresponsible.(Choice A) Rhinovirus is the most common viral cause of upper respiratory infectionsbut is an uncommon cause of viral croup.(Choice C) Togaviruses are responsible for rubella (German measles) and Easternand Western equine encephalitis. (Choice D) Parvoviruses are responsible foraplastic crises in sickle cell anemia, erythema infectiosum (fifth disease), andhydrops fetalis.(Choice E) Caliciviruses (hepatitis E virus and Norwalk virus) are responsible for viralgastroenteritis.Educational Objective:Brassy cough with dyspnea in a child with a recent URI history is suggestive of virallaryngotracheobronchitis (croup). The most common cause of croup is parainfluenzavirus type 1.
Q NO 37: A 32-year-old male presents to his physician complaining of diarrhea, flatulence, foul-smelling stools, and abdominal cramping. He recently returned home from a hiking trip. A smear of his stool sample is shown below: Which of the following is the drug of choice for this condition?A. CiprofloxacinB. MetronidazoleC. MebendazoleD. AlbendazoleE. LoperamideF. ClindamycinG. ErythromycinExplanation:When examined for ova and parasites (stool smear with iodine staining) thispatient’s stool reveals ellipsoidal cysts with smooth well-defined walls and 2+ nucleiconsistent with Giardia lamblia. Giardia is the most common enteric parasite in theU.S. and Canada. When an individual drinks contaminated water from an endemicarea without first boiling it, Giardia can colonize the duodenal and jejunal mucosallining. Giardiasis causes chronic diarrhea malabsorption and flatulence.Metronidazole is an accepted treatment for this protozoan flagellate. This drug canalso be used to treat Helicobacter pylori infections amebiasis and trichomoniasis.(Choice A) Inflammatory traveler’s diarrhea (marked by stool containing blood andmucus) can be treated with ciprofloxacin or another fluoroquinolone.(Choice C) Mebendazole is an anti-helminthic drug that acts on the microtubules ofroundworms like Ancylostoma, Ascaris and Enterobius.(Choice D) Albendazole is used to treat the tapeworm (cestode) Echinococcusgranulosus. Echinococcus does not commonly cause diarrhea, but rather producescysts in the liver and elsewhere.(Choice E) Loperamide is an opiate antimotility drug that may be prescribed in somecases of traveler’s diarrhea where there is no fever or blood in the stool.(Choice G) Erythromycin can be used in lieu of fluoroquinolones to treatCampylobacter jejuni, as this organism has shown increasing worldwide resistanceto fluoroquinolones.Educational Objective:This iodine-stained stool smear shows Giardia lamblia cysts. Giardia is the mostcommon enteric parasite in the U. S. and Canada and is a common cause of diarrheain campers/hikers. Metronidazole is the treatment of choice.
Q NO 38: Cytomegalovirus (CMV) is isolated from the urine sample of a 26-year- old male. Which of the following manifestations of CMV disease is most commonly seen in immunocompetent adults?A. Vesicular skin rashB. MononucleosisC. Viral pneumoniaD. RetinitisE. HepatitisF. Esophageal ulcerExplanation:Cytomegalovirus (CMV) is a rare cause of disease in the immunocompetent, with thevirus more typically responsible for subclinical infection. When primary CMV infectiondoes result in clinically evident illness afflicted individuals appear to have a systemicmononucleosis-like syndrome characterized by fever, malaise, myalgia, atypicallymphocytosis, and elevated liver transaminases. In contrast to EBV mononucleosis,heterophil antibodies are not usually present in patients with CMV mononucleosis.(Choice A) A vesicular skin rash is frequently seen in association with herpes simplexand herpes zoster.(Choice C) CMV pneumonitis is common after organ transplantation.(Choice D) Retinitis is the most common manifestation of CMV infection in patientswho are HI V-positive.(Choice E) Disseminated CMV can cause diarrhea and hepatitis in theimmunocompromised.(Choice F) Odynophagia (painful swallowing) associated with linear esophagealulcers is often reported by HIV positive patients.Educational Objective:CMV is typically associated with subclinical infection in the immunocompetent, withthe occasional individual developing a mononucleosis-like syndrome that is Monospotnegative. In the immunocompromised, prima or reactivated CMV infection can resultin severe retinitis, pneumonia, esophagitis, colitis, and/or hepatitis.
Q NO 39: An 8-year-old male is brought to the ER with a two day history of fever, abdominal pain and diarrhea. Careful history taking reveals that the patient’s pet puppy had diarrhea one week ago. Aside from the present episode, the patient has no significant past medical history and all of his vaccinations are up-to-date. His stool is negative for ova and parasites. Which of the following is the most likely cause of this patient’s symptoms?A. Staphylococcus aureusB. ShigellaC. CampylobacterD. Bacillus cereusE. Vibrio parahemolyticusF. Giardia lambliaExplanation:Of the enteric pathogens listed in the answer choices, only Campylobacter speciescan be transmitted from domestic animals to humans. Campylobacter is a curvedGram negative rod with a filament that allows it to move in a characteristic“corkscrew” fashion. Campylobacter jejuni is the most common cause of acutegastroenteritis in children and adults in industrialized countries. Transmission is viathe fecal-oral route. The organism can be acquired from:1. Domestic animals, such as cattle, sheep, dogs, and chickens. This route oftransmission is common in farm and laboratory workers.2. Contaminated food, such as undercooked poultry and unpasteurized milk.Campylobacter species cause inflammatory diarrhea (initially watery, later bloody),accompanied by abdominal cramping, tenesmus and leukocytes in stool. Theabdominal pain may mimic appendicitis. Campylobacter is the most commoninfectious agent associated with Guillain-Barré syndrome.(Choice A) Gastroenteritis caused by S. aureus results from the action of apreformed exotoxin and is associated with consumption of certain precooked foodsdairy products, custard and mayonnaise. This disease is more commonly associatedwith vomiting and abdominal cramps than diarrhea.(Choice B) Shigella is a human pathogen transmitted via the fecal-oral route by dirtyhands, fomites in daycare centers, and food contaminated by unhygienic handlers.Domestic animals do not carry this pathogen.(Choice D) Bacillus cereus survives on steamed and fried rice where it produces aheat-stable enterotoxin. (Choice E) Vibrio parahemolyticus is transmitted byconsumption of contaminated shellfish.(Choice F) Giardia lamblia infection is commonly acquired by drinking contaminatedwater. A history of camping, hiking in the mountains and white-water rafting areclassically associated with giardiasis.Educational Objective:Campylobacter infection is a common cause of inflammatory gastroenteritis and canbe acquired from domestic animals (cattle, chickens, dogs) or from contaminatedfood. The diarrhea is inflammatory and is accompanied by fever, abdominal pain andtenesmus. Campylobacter infection is associated with Guillain-Barré syndrome.
Q NO 40: A 78-year-old nursing home resident develops high fevers, chest pain and cough productive of rusty sputum. Sputum microscopy reveals numerous lancet-shaped Gram positive cocci in pairs. The patient dies despite aggressive hydration and antibiotic treatment. A vaccine containing which of the following might have prevented this outcome?A. Recombinant surface proteinB. Capsular polysaccharideC. Live attenuated bacteriaD. Killed bacteriaE. Inactivated toxinF. Synthetic oligopeptidesExplanation:There are more than 80 serotypes of S. pneumoniae based on variants of thecapsular polysaccharide. The diversity of serotypes makes vaccine development acomplex task. In adults, S. pneumoniae types 1-8 are responsible about 75% of thetime. The 23-valentpneumococcal polysaccharide single-dose vaccine isrecommended for all adults over age 65 and for other patients at high risk forpneumococcal sepsis (e.g. HIV patients asplenic patients, chronic obstructivepulmonary disease patients, and immunosuppressed patients). It is 50-90%efficacious (Choice B).There is also a 7-valent conjugated vaccine available for use in children less than 2-years-old, which is about 90% efficacious in these patients. The conjugated vaccinecontains polysaccharide antigens that are protein-coupled in order to stimulate theT-cell dependent immune (memory) response.The N. meningitidis and H. influenzae vaccines are other examples of polysaccharidevaccines.(Choice A) The Hepatitis B vaccine is a recombinant surface protein vaccine.(Choice C) Live attenuated bacterial vaccines include the BCG vaccine used outsideof the United States to immunize against tuberculosis and the typhoid vaccine(against Salmonella typhi). Live attenuated vaccines are very effective at inducingimmunity because the organisms are actively growing within the inoculated host.The risk associated with these vaccines is the live organism’s potential to revert to avirulent strain. Live attenuated vaccines are more commonly used for viruses, andinclude the vaccines for measles mumps, rotavirus, and Varicella-zoster, as well asthe Sabin polio vaccine.(Choice D) Killed bacteria vaccines include those for anthrax (Bacillus anthracis),cholera (Vibrio cholera), and pertussis (Bordetella pertussis) and plague (Yersiniapestis). Killed vaccines usually require multiple inoculations in order to induceimmunity, but they do not possess the risk of virulent reactivation. This vaccinationmethod is also more commonly used in viral vaccines, including the hepatitis A,influenza, rubella, rabies and Salk polio vaccines.(Choice E) Inactivated toxin vaccines include the diphtheria and tetanus vaccines.Inactivated toxin vaccines allow the body to immunologically recognize the toxin andinactivate it by antibody binding.(Choice F) Synthetic oligopeptides are presently an experimental mode ofvaccination. Researchers are analyzing the structures of proteins expressed byinfectious vectors and attempting to identify oligopeptide epitopes that could besynthetically produced and used to generate an immune response. As yet novaccines using this mechanism have been produced.
Educational Objective:The pneumococcal polysaccharide vaccine is recommended for all adults over 65years of age and for patients with COPD, asplenia, or immunosuppression.Vaccination does not completely prevent pneumonia, as this vaccine only containsantigen from 23 of the more than 80 different capsular serotypes known. The adultpneumococcal vaccine is an unconjugated polysaccharide vaccine that, unlike theinfant vaccine, does not stimulate a T-helper response.
Q NO 41: A 6-year-old male is brought to the pediatric emergency room with fever and sore throat. The parents tell you that the child has not received any immunizations. Physical exam reveals a grey pharyngeal exudate and Gram stain shows scant Gram positive organisms. Which of the following culture types would facilitate the growth of this organism?A. MacConkey agarB. Thayer-Martin VON mediumC. Blood agar containing bile and hypertonic salineD. Cysteine-tellurite agarE. Bordet-Gengou mediumExplanation:Corynebacteria (koryne, club) are Gram positive catalase-positive, aerobic orfacultatively anaerobic club-shaped rods. The genus is composed of the speciesCorynebacterium diphtheriae and the non diphtheria corynebacteria, also known asdiphtheroids. (Once thought to be clinically insignificant diphtheroids are nowrecognized as pathogens that cause diseases like septicemia, urinary tract infectionserythrasma and endocarditis in immunocompromised hosts.)C. diphtheriae will grow on cysteine-tellurite agar as dark black slightly iridescentcolonies. It can also be cultured in Loffler’s medium where it will develop cytoplasmicmetachromatic granules (visualizable after staining with an aniline dye such asmethylene blue). Because culturing the organism may take days and becausediphtheria has high mortality that warrants immediate treatment more rapiddiagnostic mechanisms such as the immunochromatographic strip assay are beingdeveloped.(Choice A) MacConkey agar is used to grow many of the enteric bacteria. MacConkeyis a bile salt-containing agar that restricts the growth of most Gram positiveorganisms.(Choice B) Thayer-Martin VCN medium will encourage growth of Neisseria specieswhile prohibiting growth of other organisms. This heated blood agar, or chocolateagar is supplemented with the antimicrobial agents Vancomycin, Colistin(polymyxin), and Nystatin (VCN) which restrict the growth of Gram positiveorganisms Gram negative organisms other than Neisseria and yeast respectively.(Choice C) Blood agar containing bile and hypertonic saline can be used to cultureenterococci and to differentiate enterococci from the non enterococcal Group DStreptococci. The enterococci include E. faecalis and E. faecium and are able to growin the presence of both bile salts and 6.5% hypertonic saline. The non enterococciinclude Streptococcus bovis and Streptococcus equinus. Non enterococcal Group Dstreptococci grow in the presence of bile but NOT in the presence of hypertonicsaline.(Choice E) Bordet-Gengou medium is used to culture the veri sensitive Bordetellapertussis, the causative agent in whooping cough.Educational Objective:C. diphtheriae is cultured on cysteine-tellurite agar. The resultant colonies are blackin color. The bacterium produces intracellular polyphosphate granules calledmetachromatic granules that can be detected on microscopy after methylene bluestaining.
Q NO 42: A 7-year-old child with a history of recurrent granulomatous skin infections and a prior episode of Aspergillus pneumonia undergoes a partial hepatectomy to treat a poorly draining liver abscess. The patient is thought to have a mutation of a structural component of a neutrophil oxidase. This child also has an increased vulnerability to infections caused by:A. Pseudomonas cepaciaB. Mycobacterium tuberculosisC. Cryptococcus neoformansD. Herpes simplex type 1E. Streptococcus pyogenesF. Giardia lambliaG. Corynebacterium diphtheriaeExplanation:This patient has chronic granulomatous disease (COD), a condition caused bymutations in neutrophil NADPH oxidase. Patients with COD are at increased risk forinfections caused by• Staphylococcus aureus• Pseudomonas cepacia (Burkholderia cepacia)• Serratia marcescens• Nocardia species• Aspergillus speciesThese organisms are all catalase positive. Catalase decomposes H202 (2 H202 — +2 H20). In COD patients the production rate of H202 (and the downstreammicrobicidal HOCL) is impaired. It appears that catalase positivity is necessary butnot sufficient for opportunistic infectivity in COD, since the risk of infection withother catalase positive microbes (such as Mycobacterium tuberculosis, Cryptococcusneoformans, and Corynebacterium diphtheriae) is not increased in COD.(Choice E) Streptococci are catalase negative bacteria. COD patients are predisposedto infections with catalase positive organisms.Educational Objective:Chronic granulomatous disease (COD) results from a genetic defect in NADPHoxidase. Normally, NADPH oxidase participates in the killing of microbes withinneutrophil phagolysosomes. Patients with COD develop recurrent pulmonary,cutaneous lymphatic and hepatic infections with a tendency toward granulomaformation, usually beginning in childhood. These infections are predominantly causedby:• Staphylococcus aureus• Pseudomonas cepacia (Burkholderia cepacia)• Serratia marcescens• Nocardia species• 4spergillus species
Q NO 43: A 23-year-old male is being evaluated for persistent cough and a pulmonary infiltrate detected on chest X-ray. 3 ml of this patient’s blood is added to an anticoagulated tube and placed into iced water. Several minutes later clumping is detected inside the tube, but it rapidly un coagulates when the tube is warmed while being held it in the observer’s hand. Which of the following organisms is most likely responsible for this patient’s condition?A. Streptococcus pneumoniaeB. Klebsiella pneumoniaeC. Haemophilus influenzaeD. Mycobacterium kansasiiE. Legionella pneumophilaF. Coxiella burnetiiG. Mycoplasma pneumoniaeH. Coccidioides immitisI. Histoplasma capsulaturnJ. Pneumocystis cariniiExplanation:The question stem is describing the effect of cold agglutinins. As their name implies,cold agglutinins cause the agglutination, or clumping, or red blood cells when asample of blood containing cold agglutinins is chilled. Cold agglutinins are antibodiesthat are produced in response to Mycoplasma pneumoniae infection. Theseantibodies are directed against antigens in the cell membrane of M. pneumoniae thathappen to be homologous to antigens that are present on the surface of humanerythrocytes. The test described can be easily done at bedside with blood drawn intoan EDTA-containing tube and a cup of ice. These cold agglutinins are responsible forthe transient anemia that can be documented in many patients with a M.pneumoniae infection. Cold agglutinins are also associated with Epstein-Barr virusinfection and hematologic malignancies in addition to infection with Mycoplasmapneumoniae.Educational Objective:Infection with Mycoplasma pneumoniae can result in the formation of coldagglutinins. Other illnesses resulting in cold agglutinin formation include EBVinfection and hematologic malignancy. Cold agglutinins are antibodies specific for redblood cells that only cause agglutination, or clumping, of red blood cells at lowtemperatures.
Q NO 44: Bacteria are injected into the skin of several healthy volunteers as part of an experiment. Over several weeks, the bacteria migrate slowly through the skin from the site of injection outward. On physical examination, each patient develops a flat red skin lesion with a central clearing. Which of the following bacteria was most likely injected?A. Mycobacterium scrofulaceumB. Treponema pallidumC. Leptospira interrogansD. Borrelia burgdorferiE. Rickettsia rickettsiaeF. Bartonella henselaeExplanation:These cutaneous lesions are consistent with erythema chronicum migrans (ECM) theclassic initial skin lesion of Lyme disease. ECM occurs at the site of Borreliaburgdorferi (Choice D) inoculation by an Ixodes tick bite. ECM begins as anerythematous macule that enlarges with an advancing erythematous border andcentral clearing. The classic lesion is erythematous (red) and ring-shaped (annular).Often the central clearing does not appear, and the rash remains an erythematousmacule or patch.(Choice A) Mycobacterium scrofulaceum is the etiologic agent of scrofula, a diseasecharacterized by lymphadenitis (usually cervical lymphadenitis) that occurs withgreatest frequency in children.(Choice B) Treponema pallidum is the etiologic agent of syphilis. Syphilis causes apainless ulceration, or chancre, at its site of inoculation. In secondary syphiliscondyloma lata and a generalized macular eruption may appear.(Choice C) The spirochete Leptospira interrogans is the etiologic agent ofleptospirosis. L. interrogans produces no characteristic cutaneous manifestations.Infection is usually asymptomatic and self-limited, though serious cases canprogress to Weil’s syndrome. In Weil’s syndrome hepatic dysfunction produces aconjugated hyperbilirubinemia, renal dysfunction, thrombocytopenia, and bleeding.(Choice E) Rickettsia rickettsia is the etiologic agent of Rocky Mountain spotted fever(RMSF). RMSF is a tick- borne illness characterized by a palmoplantar erythematousmacular or petechial eruption that spreads proximally to eventually involve thetrunk. Patients also experience headache, fever and conjunctival hyperemia.Diagnosis is based on clinical findings and patient history prompt treatment withdoxycycline is required.(Choice F) Bartonella henselae is the Gram negative etiologic agent of cat scratchfever. Cat scratch fever, as the name implies, occurs after a cat scratch or bite.Clinical manifestations include regional lymphadenopathy, malaise and fever. Otherthan regional lymphadenopathy, B. henslae infection is not associated with anycharacteristic cutaneous lesions.Educational Objective:The characteristic cutaneous lesion in B. burgdorferi infection (Lyme disease) iserythema chronicum migrans (ECM). Typically, ECM begins as an erythematousmacule at the site of the inoculating tick bite. The macule then spreads outwardleaving a zone of central clearing. ECM is characteristic of the first stage of Lymedisease, but can recur at various distant skin sites in the second stage of Lymedisease as well.
Q NO 45: A 7-year-old boy is brought to your office with blisters on his face. Some of the blisters have broken and are covered with golden yellow crusts. Exudate microscopy reveals Gram-positive cocci in chains. Which of the following would be a component of the clinical syndrome that may follow such an infection?A. Joint pain and eve rednessB. Fatigue and heart murmursC. Face puffiness and dark urineD. Bilateral facial nerve palsyE. Abdominal pain and jaundiceExplanation:Staphylococcus aureusand Streptococcus pyogenes(so called pyogenic cocci) cause prima diseases of theskin and subcutaneous tissues, frequently infecting wounds, abrasions and burns,Impetigo, a vesicular, blistering eruption eventually leading to formation of a goldenyellow crust, is usually seen in children and newborns, frequently occurs periorally,and can be caused by either Staphylococcus aureus and/or Streptococcus pyogenes.Acute rheumatic fever (ARE) and Acute Post Streptococcal Glomerulonephritis(APSGN) are the late sequelae of untreated or partially treated S. pyogenes (GroupA Strep) infections. APSGN can follow a streptococcal skin infection (impetigo) or astreptococcal pharyngeal infection. If APSGN occurs, it will occur 1-5 weeks after theonset of the streptococcal infection. Rheumatic fever, on the other hand, isassociated only with Group A Streptococcal (GAS) throat infection.Hypertension hematuria, nephritic range proteinuria, and RBC casts in the urinefollowing a GAS infection suggest acute post streptococcal glomerulonephritis.Patients frequently present with facial edema and dark colored (cola colored) urine(Choice C). The renal damage is due to immune complex deposition on theglomerular basement membrane and activation of complement. Complementactivation is responsible for the massive inflammatory response and glomerularbasement membrane structural damage seen in APSGN.(Choice A) Joint pain and eye redness can occur with many conditions includingSjogren syndrome lupus and Reiter syndrome. Reiter syndrome is an HLA-B27related illness that occurs most classically in relation to an episode of Chlamydiatrachomatis urethritis. It is an inflammatory arthritis that usually affects large jointsand causes uveitis and conjunctivitis. The triad of arthritis, uveitis/conjunctivitis andurethritis defines Reiter syndrome.(Choice B) Fatigue and heart murmurs following a GAS pharyngeal infection can bedue to acute rheumatic fever. When rheumatic fever occurs, it is usually 4-6 weeksfollowing an untreated episode of streptococcal pharyngitis; it DOES NOT occur inrelation to streptococcal skin infections.(Choice D) Bilateral facial nerve palsy is extremely rare. Infectious causes mostclassically include Lyme disease (Borrelia burgdorferi) and, less commonly, HIV.(Choice E) Abdominal pain and jaundice in a child can indicate acute viral hepatitismost likely due to HepatitisA. Hepatitis A is transmitted by the fecal-oral route, and outbreaks have beendescribed in child care settings.Educational Objective: Rheumatic fever and acute post-streptococcalglomerulonephritis are the late sequelae of Group A Streptococcal (Streptococcuspyogenes) infections. Post-streptococcal glomerulonephritis can follow either a skininfection (impetigo) or an episode of streptococcal pharyngitis, whereas rheumaticfever is associated only with streptococcal throat infection.
Q NO 46: A toxic substance produced by C. perfringens induces massive hemolysis and tissue necrosis when injected into mice. The lethal effect observed in the experiment correlates with the substance’s ability to splitA. CollagenB. Hyaluronic acidC. PhospholipidsD. CarbohydratesE. PlasminogenExplanation:Lecithinase is the main toxin of C. perfringens; its concentration correlates with itslethal and necrotic effects. Lecithinase, also known as phospholipase C or alpha toxinis an enzyme that catalyzes the splitting of phospholipid molecules. (Recall thathuman phospholipase A2 is the enzyme that catalyzes arachidonic acid release fromphospholipid cell membranes in the first step of leukotriene, thromboxane, andprostaglandin synthesis.) Phospholipase C hydrolyzes lecithin-containing lipoproteincomplexes in cell membranes causing cell lysis (including RBC hemolysis), tissuenecrosis and edema. C. perfringens has atleastl2toxins of which Alpha toxin is themost injurious.(Choice D) C. perfringens uses carbohydrates for energy. Its rapid metabolism ofmuscle tissue carbohydrate produces significant amounts of gas, which can bedemonstrated radiographically by either plain film X-ray or CT scan.(Choice E) Plasminogen activators like streptokinase, urokinase and tissueplasminogen activator (tPA) convert plasminogen to plasmin. Of the three enzymesmentioned, only streptokinase is a bacterial product, and as the name implies, itisan exotoxin released by Streptococcus pyogenes (Group A Streptococcus).Educational Objective:Lecithinase, also known as alpha toxin, is the main toxin produced by C. perfringens.Its function is to degrade lecithin, a component of cellular phospholipid membranes,leading to membrane destruction, cell death and widespread necrosis and hemolysis.
Q NO 47: A 34-year-old immigrant from Africa has patchy areas of skin anesthesia and hypopigmentation on his upper extremities. Nerve biopsy evaluated under light microscopy shows many bacteria invading Schwann cells. This patient’s disease is most likely caused by:A. Borrelia burgdorferiB. Treponema pallidiumC. Corynebacteria diphtheriaeD. Mycobacteria lepraeE. Campylobacter fetusExplanation:Leprosy, or Hansen disease, is a deforming infection primarily of the skin and nervesthat is caused by Mycobacterium leprae. Transmission is believed to occur throughthe respirators’ route, although direct cutaneous contact has not been excluded as amode of transmission. Infection has been also associated with armadillo contact inthe southwest United States. Leprosy has a wide range of clinical manifestations thatvary depending on the strength of the cell-mediated immune response to theorganism.The most severe form of leprosy is termed “lepromatous leprosy” and occurs inpatients with a weak cell-mediated (Th1) immune response. Without an appropriatecell-mediated response macrophages are never given the signal to kill themycobacterial organisms. As a result M. leprae multiplies and disseminates widely.M. leprae grows best at temperatures that are slightly lower than core bodytemperature, which partially explains why the features of leprosy are primarilyobserved in the skin superficial nerves, eyes and testes. Lepromatous leprosyclinically manifests as diffuse skin thickening, cutaneous hypopigmentation inplaques (often accompanied by hair loss), leonine facies, paresis and regionalanesthesia of motor and sensory nerves, and testicular destruction and blindness.The least severe form of leprosy is often self-limited and is called “tuberculoidleprosy.” In this subtype, the mycobacterial infection is limited by an intact cell-mediated immune system. Mild skin plaques develop that are associated withhypopigmentation, hair follicle loss, and focally decreased sensation.Features intermediate between the tuberculoid and lepromatous forms are oftenseen, demonstrating the true spectrum of this disease.(Choice A) Borrelia burgdorferi is the spirochete responsible for Lyme disease.Symptoms of Lyme disease involve a characteristic skin rash (erythema chronicummigrans, which occurs most frequently at the site of the tick bite) fever myalgiasand malaise. Systemic disease can progress to cause arthritis, facial paresis, and/orcardiac inflammation (which may be associated with conduction abnormalities).Prolonged untreated disease can lead to CNS effects similar to those of tertiarysyphilis.(Choice B) Treponema pallidum is the spirochete responsible for syphilis. Syphilis isa sexually transmitted disease that initially causes a painless ulceration (chancre) atthe site of inoculation, most commonly the genitalia. Systemic illness is described assecondary syphilis and results in the diffuse eruption of erythematous macules overthe entire body, including the palms and soles (which differentiate it from manyother rashes) and the formation of condyloma lata. Tertiary syphilis results ingummas of the skin and bone ascending aortitis, and neurosyphilis.(Choice C) Corynebacterium diphtheriae is the Gram-positive rod responsible fordiphtheria.
(Choice E) Campylobacter fetus is a Gram-negative rod responsible for mild enteritisin immunocompetent patients and mild systemic bacteremic illness inimmunocompromised patients.Educational Objective:Leprosy, or Hansen disease, is a systemic illness caused by Mycobacterium leprae.The severity of disease depends on the strength of the cell-mediated immuneresponse, with tuberculoid leprosy the milder form and lepromatous leprosy themore severe form.
Q NO 48: A 74-year-old previously healthy male comes to his physician’s office complaining of abrupt on set fever, headache, myalgias, malaise, cough and throat pain. His two granddaughters missed several days of school because of similar symptoms. Examination demonstrates mild hyperemia of the throat without any exudate, and the patient is sent home on conservative management. Five days later, he is admitted to the hospital with progressive dyspnea, chest pain, and productive cough. Which of the following pathogens is most likely to be isolated from this patient’s sputum?A. Listeria monocytogenesB. Klebsiella pneumoniaeC. Staphylococcus aureusD. Nontuberculous mycobacteriaE. CytomegalovirusExplanation:This patient’s presenting signs and symptoms and report of similarly ill householdchildren are consistent with influenza infection. Outbreaks of influenza A can affect50-75% of school-aged children, many of whom then spread the virus to familymembers. Individuals infected with influenza A tend to experience abrupt onsetfever, headache myalgia, and malaise: signs and symptoms gradually improve overa period of two to five days.A subset of patients stricken by influenza go on to develop secondary bacterialpneumonia characterized by recurrent fever, dyspnea, and productive cough. Theelderly are particularly at risk for this complication. Physical examination and chestradiograph demonstrate pulmonary consolidation. Patients recently infected withinfluenza are vulnerable to secondary bacterial infection because of virally-induceddamage to the mucociliary clearance mechanisms of the respiratory epithelium. Inorder, the pathogens most often responsible for secondary bacterial pneumonia areStreptococcus pneumoniae, Staphylococcus mucus, and Haemophilus influenzae.(Choice A) Listeria monocytogenes is an occasional cause of septicemia and purulentmeningitis in neonates.(Choice B) Klebsiella pneumoniae is most commonly responsible for nosocomialurinary tract infections nosocomial pneumonia, and pneumonia in alcoholics and IVdrug abusers.(Choice D) Mycobacterium avium intracellulare causes disseminated disease in AIDS.Mycobacterium kansasii may yield pulmonary tuberculosis-like symptoms.Mycobacterium leprae is responsible for cutaneous leprosy. Mycobacteriumscrofulaceum causes cervical lymphadenitis in children.(Choice E) Cytomegalovirus (CMV) may cause pneumonia particularly in theimmunocompromised (eg, those with HIV infection).Educational Objective:Patients older than 65 are particularly prone to developing secondary bacterialpneumonia after influenza infection. In order, the pathogens most often responsiblefor secondary bacterial pneumonia are Streptococcus pneumoniae, Staphylococcusaureus, and Haemophilus influenzae.
Q NO 49: A 22-year-old male ingests a solution containing 13C-labeled urea. He is then asked to blow into a tube, and the labeled carbon is detected in his breath samples. This test is most likely part of the evaluation for which of the following conditions?A. BronchiectasisB. Pulmonary fibrosisC. Congenital heart diseaseD. Chronic hepatitisE. Duodenal ulcerF. Acute pancreatitisG. Chronic diarrheaExplanation:The test described is a screening assay for the presence of urease activity, anindirect means of detecting the presence of Helicobacter pylori, a major cause ofduodenal ulcer. Culturing the organism from gastric biopsy specimens is consideredthe definitive confirmatory test. The noninvasive urease breath test involvesconsuming a solution containing isotopically-labeled urea. When present urease (aproduct of H. pylon) degrades the urea into carbon dioxide and ammonia. Theisotopically-labeled carbon dioxide is absorbed into the bloodstream and exhaled inthe patient’s breath. Typically, breath samples are collected 30 minutes after thelabeled urea is ingested. This test has excellent sensitivity and specifically for boththe initial diagnosis of H. pylon infection and for monitoring treatment success.Antibiotic or proton pump inhibitor use during the 2-4 weeks prior to the test maycause false negative results.(Choice A) High-resolution chest CT is the test of choice for diagnosingbronchiectasis.(Choice B) High resolution CT scan chest X-ray, pulmonary function testing, lungbiopsy, and serologies may all play a role in diagnosing pulmonary fibrosis, but noneis considered a gold standard.(Choice C) Congenital heart diseases (e.g. patent foramen ovale, ventricular septaldefect) are most commonly diagnosed by echocardiography.(Choice D) Viral hepatitis is diagnosed when viral components and antibodies againstthe hepatitis virus are detected in the blood.(Choice F) Acute pancreatitis is usually diagnosed by correlating a patient’s clinicalpresentation (i.e. the characteristic epigastric pain boring through to the back) withelevated amylase and lipase levels.Educational Objective:The urease breath test is used to noninvasively detect H. pylon infection. The patientconsumes 13C-labeled urea and his breath is then monitored for the presence of13C-labeled carbon dioxide which would indicate the presence of the H. pylonproduct urease in the stomach.
Q NO 50: A 3-month old infant is irritable, feeds poorly and frequently vomits. His current weight is at the 45th percentile and his head circumference as at the 96th percentile. Funduscopy reveals white-yellow chorioretinal lesions in both eyes. Head CT shows enlarged ventricles and scattered intracranial calcifications. Which of the following is the most likely cause of this patient’s condition?A. Chromosomal abnormalityB. Single gene diseaseC. In-utero infectionD. Intrapartum infectionE. Postpartum infectionExplanation:Hydrocephalus, intracranial calcifications and chorioretinitis form the classic triad ofcongenital toxoplasmosis. Hydrocephalus occurs due to CNS inflammation and isevidenced by macrocephaly and enlargement of the ventricles. Chorioretinitis srefers to inflammation of the choroids and the retina that can leave cotton-likewhite/yellow scars on the retina visible on funduscopy. Affected neonates also havehepatosplenomegaly, rash and multiple neurological abnormalities such as seizures,altered muscle tone and ocular movement defects. Occasionally microcephaly occurswhen hydrocephalus is not severe.Congenital toxoplasmosis is transmitted transplacentally. The fetus is affected only ifthe mother is infected with toxoplasmosis during the first six months of pregnancy.As the majority of healthy individuals are exposed to Toxoplasma early in childhood,most adults are immune and primary infection in pregnancy is rare. Pregnantwomen, however, should be warned not to handle cat litter in order to preventcontact with Toxoplasma which is often found in cat feces.(Choice D) Infection with herpes simplex is acquired by a neonate during delivery(intrapartum). Ophthalmia neonatorum refers to neonatal conjunctivitis caused by anumber of agents such as Chlamydia, Neisseria (which can cause blindness), andviruses; these infections are acquired during birth. Group B streptococcal sepsis isalso acquired during birth.(Choice E) Postpartum infections include any infections acquired after birth and arenumerous.Educational Objective:Congenital toxoplasmosis is a transplacental infection (acquired in utero). Its classictriad includes hydrocephalus, intracranial calcifications and chorioretinitis. Expectingmothers should avoid cat feces to help prevent exposure to Toxoplasma.