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  • 1. CHAPTER 56 CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS David H. Walker, Gail L. Woods, Michael B. Smith CHLAMYDIAL INFECTIONS, 1065 African Tick Bite Fever, Laboratory Diagnosis, 1075 Structure, 1066 Boutonneuse Fever, and Other Treatment, 1075 Replication, 1066 Spotted Fevers, 1070 Infections Caused by Organisms Chlamydia trachomatis, 1066 Rickettsialpox, 1072 of the Genus Bartonella, 1075 Epidemiology, Pathology, and Flea-borne Spotted Fever, 1072 Structure and Function, 1075 Clinical Manifestations, 1066 Murine Typhus and Louse-borne Cat Scratch Disease, Bacillary Chlamydophila (formerly Typhus, 1072 Angiomatosis, and Bacillary Chlamydia psittaci), 1067 Rickettsiae as Agents of Peliosis, 1075 Epidemiology, 1067 Bioterrorism, 1072 Trench Fever and Bacillary Pathogenesis and Laboratory Diagnosis, 1072 Angiomatosis, 1076 Pathology, 1067 Treatment, 1073 Oroya Fever and Verruga Clinical Manifestations, 1067 Scrub Typhus Caused by Orienta Peruana, 1076 Chlamydophila (formerly tsutsugamushi, 1073 Laboratory Diagnosis, 1076 Chlamydia pneumoniae), 1067 Infections Caused by Organisms Treatment, 1076 Epidemiology, 1068 of the Genera Ehrlichia and MYCOPLASMAL Anaplasma, 1073 Pathogenesis, 1068 INFECTIONS, 1076 Structure and Function, 1073 Clinical Manifestations, 1068 Mycoplasma pneumoniae, 1076 PART 7 Human Monocytotropic Laboratory Diagnosis, 1068 Epidemiology, 1076 Ehrlichiosis, 1073 Chlamydia trachomatis, 1068 Pathogenesis and Human Infection With Ehrlichia Chlamydophila psittaci, 1069 Pathology, 1076 ewingii, 1074 Chlamydophila Clinical Manifestations, 1077 Human Granulocytotropic pneumoniae, 1069 Anaplasmosis, 1074 Genital Mycoplasmas, 1077 Treatment, 1070 Laboratory Diagnosis, 1074 Epidemiology, 1077 RICKETTSIAL INFECTIONS, 1070 Treatment, 1074 Clinical Manifestations, 1077 Infections Caused by Organisms Infections Caused by Coxiella Laboratory Diagnosis, 1077 of the Genus Rickettsia, 1070 burnetii, 1074 Mycoplasma pneumoniae, 1077 Structure and Function, 1070 Structure and Function, 1074 Genital Mycoplasmas, 1078 Rocky Mountain Spotted Q Fever, 1075 Treatment, 1078 Fever, 1070 SELECTED REFERENCES, 1078 KEY POINTS • The clinicoepidemiologic diagnosis of cat scratch disease can be confirmed serologically by antibodies to Bartonella henselae or by• Chlamydia trachomatis is the most common bacterial cause of sexually polymerase chain reaction testing of lymph node aspirates. transmitted disease in the United States. • Pneumonia due to Mycoplasma pneumoniae is often diagnosed on the• The most sensitive method for detecting C. trachomatis is nucleic acid basis of clinical manifestations alone. Definitive diagnosis requires amplification. detection of specific immunoglobulin (Ig)M, a fourfold change in IgG• Chlamydophila pneumoniae (formerly Chlamydia pneumoniae) is antibody titer between acute and convalescent serum specimens, or detection of nucleic acid in sputum or other respiratory specimens by responsible for at least 10% of community-acquired pneumonias. Infection is most often diagnosed serologically. nucleic acid amplification.• Treatable rickettsial infections, including life-threatening Rocky Mountain spotted fever, boutonneuse fever, epidemic typhus, murine typhus, scrub typhus, human monocytotropic ehrlichiosis, and human Human infections caused by chlamydias, rickettsiae, and mycoplasmas are granulocytotropic anaplasmosis, are seldom diagnosed serologically discussed separately because the responsible pathogens differ from most during the acute stage of illness owing to absence of an early other bacteria in several ways: The organisms are smaller, the structure of antibody response. their cell walls is different, and chlamydias and many rickettsiae are obli-• Immunohistochemistry and molecular diagnostics are effective in gately intracellular parasites. diagnosing rickettsioses and ehrlichioses, respectively, but are not generally available. CHLAMYDIAL INFECTIONS• Q fever endocarditis is a chronic infection that usually is diagnosed by The chlamydias have a tropism for columnar epithelial cells. They have a detecting a high titer (≥1 : 800 by immunofluorescent antibody assay) cell wall similar to that of gram-negative bacteria; they contain both deoxy- of antibodies against Coxiella burnetii phase I antigen. ribonucleic acid (DNA) and ribonucleic acid (RNA), have prokaryotic 1065
  • 2. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS TABLE 56-1 enters the host cell, changes in its cell wall result in a transition to the Features Useful for Differentiating Species of Chlamydia and reticulate body and subsequent initiation of DNA, RNA, and protein Chlamydophila Pathogenic for Humans synthesis and its division by binary fission. Host cell mitochondria migrate to and are positioned against the enlarging endosome, allowing the reticu- SPECIES late body to utilize host cell ATP. Reticulate bodies begin to reorganize 18–24 hours after infection, and, presumably when nutrients are depleted, Chlamydia Chlamydophila Chlamydophila they mature into elementary bodies, which are released from the host cell. Parameter trachomatis psittaci pneumoniae Cells infected with C. psittaci usually are severely damaged, and the organ- Sulfa susceptibility Susceptible Resistant Resistant isms are released by cell lysis within 48 hours. In contrast, the inclusion of C. trachomatis appears to be extruded by fusion of the inclusion mem- Glycogen staining Positive Negative Negative brane with the plasma membrane 72–96 hours after infection, leaving a of inclusion lesion in the surviving host cell membrane. Elementary body Round Round Pear-shaped or shape round CHLAMYDIA TRACHOMATIS C. trachomatis is the most common cause of sexually transmitted disease in the United States, and in trachoma-endemic regions of the Middle East, ribosomes, and synthesize their own proteins, nucleic acids, and lipids; they sub-Saharan Africa, and Asia, it is the primary infectious cause of blindness. divide by binary fission; and they are susceptible to particular antibiotics. The disorder is endemic in more than 50 countries, and estimates indicate Unlike most bacteria, the chlamydias are “energy parasites”; they lack that more than 3 million people are affected, with over a third having cytochromes and so cannot synthesize high-energy adenosine triphosphate progressed to blindness (Burton, 2009). (ATP) metabolites. For this reason, they are obligate intracellular bacteria and cannot replicate outside cells. The chlamydias are classified in the order Chlamydiales, family Chla- Epidemiology, Pathology, and mydiaceae, the only family that contains human pathogens (Everett, 1999). Clinical Manifestations Two genera and three species are pathogenic for humans: Chlamydia tra- Humans are the only known natural host for all strains of C. trachomatis. chomatis, Chlamydophila (formerly Chlamydia) psittaci, and Chlamydophila The clinical manifestations and organ specificity of human infections with (formerly Chlamydia) pneumoniae. Features useful for differentiating the C. trachomatis are determined by both the mechanism of transmission and three species are shown in Table 56-1. These genera also contain six other the properties of the infecting strain. Epidemiologically, C. trachomatis species that have not been associated with infection in humans. There are infections are divided into three categories: classic trachoma, sexually two biovars of C. trachomatis: lymphogranuloma venereum (Biovar LGV) transmitted infections of adults, and perinatal ocular and respiratory tract56 and trachoma (Biovar trachoma), which preferentially infect humans. infections. Biovar LGV contains four serovars (L1, L2, L2a, and L3), and 15 serovars Classic trachoma is an important cause of blindness in areas where are included in Biovar trachoma: A, B, Ba, and C are associated with tra- public sanitation is inadequate and personal hygiene poor (Solomon, choma, whereas D–K, Da, Ia, and Ja are associated with genital infections. 2004). The disease is due to repeated infections of the conjunctiva, result- Mouse and hamster isolates that previously made up the third biovar of ing in a pathologic sequence over time of follicular conjunctivitis, subepi- C. trachomatis have been reclassified as a new species, Chlamydia muridarum thelial scarring, contraction of the scar resulting in turning inward of the (Everett, 1999). eyelid (entropion), rubbing of the eyelashes on the cornea (trichiasis) with subsequent corneal injury, and corneal scarring with opacification and reduced vision. Typically, acute infection is transmitted among children via STRUCTURE fingers, fomites, and probably flies, and most children become chronically Two morphologically distinct forms of chlamydia are recognized. The infected within a few years of birth. Conjunctival scarring usually becomes elementary body is a dense, spherical form, 0.2–0.4 μm in diameter, that evident by the second or third decade of life, and blindness can occur contains prokaryotic ribosomal RNA and has a rigid cell wall caused by anywhere from 10–40 years after the first infection (Dean, 2008). It is extensive disulfide cross-linking of cell wall proteins. It is the infectious interesting to note that a recent study using molecular methods on infected form of the organism, capable of limited extracellular survival. The reticu- patients in a trachoma-endemic location demonstrated that other species late body, 0.6–1.0 μm in diameter, is the intracellular, metabolically active of the Chlamydiaceae, C. psittaci and C. pneumoniae, may also be involved form, incapable of surviving outside cells. The closed circular DNA of both in the pathogenesis of trachoma (Dean, 2008). forms is compactly organized in a central nucleoid and has a genome of C. trachomatis–induced sexually transmitted infections of adults include 1.0–1.2 million nucleotide base pairs. LGV and urethritis/cervicitis and associated complications. LGV is Two components of the outer membrane of the chlamydial outer mem- endemic in Asia, Africa, and South America. In the United States, approxi- brane complex have diagnostic importance. The most prominent is the mately 500 cases are reported each year; the disease affects males more major outer membrane protein (MOMP), a transmembrane protein with frequently than females and is most common in persons of low socio- serovar-, species-, genus-, and family-reactive epitopes defined by mono- economic status living in the southeastern states, in men who have sex clonal antibodies. Infection with chlamydias induces MOMP-specific anti- with men, and in persons who have visited LGV-endemic countries bodies, but their role in protective immunity is unclear. The chlamydial outside the United States. LGV is transmitted sexually, although trans- outer membrane complex also contains a lipopolysaccharide (LPS) antigen, mission by fomites and by aerosols produced during laboratory accidents which is the major antigen detected in genus-specific serologic tests for has caused pneumonitis, pleural effusions, and mediastinal or hilar lymph- chlamydial infection. Monoclonal antibodies and monospecific polyvalent adenopathy (Jones, 2000). Reservoirs of infection probably are persons antisera to the LPS or MOMP are used in direct fluorescent antibody with asymptomatic or ignored symptomatic urethral, cervical, or anorectal (DFA) tests and enzyme immunoassays (EIAs) to detect chlamydial antigen infection. in clinical specimens. LGV is the only infection caused by C. trachomatis that produces mul- tisystem involvement and constitutional manifestations. During the primary phase, a small, painless vesicle or a nonindurated papule or ulcer REPLICATION develops, often on the external genitalia, 3 days to 3 weeks after exposure, Chlamydias replicate in the cytoplasm of infected host cells. The develop- and heals quickly without scarring. If transmission is rectal, an acute proc- mental cycle begins with attachment of the elementary body to a microvil- titis is often the first manifestation. An outbreak of LGV proctitis in men lus on a susceptible columnar cell via heparin bridges. The elementary who have sex with men was first noticed in Europe at the beginning of this body travels down the microvillus and localizes in indentations of the host decade and is due to infection with a unique LGV variant (labeled “L2b”) cell plasma membrane. There, the chlamydia enters the host cell in an (Spaargaren, 2005). Genomic similarity to isolates obtained from patients endosome, where C. psittaci, C. pneumoniae, and C. trachomatis remain in the early 1980s in the United States suggests a silent ongoing epidemic during their intracellular development. Endosomes containing elementary in this population caused by this unique variant (Spaargaren, 2005). The bodies of C. psittaci do not become acidified or fuse with cellular lysosomes; secondary stage, characterized by suppurative regional lymphadenopathy, those containing C. trachomatis elementary bodies fuse with one another fever, chills, anorexia, headache, myalgias, and arthralgias, begins 2–6 and perhaps with lysosomes. Within 6–8 hours after the elementary body weeks after exposure. The primary ulcer or papule often resolves before 1066
  • 3. the secondary stage, but an acute proctitis may persist. Histologic examina- CHLAMYDOPHILA (FORMERLYtion of affected lymph nodes shows granulomas surrounding stellateabscesses. Involved lymph nodes become matted and eventually suppurate, CHLAMYDIA PSITTACI)producing draining fistulas that heal with scarring over several months. Pneumonia associated with exposure to birds was described in SwitzerlandFibrosis and resultant abnormal lymphatic drainage are responsible for the in 1879. The disease was rare in the United States and Europe until theurethral or rectal strictures or induration and lymphedema of the genitalia late 1920s, when pet tropical birds became fashionable. The pathogen wasthat develop during the third stage. isolated by Bedson from human and avian tissue in 1930 during an inves- Non-LGV C. trachomatis infection is the most frequent sexually trans- tigation of an outbreak at the London Zoo.mitted disease reported to the Centers for Disease Control and Prevention(CDC). From 1990–2009, the rate increased from 160.2 to 409.2 cases per Epidemiology100,000 population (Centers for Disease Control and Prevention, 2009). Infection caused by Chlamydophila (formerly Chlamydia) psittaci (also calledThe clinical spectrum of sexually transmitted infections due to non-LGV psittacosis, parrot fever, or ornithosis) occurs worldwide. C. psittaci hasstrains of C. trachomatis is similar to disease caused by Neisseria gonorrhoeae seven genotypes (A–F, E/B), all of which are infective for humans. Psitta-(see Chapter 57). In men, C. trachomatis is responsible for 30%–50% of cine birds are considered the major reservoir, but most species of birds cancases of nongonococcal urethritis, but as many as 85%–90% of men who be infected with the organism. Infected birds may be obviously ill and mayharbor C. trachomatis in the urethra are asymptomatic (Peipert, 2003). die of the disease, but frequently they have mild signs such as anorexia,Rarely, urethritis caused by C. trachomatis progresses to epididymitis. diarrhea, lethargy, and ruffled feathers. Human illness is sporadic and hasAmong men who have sex with men, non-LGV strains of C. trachomatis been associated with exposure to parrots, canaries, pigeons, sparrows,have been associated with proctitis. Genital infection with C. trachomatis ducks, cockatiels, fowl (especially turkeys), and occasionally diagnosed more often in women than in men, with a rate of 583.5/100,000 Owners of pet birds account for about half of the 40–60 cases reported inreported for women in the United States in 2008, compared with a rate the United States each year. Pet shop employees, pigeon fanciers, zooof 211.1 for men—a rate difference that is thought, at least in part, to be workers, veterinarians, and others who work with birds are at increasedreflective of the greater number of women who undergo testing (Centers risk of infection. Outbreaks have occurred among poultry processing plantfor Disease Control and Prevention, 2008a). Infection of the endocervix workers, principally among workers who killed the birds and plucked theirwith C. trachomatis is often asymptomatic, but at least one third of women feathers and those who eviscerated carcasses, with a mortality of about 1%,have signs of infection on physical examination. The most common sign even with appropriate therapy (Centers for Disease Control, 1990; Petro-is mucopurulent cervicitis, which can spread to the urethra and urinary vay, 2008). Before the discovery of antibiotics, the mortality rate for humanbladder, resulting in the acute urethral syndrome of abacteriuric pyuria, or infection was 15%–20%. Over the past two decades, the prevalence ofto the endometrium and fallopian tubes, producing endometritis or sal- psittacosis in the United States has declined dramatically as a result ofpingitis. Untreated infections of the upper reproductive tract may progress adding tetracycline to poultry feed, requiring medication of commerciallyto pelvic inflammatory disease or may cause scarring and dysfunction of imported psittacine birds before entering the country and domestic breed- PART 7the oviduct transport system, which could result in infertility, ectopic ing of parakeets.pregnancy, or chronic pelvic pain. Intraperitoneal spread of the infection C. psittaci is present in the blood, tissues, excreta, and feathers ofmay cause acute peritonitis, perihepatitis (Fitz-Hugh–Curtis syndrome), infected birds and may be shed for months after acute infection. Transmis-periappendicitis, or perisplenitis. A portion (1%–5%) of patients with sion to humans occurs via inhalation of infectious aerosols derived fromurogenital infection with C. trachomatis will develop a reactive arthritis that feces, fecal dust, and secretions of C. psittaci–infected birds, but may resultis usually self-limited but may develop a chronic relapsing course (Rihl, from handling contaminated plumage or tissues, from bird bites, or from2006; Carter, 2009). Chlamydial infection in pregnancy has been associ- mouth-to-beak contact. Contact with birds does not have to be close orated with preterm labor, premature rupture of membranes, low birth- prolonged. Person-to-person spread of C. psittaci is rare.weight, neonatal death, and postpartum endometritis. A small percentageof adults with chlamydial genital infections develop inclusion conjunctivitis Pathogenesis and Pathologyfrom autoinoculation. C. psittaci enters the body via the respiratory tract and is transported to the In developed countries, where sexually transmitted infection with macrophages of the liver and spleen, where the organisms replicate. TheyC. trachomatis is epidemic, the organism may be transmitted from infected then enter the blood and travel to the lungs, the primary target of infec-mother to infant during passage through the birth canal. Data from studies tion, and other organs. Histologic examination of lung tissue shows lym-in North America indicate that 60%–70% of infants exposed to C. tracho- phocytes in the alveolar and interstitial spaces and mucous plugging of thematis during vaginal delivery become infected with the organism, whereas bronchioles. Small hemorrhages and macrophages with intracytoplasmicinfection after cesarean section is uncommon (Jones, 2000). Among inclusions may be seen. The hilar lymph nodes, liver, and spleen may be15–24-year-old women seen in prenatal clinics in participating states in enlarged and may contain foci of necrosis; in fatal cases, the myocardium,2009, the CDC reported a C. trachomatis positivity rate of 7.7% overall, pericardium, meninges, brain, and adrenals may be involved.with a range of 3.6%–20.4%, depending on the state (Centers for DiseaseControl and Prevention, 2009). C. trachomatis is recovered from the con- Clinical Manifestationsjunctiva of infected infants after 1–2 weeks and from the nasopharynx soon After an incubation period of 1–2 weeks, psittacosis may begin abruptlythereafter. The rate of isolation from the conjunctiva falls by 5–6 weeks, with chills and fever, or it may begin more gradually with increasing feverbut C. trachomatis can be recovered from the nasopharynx, conjunctiva, and malaise. Persistent dry, hacking cough, occasionally productive ofrectum, and vagina (usually without producing symptoms) for several blood-streaked mucoid sputum, is prominent. The heart rate is often slowmonths. relative to body temperature, and a diffuse, severe headache is usual. Inclusion conjunctivitis, the most common manifestation of infection Malaise, anorexia, painful myalgias, and arthralgias are common, and awith C. trachomatis in infants, develops in nearly 80% of infants whose macular rash (Horder spots) resembling the rose spots of typhoid feverconjunctival culture or cytologic examination demonstrates the organism may occur. Decreased mentation may develop at the end of the first week(Jones, 2000), and among those with conjunctivitis, approximately 50% of illness, and some may have gastrointestinal complaints. C. psittaci is awill have a nasopharyngeal infection. A mucopurulent discharge appears rare cause of destructive endocarditis; most affected persons have a2–25 days after birth, and the conjunctiva becomes inflamed and edema- history of rheumatic heart disease or congenital valvular abnormalitiestous. Severity ranges from a mild infection with scant discharge to copious (Jones, 1982).mucopurulent discharge with severe swelling and pseudomembraneformation. Approximately 20%–30% of infants who acquire infection with CHLAMYDOPHILA (FORMERLYC. trachomatis at birth develop interstitial pneumonitis. The illness beginsat between 2 weeks and 3 months of age (peak, 3–6 weeks) with nasal CHLAMYDIA PNEUMONIAE)congestion, followed by a distinctive staccato cough with tachypnea and In 1986, a unique chlamydial organism, initially considered to be a strainrales but no fever. Hyperinflation with interstitial or alveolar infiltrates on of C. psittaci, was associated with acute respiratory tract disease in humans.chest radiograph and peripheral eosinophilia are frequently seen. About The organism was named TWAR for the laboratory identifying letters ofone half of patients have or have had conjunctivitis. Symptoms last several the first two isolates: TW-183, isolated in 1965 from the eye of a controlweeks, but inspiratory rales and chest roentgenographic changes may child in a trachoma vaccine trial in Taiwan, and AR-39, recovered the samepersist for months. year from the throat of a student with pharyngitis at the University of 1067
  • 4. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS Washington. Soon after its recognition, data from DNA homology and contain an adequate sample of infected epithelial cells. Purulent discharge electron microscopic studies showed that this unique organism was a sepa- is not an appropriate specimen and should be removed before a sample is rate species, designated as Chlamydia pneumoniae, which has been reclassi- collected with a swab or brush. Of the types of swabs available, Dacron- or fied as Chlamydophila pneumoniae (Campbell, 1987; Chi, 1987; Cox, 1988; rayon-tipped swabs are preferred. Swabs with wooden shafts should be Everett, 1999). avoided because wood is toxic to the organism. Calcium alginate swabs may be toxic to the chlamydias or to the cells that support their growth. Epidemiology Cotton-tipped swabs are acceptable but are occasionally toxic to the chla- The epidemiology of infection with C. pneumoniae is based on data from mydias. Collection of urine for nucleic acid amplification testing should retrospective studies of sera collected during respiratory tract illnesses. follow the recommendations of the manufacturer. About 50% of adults have antibodies to C. pneumoniae. Antibody preva- lence rates are low in children, increase sharply in teenagers, continue to Cell Culture increase until middle age, and remain high into old age; rates are 10%– Cell culture is the reference method for diagnosis of chlamydial infections 25% higher for males. Data from retrospective and prospective serologic and should be performed when the diagnosis is disputed and in cases of studies indicate that disease caused by C. pneumoniae is endemic in the suspected sexual assault or abuse. Cell lines most commonly used are United States and epidemic in Scandinavia and Finland, but does not occur McCoy or buffalo green monkey cells. Both have equivalent sensitivity, with any consistent seasonal periodicity (Grayston, 1989, 1990). C. pneu- but the latter cells are easier to maintain and are more resistant to cytotoxic moniae appears to be a primary human pathogen, transmitted from person substances; they have been associated with more inclusions and larger to person without an avian or animal reservoir. The mechanism and place inclusions (Krech, 1989). Adding cycloheximide (0.5–1.5 μL/mL) to the of transmission, incubation period, and infectiousness of the organism have growth medium enhances sensitivity. Cell monolayers are grown on glass not yet been determined. coverslips in shell vials or 24-well plates, or on the surface of polystyrene 96-well or 48-well culture dishes. To enhance recovery of C. trachomatis, Pathogenesis specimens are sonicated or agitated on a vortex mixer before inoculation The pathogenesis of infection with C. pneumoniae is unknown. Because to release elementary bodies from host cells, and inoculated shell vials or the illness is generally mild and self-limited, autopsy studies are culture dishes are centrifuged. After incubation for 48–72 hours, monolay- unavailable. ers are fixed and stained with fluorescein-conjugated monoclonal antibod- ies. If a 96-well culture system is used, passaging specimens that are Clinical Manifestations negative for C. trachomatis at 48 hours may enhance detection; however, It is estimated that C. pneumoniae is responsible for at least 10% of passaging does not significantly increase detection in shell vials or 24-well community-acquired pneumonias (Grayston, 1990). The pneumonia plates. Although traditionally the “gold standard” for detection of C. tra- usually is mild with a single subsegmental infiltrate, but it may be severe, chomatis, it is now recognized that because of the fastidious nature of the especially in elderly persons and in those with chronic disease. It often organism, sensitivity of cell culture is only in the 50%–75% range,56 begins with pharyngitis and hoarseness, followed by persistent cough. although with the use of monoclonal antibodies in the staining phase, Although pneumonia is the most common syndrome associated with specificity should be 100% (Solomon, 2004; Carder, 2006). C. pneumoniae infection, serologic studies during epidemics among military trainees have shown that only about 10% of infections with C. pneumoniae Nonculture Direct Detection Methods result in pneumonia, suggesting that infection is frequently mild or asymp- Direct Fluorescent Antibody Tests. The DFA test allows direct visu- tomatic and unrecognized. Other manifestations of C. pneumoniae infection alization of C. trachomatis elementary bodies in smears of clinical speci- are bronchitis, pharyngitis, fever of undetermined origin, otitis, influenza- mens. Total processing time is 30–60 minutes. It is the only test that like illness, myocarditis, endocarditis, and possibly atherosclerosis, permits direct assessment of specimen adequacy. Specimens with columnar although the latter is controversial (Campbell, 1998; Maraha, 2004). or metaplastic squamous cells are acceptable, whereas those with few columnar cells, excessive amounts of mucus, or predominance of squamous cells are not. However, interpretation of the smear is subjective, and opera- LABORATORY DIAGNOSIS tor fatigue can be a problem in high-volume situations. Monoclonal anti- bodies are available from several manufacturers. Antibodies directed Chlamydia trachomatis against the species-specific MOMP of C. trachomatis appear to be more Specimens for detection of C. trachomatis are determined by the type of specific and produce more intense fluorescence than those directed against disease suspected (Table 56-2). Screening women at risk for genital C. the chlamydial LPS (Cles, 1988). Occasionally, even the species-specific trachomatis infection (described earlier) has been shown to decrease the antibodies stain bacteria other than C. trachomatis, perhaps because of rate of pelvic inflammatory disease, thus preventing subsequent reproduc- nonspecific immunoglobulin binding or cross-reactivity. Staining organ- tive sequelae (Nelson, 2001). The transport system selected must be isms other than C. trachomatis is especially frequent with rectal specimens; approved for the test method used. Specific collection techniques are therefore for this site, culture is preferred, although some DFA reagents discussed in Chapter 63. Most infections involve mucous membranes; are approved for evaluation of rectal samples. Monoclonal antibody cross- specimens should be collected directly from the involved surface and must reactivity between Chlamydiaceae and Bartonella has also been reported. The sensitivity of the DFA test has varied from 50% to almost 100% compared with culture as the standard, and specificity is ≥95%. Sensitivity depends on the prevalence of infection in the population being evaluated TABLE 56-2 and the number of elementary bodies required for a positive result (Barnes, Specimens for Detection of Chlamydia trachomatis* 1989) and, in general, is greater with lower cutoff values for elementary bodies and in populations with high prevalence of disease. Disease Specimen Enzyme Immunoassays. EIAs detect chlamydial LPS with monoclonal Mucopurulent cervicitis Endocervical swab, urine or polyclonal antibodies labeled with an enzyme that converts a colorless Acute urethral syndrome (women) Urethral swab, urine substrate into a colored product. Both solid-phase systems, which use Acute endometritis Endometrial aspirate plastic or beads coated with the antibody, and membrane systems are com- Acute salpingitis Fallopian tube biopsy mercially available. Total processing time ranges from 15–30 minutes for Nongonococcal urethritis (men) Urethral swab, urine membrane systems to 3–4 hours for solid-phase systems. Advantages of Inclusion conjunctivitis Conjunctival scrapings/swab EIA include the objective interpretation of results and ease of use for Trachoma Conjunctival scrapings/swab batching large numbers of specimens. As with DFA, the sensitivities of EIAs vary (from about 70%–100%) Lymphogranuloma venereum Lymph node aspirate, biopsy of ulcerated lesion, serum compared with culture as the standard and tend to be higher in popula- tions with a high prevalence of disease, such as persons attending a sexu- Pneumonitis (infants) Serum, tracheobronchial aspirate, ally transmitted disease clinic (Barnes, 1989; Mills, 1992; Clarke, 1993; nasopharyngeal swab Ehret, 1993; Kluytmans, 1993; Warren, 1993). The specificity of EIA is *Urine is acceptable for some enzyme-linked immunoassays and for the commercial 95% or higher. Causes of false-positive results include the presence of a nucleic acid amplification tests. bacterial urinary tract infection (Demaio, 1991) or contamination of the 1068
  • 5. specimen with cervical mucus or vaginal secretions. The latter problem it might be selective in high-prevalence populations. Culture confirmationcan be reduced by improving the specimen collection technique (remov- is optimal in theory but requires a second specimen collected during theing cervical mucus and obtaining a true endocervical sample) and by using first visit or during a return visit, and in the case in which the initial screen-blocking antibodies (Mills, 1992). Point-of-care (POC) rapid tests using ing test was a nucleic acid amplification test, culture is less sensitive andan immunoassay format exist for possible use in situations where an imme- may not confirm a true positive. Several confirmation strategies for nucleicdiate result would be very helpful. One such test, the Biostar Chlamydia acid amplification tests have been suggested. Confirmation of a positiveOIA (optical immunoassay) was evaluated by the CDC in an inner city test may be done by performing a second amplification test, using the sameclinic environment, where it demonstrated a sensitivity of 78.6% and a assay or a different assay that targets a different nucleic acid sequence.specificity of 97.2% when compared with nucleic acid amplification Similarly, the original specimen may be used, or a second specimen may(Bandea, 2009). The test allowed immediate treatment of a significant be obtained. Each strategy poses issues that must be addressed by a testingportion (65.9%) of evaluated patients who otherwise would not have been facility if it is determined that a result is to be confirmed. For example, iftreated. a different assay is to be used on the original specimen, it must be con- firmed that the second assay can utilize a specimen collected using theNucleic Acid Hybridization Tests. A commercially available collection kit of the first, and that no inhibition of amplification will occuracridinium-ester–labeled DNA probe complementary to C. trachomatis (Scragg, 2006). Whether the original specimen or a new specimen is used,ribosomal RNA allows direct detection of C. trachomatis in urogenital and attention must be paid to differing sensitivities of different assays, as a lessconjunctival specimens. The test requires a water bath and a luminometer. sensitive assay should not be used to confirm a result obtained with a moreTotal processing time is 2–3 hours. The sensitivity of the probe test com- sensitive assay (Schacter, 2005). The practice of confirming positive resultspared with culture as the reference method varies for both endocervical of nucleic acid amplification tests is not without controversy, and somesamples and urethral swab specimens in men (76%–97%) (Iwen, 1991; experts do not agree with the recommendation of the CDC to do soKluytmans, 1991, 1994; Blanding, 1993; Clarke, 1993; Warren, 1993; (Schachter, 2006).Centers for Disease Control, 2002b). The specificity of the probe test is97% or greater, and it can be improved with a probe competition assay Serologic Tests(Woods, 1996). Serologic tests have little value for diagnosis of chlamydial genital infec- tions for two reasons. First, antibodies to C. trachomatis persist after theNucleic Acid Amplification. Several nucleic acid amplification tests for infection resolves, so a positive serologic test does not necessarily correlatedirect detection of C. trachomatis in endocervical swab specimens, male with active disease. Second, many serologic tests are not specific forurethral swab specimens, and male and female urine samples are com- C. trachomatis because they detect genus-specific antibodies. Exceptionsmercially available. Total time to a result is 2–5 hours, depending on the include diagnosis of LGV and C. trachomatis pneumonitis in infants.test used and the number of samples being processed. The ability of these Because LGV has a long latent period and clinical diagnosis often istests to accommodate high-volume batch testing has facilitated the increase delayed, antibodies are generally present when the acute phase serum is PART 7in the national screening rate for C. trachomatis infection in women aged collected, and a fourfold rise in titer between acute and convalescent phase16–25 in the United States from 25.3% in 2000 to 41.6% in 2007 (Centers serum samples often cannot be documented. Thus, a single or stablefor Disease Control and Prevention, 2009). Three major assay methods complement fixation titer of 1 : 64 or greater supports a presumptive diag-are currently being utilized in the United States and in Europe to detect nosis of LGV. For diagnosis of C. trachomatis pneumonitis in infants,C. trachomatis in cervical swabs and urine from women and in urethral detection of IgM antibodies by microimmunofluorescence (MIF) may beswabs and urine from men. Two of these methods, the polymerase chain useful. A single IgM titer of >1 : 32 when tested by MIF supports a diag-reaction (PCR) (Roche Diagnostics Corp., Indianapolis, and Abbott Labo- nosis of chlamydial pneumonia. IgG is not useful in neonates because ofratories, Abbott Park, Ill.) and the strand displacement assay (SDA) (Becton circulating maternal antibody.Dickinson Diagnostic Systems, Sparks, Md.) utilize a DNA target, and thethird, transcription-mediated amplification (TMA) (Gen-Probe Inc., San Chlamydophila psittaciDiego) utilizes an RNA target. Data from several studies comparing The CDC has established case definitions for C. psittaci infections, whichnucleic acid amplification and cell culture indicate that the amplification are described as laboratory confirmed if (1) C. psittaci is cultured fromtests are highly specific and more sensitive than culture (Goessens, 1997; respiratory material, or (2) antibody titers against C. psittaci increase four-Carroll, 1998; Ferrero, 1998; Mahony, 1998; Puolakkainen, 1998; Toye, fold or greater when tested by complement fixation or MIF at least 2 weeks1998; Wylie, 1998; Vincelette, 1999; van der Pol, 2001; Koumans, 2003; apart, or (3) a single IgM titer of >1 : 16 when tested by MIF is presentBoyadzhyan, 2004; Gaydos, 2004). TMA has demonstrated higher sensi- after the onset of symptoms (Centers for Disease Control and Prevention,tivity than the other methods, possibly owing to the higher RNA target 1998). C. psittaci can be grown in cell culture, but this is recommendedlevels relative to DNA target levels and the lower susceptibility to inhibi- only for specially equipped laboratories with experienced personnel,tors seen in urine samples, possibly due to a target capture portion of the because the organism is especially virulent and has been associated withassay that precedes amplification (Schacter, 2005; Chernesky, 2006; Lowe, laboratory-acquired infection. Infection with C. psittaci is usually diagnosed2006; Levett, 2008). serologically. Antibodies usually are detected by the end of the second In 2006, an interesting set of events occurred in Sweden that demon- week of illness, but early antibiotic therapy can delay their appearance forstrated the importance of target selection in nucleic acid amplification, in several weeks.that a new variant of C. trachomatis that contained a 377 base pair deletionin the target utilized in the PCR was discovered. The appearance of this Chlamydophila pneumoniaevariant resulted in a high proportion of infected patients escaping detec- Diagnosis of C. pneumoniae infection is based predominantly on serologiction (an estimated 8000 cases) by two systems that utilized the PCR tests (Grayston, 1990; Kumar, 2007). The MIF test with the TWARmethod: the Abbott m2000 and the Roche Cobas Amplicor/TaqMan 48 antigen is specific for C. pneumoniae and is the only serologic test consid-(Herrmann, 2008; Møller, 2008). TMA and SDA methods detected the ered acceptable for use in diagnosis by the CDC and the Infectious Diseasevariant, as amplification targets were different. The new variant spread Society of America (IDSA) (Kumar, 2007). IgM antibodies appear aboutrapidly in Sweden, and by 2007 accounted for up to 65% of cases in which 2–3 weeks after the onset of primary illness, usually decline over the nextthese two platforms were being used (Herrmann, 2008b). Studies demon- 2–6 months to a level that cannot be detected, and may not reappear withstrated that the new variant had no other biological advantage to aid in its reinfection. IgG antibodies are detected 6–8 weeks after onset of therapid spread relative to other strains, other than its ability to escape detec- primary illness, persist for life, and may rise 1–2 weeks following reinfec-tion by the testing systems in use at the time (Unemo, 2010). Affected tion. Serologic test results consistent with acute infection include a four-manufacturers have implemented new assays that detect dual targets, such fold or greater rise in IgG titer between acute and convalescent phasethat the variant is detected (Møller, 2010). serum samples, or an IgM titer of 1 : 16 or greater. The use of single IgG titers is discouraged. Despite prevalent use of the MIF test, it has beenVerification of Nonculture Tests shown to be insensitive, especially in children, and cross-reactions withThe CDC has recommended that positive nonculture test (DFA, EIA, Mycoplasma, Bartonella, and Yersinia species may occur. C. pneumoniae canprobe, nucleic acid amplification) results should be verified with a supple- be isolated in cell culture, but it is more difficult to grow than C. trachomatismental test if a false-positive result is likely to have adverse medical, social, (Roblin, 1992). Many “in-house” nucleic acid amplification assays foror psychological consequences (Centers for Disease Control, 1993, 2002b). C. pneumoniae have been published, but very few have been validatedIn low-prevalence populations, verification should probably be routine, but clinically (Kumar, 2007). 1069
  • 6. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS A newly recognized transitional group contains Rickettsia akari, Rickettsia TREATMENT australis, and Rickettsia felis. R. akari and R. australis were traditionally Tetracyclines have been the treatment of choice for infection with chla- considered to be relatively distant members of the spotted fever group, mydia. For genital infections due to C. trachomatis, recommended regimens with which they share LPS antigens. include azithromycin (1g orally, 1 dose) or doxycycline (100mg orally twice a day for 7 days); other effective agents include erythromycin, ofloxacin, Rocky Mountain Spotted Fever or levofloxacin (Centers for Disease Control, 2006). LGV requires the The most severe of all the rickettsioses, Rocky Mountain spotted fever, same daily dosage of doxycycline or erythromycin as genital infections, but has a substantial case fatality rate, 5%, even among previously healthy, for a period of 3 weeks. Ocular infections with C. trachomatis require sys- immunocompetent children and young adults (Dalton, 1995a; Paddock, temic treatment with doxycycline or azithromycin for adults, and erythro- 1999). R. rickettsii normally resides in nature in ticks: Dermacentor variabilis, mycin for newborns; topical therapy suppresses symptoms but does not the American dog tick, in the eastern two thirds of the United States and eradicate the organism. Macrolides (azithromycin and erythromycin) are California; Dermacentor andersoni, the Rocky Mountain wood tick, in the acceptable alternative agents for doxycycline in infections caused by western United States; Rhipicephalus sanguineus, the brown dog tick, in C. pneumoniae. For C. psittaci, the treatment of choice is tetracycline hydro- Mexico, Brazil, and Arizona; and Amblyomma cajennense and A. aureolatum chloride or doxycycline for 3 weeks. Erythromycin is an alternative but in South America. These ticks maintain R. rickettsii as they moult from may be less effective in more severe cases. stage to stage (larva, nymph, and adult) and transovarially from generation to generation. Fewer than 1 per 1000 ticks carries virulent R. rickettsii, which is pathogenic for ticks (Niebylski, 1999). New lines of ticks become RICKETTSIAL INFECTIONS infected by feeding on rickettsemic rodents, replenishing the population Rickettsia is a concept that developed historically as the molecular and of organisms transovarially maintained in ticks (Gage, 1990). physical nature of viruses was defined (Weiss, 1988). In contrast with Infections occur when and where humans encounter R. rickettsii– human viral agents, which also require eukaryotic host cells for their infected ticks (Helmick, 1984). Although Rocky Mountain spotted fever intracellular replication, rickettsiae have a gram-negative bacterial cell has been documented in recent years in nearly every state except Hawaii, wall, and their growth is inhibited by particular antibiotics. Rickettsiae are Alaska, and Vermont, the highest incidence is in the south Atlantic states further differentiated from other obligately intracellular bacteria by their from Maryland to Georgia and the south central states of Oklahoma, Mis- ecology and frequent transmission by arthropod vectors. The traditional souri, Arkansas, and Tennessee. Most cases occur in late spring and taxonomic scheme of rickettsiae based on such phenotypic characteristics summer, but particularly in the southern latitudes, a few cases may occur as intracellular growth and arthropod vector transmission has undergone even in winter. The highest incidence is seen in children, adults of retire- substantial modification in light of contemporary gene sequence analyses. ment age, and others exposed to ticks during outdoor activities. Fatality/ Genera that contain rickettsiae pathogenic for humans are Rickettsia, Ori- case ratios are higher for persons older than 30 years. Fulminant entia, Ehrlichia, Anaplasma, Neorickettsia, Coxiella, and Bartonella (Dumler, Rocky Mountain spotted fever (death by the fifth day of illness) occurs in56 2001; Yu, 2003). Despite their historical association with rickettsiology and association with moderate hemolysis, for example, in African American arthropod transmission, Bartonella organisms are cultivable in cell-free males with glucose-6-phosphate dehydrogenase (G6PD) deficiency medium and do not belong in the order Rickettsiales (Brenner, 1993), (Walker, 1983). which includes the genera Rickettsia, Orientia, Ehrlichia, Anaplasma, and Rickettsiae are injected via the infected tick’s salivary gland secretions Neorickettsia, which are more closely related to one another than to Coxi- into the patient’s dermis after 6–10 hours of tick feeding and spread hema- ella. Grouped by genus, the following diseases are presented in this chapter: togenously throughout the body. The vascular endothelium is the target Rickettsia—Rocky Mountain spotted fever, boutonneuse fever, African tick of intracellular infection, with some invasion into adjacent vascular smooth bite fever, rickettsialpox, and murine typhus; Orientia—scrub typhus; muscle cells. Infected endothelium is injured by reactive oxygen species– Ehrlichia—human monocytotropic ehrlichiosis caused by Ehrlichia chaffeen- induced damage to cell membranes (Silverman, 1992, 1997). Damage to sis and human infection with Ehrlichia ewingii; Anaplasma—human granu- the endothelium results in increased vascular permeability, edema, hypo- locytotropic anaplasmosis; Coxiella—Q fever; and Bartonella—cat scratch volemia, and hypotension. Life-threatening consequences of vascular disease, bacillary angiomatosis and peliosis, trench fever, and South Ameri- injury in the central nervous system (CNS) and lung are rickettsial menin- can bartonellosis. The diseases of each genus comprise cohesive clinical goencephalitis and noncardiogenic pulmonary edema. Early in the course, and pathologic groupings, and overall the rickettsial diseases pose a similar lesions show endothelial rickettsiae without thrombi or a cellular response. set of diagnostic challenges, with similar technical approaches to their Late in the course, the characteristic lymphohistiocytic perivascular infil- solution. trate appears as interstitial pneumonia, interstitial myocarditis, perivascu- lar glial nodules of the brain, and similar vascular lesions in the dermis, gastrointestinal tract, liver, skeletal muscles, and kidneys. Severe injury INFECTIONS CAUSED BY ORGANISMS may be accompanied by focal hemorrhages but seldom by microinfarcts, OF THE GENUS RICKETTSIA except in the white matter of the brain. Clinical illness usually begins with fever, headache, and myalgia 2–14 Structure and Function days after a tick bite (Kaplowitz, 1981). Nausea, vomiting, abdominal pain Spotted fever, transitional, and typhus group rickettsiae are genetically and tenderness, and diarrhea occur more frequently in the first 3 days of closely related bacteria that have a thin (0.3–0.5 × 1–2 μm) bacillary mor- illness. The rash, which usually appears between days 3 and 5, typically phology and a gram-negative cell wall containing LPS with antigenic begins as macules around the wrists and ankles and later on the arms, legs, components that distinguish the spotted fever and typhus groups. All and trunk. The lesions become maculopapular, and in half of cases, a Rickettsia species reside free in the cytosol of the host cell and divide by central petechia appears in many of the maculopapules. Characteristic binary fission. Rickettsia attach to the host cell via a protein adhesin, enter involvement of the palms and soles occurs in half of cases as a late mani- by induced phagocytosis, and escape from the phagosome (Li, 1998; Uchi- festation. Renal failure is a feature of severe illness. CNS involvement is yama, 1999; Martinez, 2004; Martinez, 2005). These functions can occur ominous; seizures and coma occur in 8%–10% of cases overall, often within minutes and are associated with phospholipase activity of rickettsial preceding a fatal outcome. Thrombocytopenia occurs in half of cases, but origin (Silverman, 1992; Whitworth, 2005). Spotted fever group rickett- disseminated intravascular coagulation is rare (Elghetany, 1999). siae are propelled within cells and during release from the cell by stimulat- ing polymerization of host cell F-actin at one pole (Heinzen, 1993; Kleba, 2010). Rickettsia that manifest this activity (e.g., Rickettsia rickettsii) escape African Tick Bite Fever, Boutonneuse Fever, earlier from host cells and spread more quickly to other cells than those and Other Spotted Fevers lacking this activity (e.g., Rickettsia prowazekii), which divide intracellularly R. conorii has been isolated in southern Europe; northern, eastern, and to massive numbers before the host cell bursts and the organisms are southern Africa; Israel; Turkey; India; Pakistan; Russia; Georgia; and the released. According to the molecular phylogeny, Rickettsia species that are Ukraine. The ecology of R. conorii and the epidemiology of boutonneuse pathogenic for humans have evolved into three genogroups (Table 56-3) fever are closely tied to ticks, especially R. sanguineus, which maintain the (Roux, 1995, 1997; Stothard, 1995). The typhus group includes R. prowa- rickettsiae transovarially and transmit the infection to humans while zekii and Rickettsia typhi. The core spotted fever group contains R. rickettsii, feeding (Walker, 1991). Imported cases are diagnosed in travelers return- Rickettsia conorii, Rickettsia japonica, Rickettsia africae, Rickettsia parkeri, Rick- ing to the United States and northern Europe from the Mediterranean ettsia honei, Rickettsia sibirica, Rickettsia aeschlimannii, and Rickettsia slovaca. basin. The fatality rate among hospitalized patients is 1.4%–5.6%, 1070
  • 7. TABLE 56-3Rickettsia, Orientia, Ehrlichia, Anaplasma, Neorickettsia, Coxiella, and Bartonella InfectionsEtiologic agent Disease Geographic distribution TransmissionSpotted FeversR. rickettsii Rocky Mountain spotted fever North, Central, and South America Tick biteR. conorii Boutonneuse fever Southern Europe, Africa, Russia, Tick bite Georgia, Middle East, Indian subcontinentR. africae African tick bite fever Southern and eastern Africa, Caribbean Tick biteR. parkeri Maculatum disease North and South America Tick biteR. sibirica North Asian tick typhus and Russia, China, Mongolia, Pakistan, Tick bite lymphangitis-associated rickettsioses Europe, AfricaR. japonica Japanese spotted fever Japan, Korea, Thailand Tick biteR. honei Flinders Island spotted fever Australia, southeastern Asia Tick biteR. slovaca Tick-borne lymphadenopathy Europe Tick biteTyphus FeversR. prowazekii Epidemic typhus Potentially worldwide; in recent Feces of human body louse decades in Africa, South America, Central America, Mexico, AsiaR. prowazekii Brill-Zinsser disease Worldwide; wherever persons with past Recrudescence of latent epidemic typhus now reside infectionR. prowazekii Flying squirrel typhus United States Presumably feces of flea or louse of flying squirrelR. typhi Murine typhus Worldwide in tropics and subtropics Flea fecesTransitional GroupRickettsial FeversR. akari Rickettsialpox United States, Ukraine, Croatia, Korea, Mite bite Turkey, Mexico PART 7R. australis Queensland tick typhus Eastern Australia Tick biteR. felis Flea-borne spotted fever Worldwide Presumably flea bite or fecesScrub TyphusOrientia tsutsugamushi Scrub typhus Southeastern Asia, Japan, China, Sri Chigger bite Lanka, India, Asiatic Russia, Indonesia, Indian Ocean and Western Pacific Islands, Northern AustraliaEhrlichiosesE. chaffeensis Human monocytotropic ehrlichiosis United States, Africa, Asia Tick biteE. ewingii Ehrlichiosis ewingii United States, Africa Tick biteAnaplasma phagocytophilum Human granulocytotropic anaplasmosis United States, Eurasia Tick biteNeorickettsia sennetsu Sennetsu rickettsiosis Asia Apparently ingestion of fish parasitized with trematodes carrying neorickettsiaCoxiellosisC. burnetii Q fever Worldwide Inhalation of aerosols from infected animals, possibly ingestion of animal productsBartonellosesB. bacilliformis Oroya fever, verruga peruana Western South America Sandfly biteB. henselae Cat scratch disease, bacillary Worldwide Kitten scratch or bite angiomatosis and peliosis, endocarditisB. clarridgeiae Cat scratch–like disease Probably worldwide Presumed cat scratch or biteB. quintana Trench fever, endocarditis Worldwide Feces of Pediculus louseparticularly in patients with underlying conditions such as diabetes and and infection with R. honei has been documented in Australia and Thailand.alcoholism (de Sousa, 2008). A milder disease caused by R. africae occurs After an average incubation period of 7 days, these illnesses begin withwith high frequency in travelers returning from southern Africa (McQuis- fever, headache, and myalgias. Frequently, an eschar can be discovered byton, 2004). The clinical illness resembles that recently associated in the careful examination of the skin at this time. The pathology of these spottedAmericas with R. parkeri, which is essentially conspecific with R. africae fevers is well described in the tache noire or eschar at the site of tick bite(Paddock, 2004, 2008). Tick bite eschars are often multiple, regional inoculation of rickettsiae (Walker, 1988a). Endothelial infection and injurylymphadenopathy is observed frequently, and rash is typically sparse, by R. conorii in the eschar result in dermal and epidermal necrosis andsometimes vesicular, and often absent. R. sibirica has been isolated in perivascular edema.Russia, China, Mongolia, and Pakistan, and a distinct strain mongoliti- Host defenses that effect killing of intracellular rickettsiae includemoniae isolated in Asia, Europe, and Africa has been associated in half of nitric oxide, reactive oxygen species, and tryptophan limitation induced bycases with lymphangitis extending from the eschar. R. japonica has been cytokines secreted by T lymphocytes and macrophages, which infiltratedocumented in Japan, and infection with R. japonica occurs also in Korea around the infected dermal blood vessels and target cell apoptosis trig-and Thailand. Human infections with R. australis occur only in Australia, gered by cytotoxic CD8+ T lymphocytes (Herrero-Herrero, 1987; Walker, 1071
  • 8. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS 2001; Valbuena, 2002). Activation of endothelial cells by cytokines, includ- 1989). The most serious consequences include meningoencephalomyelitis ing γ-interferon and tumor necrosis factor-α, results in intracellular and diffuse alveolar injury. rickettsicidal activity, and ultimate clearance is mediated by cytotoxic T lymphocytes. Disseminated endothelial infection results in maculopapu- Rickettsiae as Agents of Bioterrorism lar rash, meningoencephalitis, and vascular lesions in the lungs, kidneys, R. prowazekii and R. rickettsii are select agents, possession of which is gastrointestinal tract, and heart (Walker, 1985). Multifocal hepatocellular restricted by law to registered scientists in approved institutions where necrosis and granuloma-like lesions correlate with moderately increased rigorous security and safety regulations are applied to the laboratories. concentrations of hepatic transaminases (Walker, 1986). These organisms exist in nature, can be recovered and propagated, and are infectious via a stable aerosol, with infectivity of as little as a single Rickettsialpox bacterium. R. akari is maintained in nature by transovarial transmission in the gamasid Case fatality rates of 15%–25% in previously healthy persons would mite, Liponyssoides sanguineus, an ectoparasite of the domestic mouse, Mus occur without prompt diagnosis and treatment. The potential for geneti- musculus. R. akari has been detected only in the United States, Croatia, the cally engineered resistance to the effective antibiotics, tetracycline and Ukraine, Turkey, Mexico, and Korea, perhaps more an indication of the chloramphenicol, would render these cases of typhus and Rocky Mountain paucity of rickettsial investigations than the actual distribution of this spotted fever untreatable (Walker, 2003). Although the case fatality rates rickettsial species. would be lower, bioterrorist-dispersed R. typhi or R. conorii could create A papule develops during the approximately 10-day incubation period terror and overwhelm the medical and public health systems. at the site of mite bite and progresses to become a 1–2.5cm eschar. Illness begins with chills, fever, malaise, severe headache, and myalgia. Rash, Laboratory Diagnosis which appears 2–6 days later, is initially maculopapular, later papular, and Unlike most infectious diseases for which precise diagnosis is sought in classic cases, pustular and/or vesicular. Some patients also suffer nausea, during the acute phase of illness, when critical therapeutic decisions are vomiting, pharyngitis, photophobia, splenomegaly, and nuchal rigidity. made, rickettsial diseases are usually diagnosed acutely purely on the basis Histopathologic examination of the eschar reveals coagulative necrosis of clinicoepidemiologic suspicion, and are treated empirically on a pre- of the epidermis, underlying vascular injury, and a perivascular lympho- sumptive basis (Kaplowitz, 1981). Serologic diagnosis, which is often mis- histiocytic infiltrate in which macrophages appear to be the main target takenly sought early in the course of illness, provides the majority of cell of infection (Brettman, 1981; Kass, 1994; Walker, 1999b). Regional laboratory-confirmed diagnoses by demonstration of a fourfold or greater lymphadenopathy and cutaneous rash presumably reflect lymphogenous rise in titer only during convalescence. Even with the most sensitive sero- and hematogenous spread, respectively. logic methods, less than 20% of patients have detectable specific antibodies to rickettsiae when presenting to the physician for medical attention. Flea-borne Spotted Fever Other approaches to diagnosis at the time of presentation include immu- A widely dispersed organism, R. felis is maintained transovarially in cat fleas nohistologic demonstration of rickettsiae in cutaneous lesions, immuno-56 (Ctenocephalides felis) with apparent involvement of opossums in a zoonotic cytologic identification of rickettsiae in circulating detached endothelial cycle. Human infections have been documented in North America, cells, detection of rickettsial DNA in blood and tissue specimens by PCR Europe, Africa, and Asia (Schriefer, 1994a; Zavala-Velazquez, 2000; (Schriefer, 1994a; Sexton, 1994; Williams, 1994; Furuya, 1995), and culti- Raoult, 2001; Parola, 2003). vation of rickettsiae from blood or tissue specimens; however, these tests are not available in most clinical laboratories. Murine Typhus and Louse-borne Typhus Rickettsiae were originally demonstrated in tissues of patients with Endemic flea-borne R. typhi infection, murine typhus, is presently the most Rocky Mountain spotted fever and epidemic louse-borne typhus by important typhus group infection in the United States and causes extensive Wolbach using Giemsa stain during and shortly after World War I. This morbidity throughout the warm regions of the world (Azad, 1990). His- method, essentially a lost art, requires careful attention to details of fixation torically, epidemic louse-borne R. prowazekii infections have had a major and staining of rickettsiae, and is not performed successfully in this manner impact on the outcome of military campaigns, as well as scourging general in contemporary histology laboratories. A modified Brown-Hopps method populations disrupted by war, famine, and natural disasters (Zinsser, 1935; stains a small fraction of organisms, which appear as thin bacilli within Patterson, 1993). R. prowazekii continues to cause disease in some poverty- endothelial cells. A more sensitive and specific approach to visualization stricken areas of the world and reappears in situations such as the civil war of rickettsiae in tissue section is immunohistology—immunofluorescence in Burundi, the extreme poverty of indigenous populations of the Andes, or immunoenzyme staining—using antibodies specific for the spotted fever and other unsettled social and economic conditions. Recrudescence of or typhus group (Kaplowitz, 1983; Walker, 1989, 1997b, 1999b; Dumler, latent R. prowazekii infections can occur years after the primary infection 1990). Staining of skin biopsies from patients with Rocky Mountain in immigrants from typhus-afflicted areas. Endemic transmission of spotted fever by immunohistochemistry has a sensitivity of 70% and a R. prowazekii from a natural infectious cycle of flying squirrels and their specificity of 100%. Patients with boutonneuse fever, African tick bite ectoparasites occurs in the United States (McDade, 1980; Reynolds, 2003). fever, murine typhus, and rickettsialpox have also been diagnosed by Murine typhus occurs particularly in tropical and subtropical coastal immunohistologic detection of rickettsiae in rash and eschar lesions. A areas, where Rattus rattus, Rattus norvegicus, and the Oriental rat flea monoclonal antibody to a spotted fever group–specific epitope on the cell abound (Azad, 1990). The fleas imbibe rickettsiae in the blood of infected wall LPS demonstrates R. rickettsii, R. parkeri, R. conorii, R. akari, R. japon- rats and maintain the infection for their normal life span. Transovarian ica, R. australis, R. africae, R. honei, and R. sibirica in formalin-fixed, paraffin- transmission occurs only at low levels; thus, horizontal transmission to embedded tissues; a typhus group LPS-specific monoclonal antibody is other rats is a key factor in maintenance of R. typhi in nature. Other similarly useful for detecting R. typhi and R. prowazekii (Walker, 1997b). mammal-arthropod cycles maintain the rickettsiae and result in transmis- Currently, reagents for diagnostic immunohistology of rickettsioses are not sion of infection to humans (e.g., the cat flea, C. felis, and the opossum in commercially available, but it is feasible that kits could be developed for Texas and California) (Schriefer, 1994b). rickettsial group–specific diagnosis using antibodies produced in research Humans are thought to become infected by intradermal inoculation of laboratories. infected flea feces into skin excoriated by scratching. However, inhalation A unique diagnostic approach is the immunocytologic demonstration of a rickettsial aerosol from dried infected flea feces or inoculation by flea of R. conorii in detached, circulating endothelial cells captured from patient bite may account for transmission in some cases. After an incubation period blood samples by immunomagnetic beads coated with a monoclonal anti- of 1–2 weeks, illness begins with fever accompanied in some cases by severe body to a surface antigen of human endothelial cells (Drancourt, 1992; La headache, chills, myalgia, and nausea. A macular or maculopapular rash, Scola, 1996a). In boutonneuse fever patients, this method has a sensitivity most prominent on the trunk, is visualized on day 5 or 6 in 80% of patients of 58% for examination of a single blood sample and may be used in with fair skin and in 20% with darkly pigmented skin. A small proportion patients before the onset of rash, which must be present for selection of of patients have cough and pulmonary infiltrates. Severely ill patients may the site of skin biopsy for immunohistologic diagnosis. also suffer coma, seizures, and other neurologic signs. Approximately 10% PCR has been applied successfully to the diagnostic detection of of hospitalized patients require admission to the intensive care unit, and R. rickettsii, R. conorii, R. japonica, R. africae, R. parkeri, R. felis, R. akari, 1%–2% of murine typhus patients die (Dumler, 1991). R. sibirica, R. slovaca, R. aeschlimannii, R. typhi, and R. prowazekii from Pathologic lesions of murine typhus include endothelial swelling and clinical samples, including biopsy of eschar or rash, peripheral blood, perivascular lymphohistiocytic infiltrates involving the blood vessels in the buffy coat, plasma, necropsy tissue, and arthropod vectors removed from dermis, CNS, lungs, heart, gastrointestinal tract, and kidneys (Walker, patients. Target genes include the 17-kDa lipoprotein gene, gltA, rrs, 1072
  • 9. groEL, ompA, and ompB. This approach may fail to detect rickettsial nucleic the cutaneous chigger inoculation sites and organs to which rickett-acids early in the course or after development of immunity or effective siae have disseminated—the brain, lung, heart, gastrointestinal tract, andantimicrobial treatment (Tzianabos, 1989; Schriefer, 1994a; Sexton, 1994; kidney.Furuya, 1995; Roux, 1999; Leitner, 2002; Walker, 2003; Fournier, 2004; After incubation for 6–21 days, illness begins with fever, headache, and,Ndip, 2004; Stenos, 2005; Kidd, 2008; Nascimento, 2009; Prakash, 2009). in some patients, myalgia, cough, and gastrointestinal symptoms (Watt, Isolation of rickettsiae is achieved frequently in antibiotic-free, 2006). An eschar develops in half of Westerners, usually before the onsetcentrifugation-enhanced shell vial cell culture in reference and research of fever, but less often in indigenous patients. Likewise, a macular orlaboratories with biosafety level 3 containment and specialized expertise. maculopapular rash occurs in half of Westerners with primary infection The “gold standard” serologic test for rickettsioses is the indirect 2–9 days after the onset of illness. Severely ill patients may develop hypo-immunofluorescent antibody (IFA) assay (Kaplan, 1986). The indirect tension, pneumonitis, meningoencephalitis, acute renal failure, and hem-immunoperoxidase antibody test yields similar results. For spotted fever orrhagic phenomena. Unless treated with appropriate antimicrobialand typhus-group rickettsial infections in the United States, IFA titers of medications, 7% of cases are fatal. Greater severity is associated with1 : 64 or greater are considered to be diagnostic in a compatible clinicoepi- greater bacterial loads (Sonthayanon, 2009). Scrub typhus may occur indemiologic situation. In countries with a high prevalence of persons with trekkers and other travelers exposed to chiggers in endemic areas. For theantibodies to these rickettsiae, due hypothetically to stimulation by non- diagnosis of scrub typhus in an endemic region, the cutoff titer should bepathogenic rickettsiae or subclinical or undiagnosed infection, higher titers determined for the particular population; for one region, a titer of 1 : 400are required to establish the diagnosis. In any event, a fourfold rise in IFA or greater by IFA is 96% specific and 48% sensitive, and a fourfold rise inantibody titer to a titer of at least 1 : 64, but usually 1 : 256 or higher, is titer is the preferred serologic criterion for diagnosis (Blacksell, 2007).diagnostic. The sensitivity of the IFA for Rocky Mountain spotted fever is Indirect immunoperoxidase is a similar method that does not require a94%–100%, and the specificity is 100%. With a cutoff titer for IgG of fluorescent microscope. Proteus mirabilis strain OX-K agglutination is1 : 128 and for IgM of 1 : 32, the indirect immunoperoxidase test yields more readily available but insensitive. Serologic assays using a recombinantsimilar results and has the advantage of requiring only a light microscope 56-kDa antigen representing the major immunodominant surface protein,instead of an ultraviolet microscope. including a dipstick test, a rapid lateral flow assay, and an IgM capture Commercially available serologic tests include indirect immunofluores- enzyme immunoassay, yield excellent results. (Ching, 2001; Coleman,cence, latex agglutination, and standard solid-phase enzyme immunoassay 2002; Jang, 2003; Jiang, 2003).(Kelly, 1995). Latex agglutination and solid-phase enzyme immunoassays PCR has been applied to the diagnosis of scrub typhus for more thanprovide diagnostically useful information and require less expensive equip- a decade (Murai, 1992; Furuya, 1993; Kawamori, 1993; Sugita, 1993) andment to perform, but generally are not considered as reliable as the IFA. has been demonstrated to be effective in practice, including on escharThe greatly increased reliance of reference laboratories on EIAs has specimens (Manosroi, 2003; Saisongkorh, 2004; Kim, 2006; Paris 2008,occurred in parallel with anomalous changes in public health reports of 2009). Real-time PCR offers the opportunity for a highly sensitive, specificRocky Mountain spotted fever. It has been suggested that a substantial diagnosis with prompt turnaround time (Jiang, 2004). PART 7portion of the tick-exposed population has standing titers of antibodies Treatment with a tetracycline drug such as doxycycline or with chlor-stimulated by spotted fever group rickettsiae of low pathogenicity (Graf, amphenicol is effective, except among some cases in northern Thailand,2008; Walker, 2008). The Weil-Felix tests, which measure agglutination where rifamycin and azithromycin are alternatives (Strickman, 1995; Watt,of Proteus vulgaris strains OX-19 and OX-2 (Kaplan, 1986), are insensitive 1996, 2000; Kim, 2004; Liu, 2006).and nonspecific and should not be used, except in developing countries inwhich no other method can be performed. Serology is seldom useful inassisting therapeutic decisions because antibodies appear later in the INFECTIONS CAUSED BY ORGANISMS OFcourse. THE GENERA EHRLICHIA AND ANAPLASMATreatment Structure and FunctionSpotted fever and typhus group rickettsioses are treated effectively with The family Anaplasmataceae consists of four genera—Ehrlichia, Anaplasma,doxycycline, tetracycline, or chloramphenicol (Raoult, 1991). Fluoroqui- Neorickettsia, and Wolbachia. Ehrlichiae and anaplasmae are small (0.5 μm),nolones, azithromycin, and clarithromycin are active against some rickett- tick-borne, obligately intracellular, gram-negative coccobacilli that residesiae in vitro. Ciprofloxacin, ofloxacin, and perfloxacin have been used in a cytoplasmic vacuole of white blood cells (Yu, 2003). This intravacuolarsuccessfully to treat boutonneuse fever, and azithromycin and clarithromy- microcolony of bacteria stained by the Wright-Giemsa method resemblescin have been used to treat mild boutonneuse fever in children, but these a mulberry and thus is called a morula (Latin for “mulberry”). Neorickettsia,agents have not been evaluated and are not recommended for treatment similar small obligately intracellular bacteria, reside in trematode parasitesof Rocky Mountain spotted fever. in aquatic snails, insects, bats, and fish, and are transmitted by ingestion of a parasitized host (e.g., Neorickettsia helminthoeca in trematode-parasitized salmon eaten by dogs in the Pacific Northwest). Wolbachia reside in arthro-SCRUB TYPHUS CAUSED BY pods and filarial worms (e.g., Onchocerca volvulus), in which they play a role in the pathogenesis of the human illness.ORIENTIA TSUTSUGAMUSHI Long known and studied as agents of veterinary disease, Ehrlichia andThe gram-negative cell wall of Orientia (formerly Rickettsia) tsutsugamushi Anaplasma have recently emerged as human pathogens. The reasons fordiffers from that of spotted fever and typhus group rickettsiae; it has an this are primarily their recent discovery in humans, their rapid character-ultrastructurally thicker outer leaflet and a thinner inner leaflet of the outer ization with contemporary molecular tools, and increasing populations andenvelope and different major proteins, and it lacks LPS (Tamura, 1995). geographic distributions of particular ticks that depend on deer as a host.Scrub typhus rickettsiae grow in the cytoplasm of the host cell and are The well-documented human pathogens in the United States arereleased via a process involving pinching off of a host cell membrane– E. chaffeensis, E. ewingii, and Anaplasma phagocytophilum. Neorickettsiabound rickettsia. O. tsutsugamushi is transovarially maintained in mites of sennetsu is the agent of a disease in Asia resembling infectiousthe genus Leptotrombidium (Traub, 1978). Infected ova hatch into larvae— mononucleosis.the only stage that feeds on an animal host. Rats become infected afterrickettsia-containing larvae (chiggers) feed on the rats’ tissue fluids, but Human Monocytotropic Ehrlichiosisfeeding mite larvae that acquire rickettsiae do not pass the infection to E. chaffeensis is transmitted by ticks, primarily Amblyomma americanum, thetheir offspring. Thus, humans and rats are only accidental, nonessential, Lone Star tick, but also D. variabilis and Ixodes pacificus (Anderson, 1992a;dead-end hosts of scrub typhus rickettsiae. Scrub typhus occurs in coun- Ewing, 1995; Kramer, 1999). Cases are predominantly rural and seasonaltries within the geographic area formed by Japan, Russia, and Korea in the (68% occur from May to July) (Fishbein, 1994; Olano, 2003a). Deer serveNorth, Australia and Indonesia in the South, Pakistan in the West, and the as a documented reservoir, and infected dogs and coyotes are potentialPhilippines and Micronesia in the East. Infection is acquired in areas of reservoir hosts. Ticks become infected when feeding as larvae or nymphs,dense vegetation where abundant rat populations harbor large populations carry the ehrlichiae as they moult from stage to stage, and transmit theof chiggers. infection during a subsequent blood meal. Human monocytotropic O. tsutsugamushi infects endothelial cells more extensively than macro- ehrlichiosis has been reported in 47 states; most cases have occurred withinphages (Moron, 2001). The basic pathologic lesion is vascular injury the range of A. americanum in the third of the United States south of awith perivascular lymphohistiocytic inflammation, which is present in line from New Jersey to Kansas. The number of reported cases is 1073
  • 10. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS particularly high in Oklahoma, Missouri, Arkansas, Tennessee, North elevated hepatic enzymes, and severely ill patients may have septic shock– Carolina, and Maryland. like illness with multiorgan involvement. Since the first case of human ehrlichiosis was reported in the United States in 1987, prospective studies have documented an incidence of Laboratory Diagnosis laboratory-confirmed E. chaffeensis infection that exceeds that of Rocky Isolation of ehrlichiae and anaplasmae from human blood in antibiotic-free Mountain spotted fever and is two orders of magnitude greater than sug- cell culture has been accomplished more often for A. phagocytophilum (in gested by passive reporting (Olano 2003b; Demma, 2005). Human ehrlichi- HL-60 cells) than for E. chaffeensis (in DH-82 cells), and only once for E. osis may represent the most serious tick-transmitted infection in the United canis (in an asymptomatic person), and has yet to be reported for E. ewingii States. Fatalities have occurred in approximately 3% of cases—a rate that (Dawson, 1991; Edelman, 1996; Goodman, 1996; Perez, 1996; Childs, would be much higher without effective antibiotic treatment in many 1999). Amplification of ehrlichial DNA by PCR using species-specific patients (Fichtenbaum, 1993; Fishbein, 1994). The severity is reflected in primers is an efficient diagnostic tool for all the human ehrlichioses the admission of 41%–62% of patients to a hospital (Fishbein, 1994; Olano, (Anderson, 1992b; Chen, 1994; Everett, 1994; Buller, 1999; Comer, 1999). 2003a, 2003b). Although severe cases often affect older persons, children For human monocytotropic ehrlichiosis, the sensitivity of PCR is reported are also susceptible to the illness (Schultze, 1997). The median duration of as 79%–100%, and for granulocytotropic anaplasmosis caused by A. phago- illness in a large CDC series, including treated cases, was 23 days. Signs and cytophilum, 48%–86% (Anderson, 1992b; Everett, 1994). Lateness in the symptoms depict a systemic disease that has no clinically diagnostic fea- course, a lower level of ehrlichemia, and tetracycline treatment reduce the tures: fever (97%), headache (81%), myalgia (68%), anorexia (66%), nausea sensitivity of detection of ehrlichiae by PCR. Target genes that have been (48%), vomiting (37%), rash (6% at onset, 25% during the first week, and validated clinically include 16S rRNA (rrs), 120-kDa protein, groesl, dsb, 36% overall), regional lymphadenopathy (29%), cough (26%), pharyngitis nadA, and VLPT for E. chaffeensis, rrs and dsb for E. ewingii, and rrs, ank-1, (26%), diarrhea (25%), abdominal pain or tenderness (22%), photophobia msp2, and ftsZ for A. phagocytophilum (Dumler, 2004; Doyle, 2005). (27%), and confusion (20%) (Fishbein, 1994; Olano, 2003b). Severe com- Although it is in many cases a laborious task, identification of morulae in plications include adult respiratory distress syndrome, disseminated intra- peripheral blood neutrophils provides a diagnosis of human anaplasmosis vascular coagulation, and renal insufficiency. Clinical laboratory findings or ehrlichiosis and can be performed in any clinical laboratory. It is a more include leukopenia (60%), thrombocytopenia (68%), and elevated hepatic sensitive approach for A. phagocytophilum infection (30%–80%) than for transaminases (86%). CNS involvement manifested by seizures and coma E. chaffeensis (7%–17% in immunocompetent patients and a very high has been documented by cerebrospinal fluid (CSF) pleocytosis, increased proportion of immunocompromised patients [Hamilton, 2004]). It is protein concentration and E. chaffeensis in CSF, and the presence of cerebral important to avoid false-positive interpretation caused by toxic granula- lesions at autopsy (Dunn, 1992; Ratnasamy, 1996; Walker, 1997a). Severity tions, Döhle bodies, superimposed platelets, apoptotic bodies, or contami- is age dependent (Olano, 2003a). In immunocompromised patients, includ- nant particles. Immunohistochemical identification of E. chaffeensis can be ing those with the acquired immunodeficiency syndrome (AIDS), human performed in tissue specimens (Dumler, 1993a; Yu, 1993). monocytotropic ehrlichiosis can be an overwhelming infection with massive Serologic diagnosis is the usual approach to the diagnosis of human56 growth of ehrlichiae and a fatal outcome (Paddock, 1993; Walker, 1997a). ehrlichiosis, using cell culture–propagated E. chaffeensis and A. phagocyto- Mild infections have also been documented. philum antigens in IFA assays (Nicholson, 1997; Childs, 1999; Walls, After entry via tick bite, E. chaffeensis spreads by lymphatic and/or 1999; Olano, 2003b). This method is very sensitive for the demonstration hematogenous routes. Ehrlichial morulae have been identified in mono- of seroconversion to a titer of 1 : 64 or greater 2–4 weeks after disease cytes and macrophages in the bone marrow, peripheral blood (rarely), onset. The expected serologic result on acute serum is absence of detected hepatic sinusoids, spleen, lymph nodes, meninges, kidney, gastrointestinal antibodies. Thus, treatment should be initiated empirically on the basis tract, and epicardium (Dumler, 1993a; Walker, 1997a; Sehdev, 2003). Bone of clinical and epidemiologic factors and should not be withheld pending marrow examination frequently reveals granulomas, myeloid hyperplasia, laboratory confirmation. Opinion as to a diagnostic single serum titer for and megakaryocytosis. Other reported lesions include perivascular lym- E. chaffeensis ranges from 1 : 64–1 : 256. Cross-reactivity of A. phagocyto- phohistiocytic infiltrates in the kidney, meninges, brain, and heart; inter- philum and E. chaffeensis is observed in approximately 20% of patients stitial mononuclear pneumonitis; foci of apoptosis-like cell death in the with human monocytotropic ehrlichiosis and human granulocytic ana- liver, lymph node, and spleen; diffuse reticuloendothelial hyperplasia; plasmosis. Thus, particularly in geographic regions where these infections erythrophagocytosis; and cholestasis. overlap and, indeed, if there is a possibility of travel-associated exposure, it is essential to determine antibody titers against both organisms. A Human Infection with Ehrlichia ewingii fourfold difference in titer determines the infecting agent. Cases with Recognized first as a canine pathogen in 1971, E. ewingii also infects white- twofold or less difference are classified as ehrlichiosis of indeterminate tailed deer and is transmitted by A. americanum ticks (Ewing, 1971; etiology. Anziani, 1990). It shares antigens with E. chaffeensis but infects mainly Distinguishing E. chaffeensis from E. ewingii serologically is more prob- neutrophils. A high proportion of infected patients are immunocompro- lematic because the latter has yet to be cultivated. Western immunoblot- mised, suggesting that immunocompetent patients may be relatively resis- ting is a useful research tool at present for distinguishing infection with E. tant to the illness (Buller, 1999; Paddock, 2001). chaffeensis with its distinctive 120-kDa protein and 28-kDa protein family from infection with A. phagocytophilum with its major 42–49-kDa protein Human Granulocytotropic Anaplasmosis patterns (Asanovich, 1997; Chen, 1997a, 1997b; Zhi, 1997). Serologic Thousands of cases of human granulocytic anaplasmosis have been docu- assays using these and other recombinant proteins show promise for future mented, with most cases reported in the upper midwestern (Wisconsin and development (Yu, 1999; Knowles, 2003). Minnesota) and northeastern states (New York, Connecticut, Rhode Island, and New Jersey) of the United States, but with confirmed autoch- Treatment thonous infections southward along the eastern seaboard and in California Doxycycline is the drug of choice for the treatment of these human and Europe (Bakken, 1994; Aguero-Rosenfeld, 1996; Petrovec, 1997; ehrlichioses (Bakken, 1994; Fishbein, 1994). The use of chloramphenicol Horowitz, 1998). Infection is transmitted by Ixodes scapularis, I. pacificus, is not recommended as it has been associated with a fatal outcome. Cell and Ixodes ricinus ticks. The white-footed mouse (Peromyscus leucopus) and culture studies show E. chaffeensis and A. phagocytophilum to be resistant to other small mammals are likely reservoir hosts in the United States, as are it and the commonly prescribed β-lactams, macrolides, aminoglycosides, red deer, sheep, goats, and cattle in Europe (Hodzic, 1998). The pathology and sulfonamide drugs (Brouqui, 1992; Klein, 1997; Branger, 2004). is poorly defined, with the observation of morula-containing neutrophils A. phagocytophilum is susceptible to rifampin and rifabutin in cell culture, in peripheral blood and various organs, infiltrates of reticuloendothelial and rifampin has been used to treat a limited number of pregnant women organs with foamy macrophages, multiorgan perivascular lymphohistio- and children successfully (Krause, 2003). cytic infiltrates, and focal hepatocellular apoptosis (Walker, 1997a). Fatal- ity may be associated with secondary opportunistic fungal and viral infections (Hardalo, 1995). INFECTIONS CAUSED BY COXIELLA BURNETII Human granulocytotropic anaplasmosis varies from asymptomatic to severe, with many diagnosed patients requiring hospitalization (Bakken, Structure and Function 1994). Infection is fatal in less than 1% of cases. The illness begins with C. burnetii is distant phylogenetically from other pathogenic rickettsiae chills, fever, headache, and myalgia. Thrombocytopenia occurs in most and is the only one classified in the γ-Proteobacteria. These gram- cases and leukopenia in nearly half. Hepatocellular injury is manifested as negative bacteria vary morphologically from rods to cocci, and by electron 1074
  • 11. microscopic examination, two distinct forms can be seen: large cells (0.5– Q fever. In chronic Q fever, antibodies to phase I are present at a higher1.2 μm) and small dense cells (0.5 μm), which have been proposed to titer (e.g., IgG-IFA anti–phase I titer of 1 : 800 or greater), and antibodiesrepresent a developmental cycle that includes a spore-like form. to phase II are generally equal to or lower than the phase I titer. An IgA Much emphasis has been placed on a laboratory phenomenon associ- response to phase I antigens is often observed in patients with chronicated with cultivation of C. burnetii by prolonged passage in cell culture or Q fever. A titer of 1 : 128 or greater against phase I antigen by the comple-eggs, namely, loss of the organisms’ ability to synthesize the entire LPS. ment fixation test is also considered diagnostic of chronic Q fever, althoughThis change from synthesis of the full to a truncated LPS, analogous to some patients have lower titers. Because of cross-reactivity of B. henselaethe conversion from smooth to rough phenotype by Enterobacteriaceae, and Bartonella quintana with C. burnetii, a serologic diagnosis of Bartonellahas been designated phase variation from phase I to phase II. Phase I is endocarditis should not be made until anti–C. burnetii titers have beenfound in nature and in infected persons and animals; phase II occurs in the determined (La Scola, 1996b). In Q fever endocarditis, the anti–C. burnetiilaboratory and is the result of deletions of genes without selective advan- titer is substantially higher than the anti-Bartonella titer. An IFA containingtage under conditions of passage outside of its hosts (Hoover, 2002). both C. burnetii and B. henselae effectively distinguishes the infecting bac- C. burnetii enters its target cell, the macrophage, by phagocytosis after terium (Rolain, 2003b).interaction with αvβ3 integrin and is highly adapted (e.g., synthesis of PCR assays have been developed against diverse target genes, andsuperoxide dismutase and acid phosphatase) to the acidic conditions in the during the first 2 weeks of acute Q fever, real-time PCR of serum is morephagolysosome, where replication by binary fission occurs. sensitive (24%) than IFA serology (14%) (Fournier, 2003). It is likely that PCR of blood or buffy coat would detect a greater proportion of cases withQ Fever Coxiella than serum.The name Q fever was derived from its unknown etiology when the clini- Other methods for the diagnosis of chronic Q fever endocarditiscoepidemiologic syndrome was first described as query fever. The ecology include immunohistologic staining (sensitivity 32%), electron microscopy,of C. burnetii includes silent infections in animals: many species of ticks, culture (sensitivity 64%), and PCR (sensitivity 75%) detection of C. bur-ungulates (particularly sheep, cattle, and goats), other mammals (including netii in a cardiac valve (Lepidi 2003). C. burnetii can be recovered from thecats and wild rabbits), fish, birds, and marsupials (Marrie, 1988, 1997). blood or infected cardiac valves by in vitro cultivation using a centrifugation-Humans usually are infected by inhalation, especially of aerosols that enhanced shell vial (human embryonic lung) cell culture system. Thisoriginate in infected birth products of domestic livestock and pets, and method can identify the presence of coxiellae within 7 days but should bepossibly also by ingestion of unpasteurized contaminated milk (Fishbein, attempted only within cell culture facilities approved for biohazard con-1992; Raoult, 2005). Many human infections occur as an occupational tainment level 3.disease among abattoir workers, farmers, and veterinarians (McQuiston,2006). However, urban nonoccupational cases are by no means rare in Treatmentsome populations in which they have been evaluated, such as among Doxycycline is effective in shortening the course of acute Q fever whenimmunocompromised patients in France (Brouqui, 1993). administered during the first 3 days after the onset of illness (Levy, 1991). PART 7 A majority of human infections are asymptomatic (Marrie, 1990). Acute Ciprofloxacin or a combination of ciprofloxacin and rifampin is alternativeillness is often a self-limited, undifferentiated febrile illness, pneumonia, medication for patients who cannot be treated with tetracycline. Treatmenthepatitis, or meningoencephalitis (Drancourt, 1991; Tissot Dupont, 1992; of chronic C. burnetii endocarditis requires prolonged administration ofBernit, 2002). Individual patients with myalgias, anorexia, and headache doxycycline and a quinolone, which often does not eradicate the infectionare unlikely to be investigated diagnostically for Q fever, even though this (Marrie, 2002). Successful treatment is indicated by a slow fall in anti–syndrome is the most likely clinical presentation of this infection and phase I IgG titer to below 1 : 200, when discontinuation of treatment canaccounts for a substantial proportion of patients with these symptoms in be considered. Cardiac valve replacement is often performed for hemody-some populations. Manifestations of Q fever pneumonia vary: Cough may namic nonproductive or absent, and the pneumonia may be severe and pro-gress rapidly or may be detected as multiple rounded or segmental radio-graphic infiltrates without pulmonary symptoms. Q fever hepatitis may INFECTIONS CAUSED BY ORGANISMS OFhave a clinical presentation similar to acute viral hepatitis or the pathologic THE GENUS BARTONELLApresentation of granulomatous hepatitis. Chronic Q fever is considered synonymous with C. burnetii endocar- Structure and Functionditis but occurs less frequently as infection of an aneurysm or vascular The genus Bartonella has been removed from the order Rickettsialesprosthesis or osteomyelitis (Marrie, 1990; Brouqui, 1993). Chronic Q fever (Brenner, 1993; Birtles, 1996). The human pathogens, B. quintana (theendocarditis usually involves previously damaged aortic or mitral valves as etiologic agent of trench fever, a major louse-borne disease in World Warsan afebrile illness that may manifest with heart failure, hepatospleno- I and II and among homeless persons), B. henselae (the etiologic agent ofmegaly, changing cardiac murmurs, and weight loss. Disease associated cat scratch disease), Bartonella elizabethae and Bartonella vinsonii (associatedwith circulating immune complexes includes vasculitis-based purpuric rash with infective endocarditis), and Bartonella bacilliformis (a sandfly-or glomerulonephritis. transmitted bacterium that causes febrile acute hemolytic anemia and The pathology of acute Q fever includes mixed interstitial-alveolar- chronic verruga peruana cutaneous lesions in South America), have beenbronchiolar pneumonia with mononuclear inflammatory cells and granu- cultivated in blood-enriched media in the presence of 5% carbon dioxidelomatous inflammation of the liver and bone marrow (Walker, 1988b). (CO2) (Walker, 2006). These facultative intracellular gram-negative bacilliQ fever granulomas often contain a clear central vacuole and a surrounding do not produce acid from carbohydrates and usually reside within eryth-ring of fibrin, as well as epithelioid macrophages. These doughnut granu- rocytes in their natural mammalian hosts. Among numerous describedlomas are neither pathognomonic lesions nor the only form of granuloma species of Bartonella, Bartonella clarridgeiae is a suspected second agent ofthat occurs in the liver and bone marrow of Q fever patients. Involved cat scratch disease (Kordick, 1997).cardiac valves in Q fever endocarditis have a small vegetation and showmixed subacute and chronic inflammation with many foamy macrophageshaving the cytoplasm filled with C. burnetii (Lepidi, 2003). Cat Scratch Disease, Bacillary Angiomatosis, and Bacillary PeliosisLaboratory Diagnosis B. henselae is transmitted to humans by the scratch or bite of infectedThe laboratory diagnosis of Q fever is most often accomplished by dem- kittens, which are bacteremic for many months while appearing healthyonstration of antibodies to C. burnetii (Fournier, 1996, 1998). Serologic (Tappero, 1993; Chomel, 1995; Bergmans, 1997; Heller, 1997). Bacteriamethods employ both phase I and phase II antigens and often evaluate are transmitted from cat to cat by the cat flea (Chomel, 1996; Higgins,class-specific antibody production. Enzyme immunoassay and indirect IFA 1996). The nature of the disease is largely host determined. Among immu-tests are highly specific and are more sensitive than complement fixation. nocompetent hosts, 80% are younger than age 21 years and present withIn acute Q fever, antibodies to phase II antigens appear earliest after infec- a cutaneous papule or pustule at the inoculation site and self-limitedtion, and antibodies to phase I may be detected as early as 2 weeks after regional lymphadenopathy. Less than 2% of patients suffer complicationsthe onset of illness. In general, acute Q fever is associated with high titers such as hematogenously disseminated involvement of the liver, spleen,to phase II antigens and lower titers to phase I antigens. By IFA, an anti– lung, bone, CNS, retina, conjunctiva, or skin (Liston, 1996; Wade, 2000;phase II IgG titer of 1 : 200 or greater and an anti–phase II IgM titer of Verdon, 2002). The histopathology of cat scratch disease lesions consists1 : 50 or greater have a sensitivity of 58% and a specificity of 92% in acute of granulomas surrounding stellate microabscesses. Among severely 1075
  • 12. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS immunocompromised patients, B. henselae infection is manifested by fever in chronic Q fever endocarditis, and Western immunoblotting after cross- and bacteremia, or by cutaneous or visceral angioproliferative lesions. absorption yields a definitive diagnosis if necessary (Houpikian, 2003). The latter are characterized by lobular vascular proliferations of plump Real-time PCR can also be used to establish the diagnosis of Bartonella endothelial cells with clusters of small capillaries surrounding ectatic capil- endocarditis (Zeaiter, 2003). laries, separated by edematous, mucinous, or fibrotic stroma containing clusters of neutrophils, neutrophil debris, and granular microcolonies of Treatment bartonellae. In the skin, these lesions are designated bacillary angiomatosis; Cat scratch disease usually is self-limited, but the lymphadenopathy in the liver and spleen, hepatic and splenic peliosis. Dissemination to other resolves more rapidly after azithromycin (Bass, 1999). Drugs of choice for sites may occur also. The angioproliferative lesions of B. henselae and the treatment of bacillary angiomatosis include doxycycline, erythromycin, B. quintana in immunocompromised patients are indistinguishable, and and azithromycin (Rolain, 2004). Bartonella endocarditis has a more favor- they are similar to the verruga peruana of B. bacilliformis (Koehler, 1997). able outcome when treated with an aminoglycoside (Raoult, 2003). B. henselae, B. quintana, B. vinsonii subsp. berkhoffii and subsp. arupensis, Relapses may occur, requiring retreatment or even long-term maintenance B. alsatica, B. koehleri, and B. elizabethae have been documented as agents therapy. Ciprofloxacin is currently preferred for treatment of Oroya fever. of infective endocarditis (Drancourt, 1995; Roux 2000; Avidor, 2004; The difficulty of treating an intraerythrocytic bacterium such as B. quin- Fenollar, 2005; Raoult, 2006: Jeanclaude, 2009). tana in humans is evident in the lack of bactericidal activity of doxycycline, fluoroquinolones, and β-lactams, and an inability to achieve bactericidal Trench Fever and Bacillary Angiomatosis intraerythrocytic levels of gentamicin, the most active antimicrobial agent B. quintana causes prolonged bacteremia in convalescent humans, (Rolain, 2000). Chronic B. quintana bacteremia is cleared by gentamicin the apparent reservoir. Infections were recognized to be transmitted for 14 days, followed by doxycycline for 28 days (Foucault, 2003). Verruga from person to louse (Pediculus humanus corporis) to another person peruana is treated with oral rifampin. in front-line trenches during World War I (Bruce, 1921). Among French homeless persons, 14% are bacteremic, of whom 80% are afebrile (Brouqui, 1999). MYCOPLASMAL INFECTIONS Louse feces laden with B. quintana are scratched into the skin, and Mycoplasmas were proved to cause human disease in 1962, when one approximately 8 days later, an illness of variable severity begins. Manifesta- mycoplasma (subsequently named Mycoplasma pneumoniae) was recognized tions include fever, generally lasting less than a week, headache, myalgias, as the etiologic agent of primary atypical pneumonia (Chanock, 1962). pretibial pain, and an evanescent macular rash. Relapses often occur at Mycoplasmas are the smallest free-living organisms. They are pleomor- 4- or 5-day intervals. Bacteremia persists for weeks, months, or longer, phic, ranging from spherical cells 0.2 μm in diameter to filaments 0.1 μm serving as a source of infecting lice, even when the person feels relatively wide by 1–2 μm long. Most are facultative anaerobes that replicate by healthy. Cases occur at present in alcoholic and homeless populations in binary fission. Mycoplasmas are unique among bacteria because they have American and European cities (Spach, 1995; Foucault, 2002). no cell wall. They are unable to synthesize cell wall precursors, and they56 require cholesterol and related sterols for membrane synthesis. Mycoplas- Oroya Fever and Verruga Peruana mas also lack the enzymatic pathways for purine and pyrimidine synthesis South American bartonellosis, manifested as an acute illness called Oroya and, for this reason, require complex media (such as beef heart infusion fever, or as chronic cutaneous lesions called verruga peruana, is transmitted broth supplemented with horse serum, yeast extract, and nucleic acids) for by the bite of a Lutzomyia sandfly. Asymptomatic long-term human carriers growth in vitro. The potential pathogens, M. pneumoniae and the genital are the reservoirs of B. bacilliformis. After an incubation period of approxi- mycoplasmas (Mycoplasma hominis, Mycoplasma genitalium, Ureaplasma mately 3 weeks, Oroya fever begins insidiously with anorexia, headache, urealyticum, and Ureaplasma parvum), are discussed. Other mycoplasmas malaise, and low-grade fever, or abruptly with chills, high fever, headache, are part of the normal human flora, primarily of the respiratory and geni- and mental status changes. Bartonellae invade the red blood cells and cause tourinary tracts. erythrocytic changes that result in erythrophagocytosis and anemia. Verruga peruana, characterized by red to purple nontender nodules that appear in crops over 1–2 months and persist for months to years, MYCOPLASMA PNEUMONIAE follows Oroya fever or occurs without prior symptoms (Arias-Stella, 1986; Walker, 2006). Epidemiology Mycoplasma pneumoniae is found worldwide. Epidemics occur among con- Laboratory Diagnosis fined populations such as children in schools, families, and military recruits, Lysis release of intraerythrocytic bacteria followed by centrifugation and typically at 3–5-year intervals, and predominantly in late summer and fall. incubation at 35° C in a humid CO2 atmosphere on chocolate or Columbia In nonepidemic years, infections occur year-round and in general spread blood agar for longer than a month has been used to recover B. henselae slowly, possibly owing to the slow generation time of the bacterium and B. quintana from patients (Tierno, 1995). These Bartonella organisms (6 hours) and its low transmission rate, which apparently requires close are gram-negative bacilli, 0.2–0.5 μm in diameter and 1–3 μm long. contact with an ill person (Waites, 2004). During epidemics, however, B. henselae are oxidase, catalase, and urease negative and do not utilize infection may spread rapidly, and the occurrence of point-source outbreaks carbohydrates. Identification is accomplished by twitching motility in wet in which close and prolonged exposure is not recognized suggests that mounts, immunofluorescent staining, analysis of fatty acid composition, M. pneumoniae may be transmitted via aerosols. Rates of infection with DNA sequencing, or hybridization (Scott, 1996). PCR detects B. henselae M. pneumoniae are greatest in school-aged children and young adults, and DNA in 31% of lymph node biopsies and in 55% of lymph node aspirates pneumonia occurs most frequently in persons aged 5–20 years, especially (Bergmans, 1996). B. bacilliformis may be cultivated from blood by inocula- in those between the ages of 15 and 19 years. Infection with M. pneumoniae tion of Columbia blood agar supplemented with 5% defibrinated blood or is common before the age of 5 years but typically is asymptomatic or other blood- or hemin-supplemented media with detection of colonies produces a mild illness with coryza and wheezing but no fever or pneu- after an average of 18 days. monia (Fernald, 1975). Formerly, the diagnosis of cat scratch disease required a combination of clinical, epidemiologic, and pathologic criteria. Histopathologic studies, Pathogenesis and Pathology including Warthin-Starry stain and immunohistochemistry, have been M. pneumoniae, a surface parasite, colonizes the mucosa of the respiratory used to support the diagnosis of bacillary angiomatosis and cat scratch tract. Its ability to attach to respiratory mucosal cells, escape phagocytosis, disease. Oroya fever may be diagnosed by visualization of intraerythrocytic and modulate the immune system is essential to initiation of disease. Its bartonellae, appearing as cocci or bacilli, occasionally with curved or ring gliding motility may allow it to penetrate through respiratory secretions, forms, in peripheral blood carefully stained by the Giemsa method to avoid and its filamentous, flexible form with terminal attachment organelle may misinterpretation of artifacts. Diagnosis of B. henselae and B. quintana facilitate localization in crypts and folds of the host cell membrane and infections is usually accomplished by serologic demonstration of antibodies between microvilli and cilia, where it is protected from phagocytosis. by indirect immunofluorescence or enzyme immunoassay (Dalton, 1995b). Attachment of M. pneumoniae to host cells is mediated by the P1 protein, Serologic diagnosis of Bartonella endocarditis should include measurement which interacts with neuraminic acid–containing glycoproteins at the of antibody titers against C. burnetii, which may stimulate cross-reacting surface of the host cell membrane (Chandler, 1982; Geary, 1987; Waites, antibody titers against Bartonella (Maurin, 1997; Rolain, 2003a). Titers 2008). Hydrogen peroxide and superoxide produced by M. pneumoniae may against C. burnetii phase I are much higher than the anti-Bartonella titers injure mucosal cells, causing ciliostasis and sloughing of superficial cells 1076
  • 13. (Almagor, 1984). Inhibition of catalase (which breaks down damaging GENITAL MYCOPLASMASperoxides) in host cells by bacterium-generated superoxides makes the cellsmore susceptible to damage (Waites, 2008). An adenosine diphosphate Epidemiology(ADP)-ribosylating protein (named community-acquired respiratory dis- Ureaplasma species (U. urealyticum has been separated into U. parvum,tress syndrome toxin: CARDS TX) produced by M. pneumoniae has been formerly U urealyticum biovar 1, and U. urealyticum, formerly U. urealyti-identified and postulated to have an exotoxin function, as the protein has cum biovar 2) can be found colonizing the vagina and cervix in 40%–80%been demonstrated to induce vacuolization and ciliostasis in cultured host of adult women, and M. hominis can be found in 21%–53% of womencells (Waites, 2008). The target and exact cellular effects of the toxin (Waites, 2005). The frequency in males appears to be lower. Prevalenceremain to be elucidated. studies for M. genitalium are infrequent in the literature, but it appears to Host-related factors also are involved in the pathogenesis of M. pneu- be less common as a colonizer in asymptomatic individuals and is foundmoniae disease. The apparent high prevalence of M. pneumoniae infection with a frequency of around 1% (Takahashi, 2006; Manhart, 2007). Colo-in infants and young children, the mild nature of the disease in this age nization of infants with genital mycoplasmas can occur during passagegroup, and the occurrence of more severe illness during infection at a through the birth canal, but colonization appears to be temporary in manylater age suggest that severe disease may result from the host immune cases, and a lower rate of colonization has been noted in children (Klein,response to reinfection. M. pneumoniae has been demonstrated to induce 1969; Hammerschlag, 1978). The increase in colonization by mycoplasmascytokine production in vitro, suggesting that adherence of the bacterium after puberty indicates an association with sexual activity. In addition toto respiratory epithelial cells results in cytokine production, which in passage through the birth canal, neonates can acquire infections due toturn might both recruit inflammatory cells, including lymphocytes, to Ureaplasma spp. and M. hominis hematogenously through the placenta orthe site of infection and modulate the activity of the recruited cells through an ascending infection, resulting in seeding of amniotic fluid(Waites, 2008). This cytokine production and influx of lymphocytes might (Waites, 2005).be involved in fighting the infection by destroying the infecting organismor, conversely, might result in immune hypersensitivity that damages host Clinical Manifestationscells. A more marked T cell immune response may result in more severe Although simple vaginal colonization with the genital mycoplasmas indisease (Waites, 2008). Moreover, extrapulmonary manifestations of pregnant women is not associated with disease, the presence of myco-disease (discussed later) are suspected to be immune mediated. The inter- plasma (primarily Ureaplasma spp. and to a lesser extent M. hominis) in theaction of M. pneumoniae with the I antigenic determinant of human red placental membranes or amniotic fluid is consistently associated with cho-blood cells, which contains the necessary 2,3-sialylated poly-N-acetylga- rioamnionitis, preterm birth, and adverse perinatal outcomes associatedlactosamine sequences, may alter the I antigen, converting it into a non– with several neonatal disorders, including perinatal pneumonia and sepsisself-antigen that stimulates production of cold agglutinins. Other in preterm infants (Waites, 2005; Goldenberg, 2008). Both Ureaplasmaautoimmune antibodies produced during infection with M. pneumoniae spp. and M. hominis are associated with postpartum fever. Ureaplasma spp.(antibodies to lung, brain, smooth muscle, and lymphocytes) may have can cause urinary calculi and are a cause of nongonococcal urethritis PART 7similar derivations. (NGU) (Waites, 2005). M. hominis has been related to both pelvic inflam- Few descriptions of the pathologic findings of disease caused by matory disease (PID) and pyelonephritis and may have an association withM. pneumoniae are available, because most infections are self-limited and bacterial vaginosis (Waites, 2005). M. genitalium has been linked to NGUtissue is rarely obtained. In fatal cases, patchy areas of consolidation in males only relatively recently, but it is now firmly established as a sig-are found in the lungs. Histologic examination of involved foci shows nificant cause of the disorder and is the etiologic agent in approximatelybronchitis, bronchiolitis, and interstitial and alveolar pneumonitis with 25% of cases (Ross, 2006; Gaydos, 2009). Among women, M. genitaliumperibronchiolar collections of lymphocytes and plasma cells, accompanied has shown an association with cervicitis, endometritis, PID, and tubalby macrophages and neutrophils if cellular necrosis is present. infertility (Haggerty, 2006; Short, 2009).Clinical ManifestationsThe most common manifestation of disease caused by M. pneumoniae is LABORATORY DIAGNOSIStracheobronchitis, which occurs in about half of infected patients. After anincubation period of several weeks, sore throat, cough, coryza, fever, head- Mycoplasma pneumoniaeache, myalgia, and sometimes conjunctivitis and myringitis are seen. The Specimens recommended for diagnosis of infection caused by M. pneu-infection may resolve or may progress to pneumonia, the frequency of moniae are throat swabs and serum, but bronchoalveolar lavage fluid,which is age dependent, with children aged 5–15 most likely to develop sputum, and lung tissue are acceptable. A nonspecific serologic test thatlower respiratory involvement (Baum, 2000; Waites, 2004). Chest radio- may provide useful information is detection of cold agglutinins, which aregraphs show unilateral lower lobe bronchopneumonia, or occasionally IgM antibodies against the I antigen of human erythrocytes. The coldbilateral feathery infiltrates. The peripheral white blood cell count is agglutinin response usually corresponds with the severity of pulmonarynormal early and rises as the disease progresses. Maculopapular or, less disease, as a titer of ≥1 : 32 is found with severe pneumonia, whereas agglu-commonly, vesicular skin eruptions occur in about 15% of cases a few days tinins are not detectable in mild disease (Waites, 2008). Cold agglutininsafter disease onset. Without antimicrobial therapy, fever resolves in 2–14 appear by the end of the first week or early in the second week of illnessdays, but malaise, cough, and radiographic abnormalities persist for 2–6 in at least half of infected persons, but their presence is not diagnostic ofweeks. In a small percentage of children and adults, pneumonia is severe infection with M. pneumonia, as they may also be seen with other bacterial,enough to warrant hospitalization; these patients may develop lung abscess, rickettsial, or viral infections.pleural effusions, secondary bacterial infections, bronchiectasis, or clinical Definitive diagnosis is based on detection of the organism, specificrelapse. antibodies, or specific nucleic acid sequences. To isolate M. pneumoniae, Extrarespiratory manifestations such as clinically apparent hemolytic special agar media, broth media, or a biphasic culture system is inoculatedanemia (typically with very high titers of cold agglutinins); erythema mul- and incubated in a sealed container for 3 weeks or more in 5%–10% CO2,tiforme, erythema nodosum, and urticaria; myocarditis and pericarditis; or anaerobically at 37° C. Cultures are examined microscopically (40×)and arthralgias, arthritis, acute glomerulonephritis, tubulointerstitial once or twice each week for typical spherical colonies with a dense centernephritis, and IgA nephropathy may occur, but are not frequent (Ponka, and thin outer layer (resembling a “fried egg”) embedded in the agar. Such1979; Cassell, 1981; Baum, 2000; Waites, 2004). M. pneumoniae has become colonies, consistent with M. pneumoniae, that demonstrate glycolysis (asrecognized, however, as having a significant association with CNS disor- demonstrated color change in the media pH indicator), β-hemolysis, andders, from minor to severe, including encephalitis and acute disseminated hemadsorption of guinea pig erythrocytes on further testing are presump-encephalomyelitis, with 6%–7% of patients hospitalized with M. pneu- tively M. pneumoniae. Definitive speciation usually requires staining withmoniae infection demonstrating neurologic manifestations (Waites, 2004). monoclonal antibodies using immunofluorescence or immunoperoxidase,Among 1988 patients referred to the California Encephalitis Project over immunoblotting, or PCR.a 9-year period, M. pneumoniae was implicated in 111 patients (5.6%) and Because isolation of M. pneumoniae may require several weeks, render-was the single most common implicated infectious agent (Christie, 2007). ing a culture clinically noncontributory, more rapid tests are most usefulMany cases of encephalitis associated with M. pneumoniae appear to be for diagnosis. Detection of specific IgM in a single serum sample is diag-relatively mild; however, severe cases of acute disseminated encephalomy- nostic of acute infection. If IgG is measured, acute and convalescent phaseelitis that may even result in fatality can occur in association with the samples must be tested, and the diagnosis is based on a fourfold or greaterinfection (Waites, 2004; Christie, 2007; Stamm, 2008). rise in titer. A variety of tests based on particle agglutination, EIA, or 1077
  • 14. CHLAMYDIAL, RICKETTSIAL, AND MYCOPLASMAL INFECTIONS immunofluorescence are available; EIA, particularly with membrane- solution. Colonies of Ureaplasma spp. have an irregular rather than circular bound assays, is the most popular (Waites, 2004). Serologic testing is umbonate morphology, are 15–60 μm in diameter, and stain dark brown not without problems as antibody titers vary with age, with children in 5 minutes. In U broth, Ureaplasma spp. produce a shift in pH, and the and younger individuals having consistently higher titers than adults color changes from yellow to red. A loopful of broth then is transferred (Daxboeck, 2002). Nucleic acid amplification tests can also provide rapid to agar plates and is streaked for isolation. diagnosis (Loens, 2003), but currently no commercial Food and Drug M. genitalium grows very slowly, similar to M. pneumoniae, with which Administration–cleared amplification test for direct detection of M. pneu- it shares many morphologic and antigenic similarities, and is difficult to moniae is available. Although time is required for patients to develop a isolate in culture. For clinical purposes, nucleic acid amplification is the serologic response, hence the sensitivity of serology early in infection may only practical test; although a commercial product does not exist at be low, as time from onset of symptoms increases, the sensitivity of PCR this time, many facilities have developed their own assays to detect the decreases (Thurman, 2009). Many experts consider the combined use of organism (Ross, 2006). No commercial serologic assays are available for PCR on respiratory specimens and serology the optimum approach to M. genitalium or any of the genital mycoplasmas, and the use of serology obtain maximum sensitivity in diagnosing infection (Christie, 2007; for these organisms is confined to research. Waites, 2008; Thurman, 2009). Genital Mycoplasmas TREATMENT Ureaplasma spp. and M. hominis may be recovered from urethral, vaginal, A tetracycline, macrolide, or fluoroquinolone is effective treatment for or endocervical swab specimens, blood, urine, abscess material, prostatic M. pneumoniae, and the macrolides, usually a newer drug such as azithro- secretions, semen, or tissues.Various culture systems may be used to isolate mycin or clarithromycin, are the agents of choice because of dosing con- the genital mycoplasmas (Clyde, 1984; Yajko, 1984; Wood, 1985; Phillips, siderations. Macrolide resistance has been reported in M. pneumoniae 1986). Traditionally, separate systems were used for each (U agar and isolates in Japan, and patients infected with these isolates suffered a pro- U broth for Ureaplasma spp. and H agar and H broth for M. hominis) longed course of infection relative to those infected with susceptible iso- because the optimal pH for growth of the two organisms differs (pH lates (Waites, 2008). Generally, Ureaplasma spp. are sensitive to tetracyclines, 5.5–6.5 for Ureaplasma spp. and pH 6–8 for M. hominis). However, single quinolones, and macrolides, with tetracycline resistance seen in approxi- culture systems are now available that effectively detect all of these species mately 10% of isolates (Waites, 2005). Resistance to the fluoroquinolones (Yajko, 1984; Wood, 1985; Phillips, 1986). Broth cultures are incubated appears to be unusual, and Ureaplasma spp. are resistant to clindamycin. aerobically in sealed test tubes. Agar cultures are incubated anaerobically M. hominis is susceptible to clindamycin and the newer quinolones but is or in an atmosphere of 5%–7% CO2 and observed daily under the micro- resistant to the macrolides. Some isolates also are susceptible to tetracy- scope. M. hominis also grows on sheep blood agar, producing nonhemolytic clines, although resistance to the tetracyclines is thought to be greater than pinpoint colonies, and in most broth blood culture media, although no in Ureaplasma spp., at approximately 40% (Waites, 2005). M. genitalium evidence of growth is visible. can be problematic, in that treatment with macrolides (azithromycin), Colonies of M. hominis, 200–300 μm in diameter with a typical fried-56 tetracyclines (doxycycline), or quinolones (ofloxacin, levofloxacin) can egg appearance, usually appear within 5 days. In broth containing phenol result in a significant number of failures; however, cases in which these less red and 0.1% arginine, M. hominis metabolizes arginine to ammonia, expensive agents fail appear to be effectively treated with moxifloxacin. causing a color change from yellow to red. U agar plates are observed daily Such a cascade treatment strategy is recommended by a number of studies for 4 days, and on day 4 are stained with one to two drops of CaCl2–urea (Ross, 2006; Bradshaw, 2008; Jernberg, 2008). SELECTED REFERENCES Centers for Disease Control and Prevention. Screening Peipert JF. Genital chlamydial infections. N Engl J Med Waites KB, Talkington DF. Mycoplasma pneumoniae and tests to detect Chlamydia trachomatis and Neisseria gon- 2003;349:2424. its role as a human pathogen. Clin Microbiol Rev orrhoeae infections. MMWR 2002b;51:RR-15. Provides an excellent overview of genital infections with 2004;17:697. Discusses nonculture tests, both amplified and nonampli- C. trachomatis, including epidemiology, screening strate- Provides an in-depth review of M. pneumoniae, includ- fied, for diagnosis of genital infection with C. trachomatis gies, and treatment. ing taxonomy, pathogenesis, clinical syndromes, diagnosis, and N. gonorrhoeae. Solomon AW, Peeling RW, Foster A, Mabey DCW. and treatment. Loens K, Ursi D, Goossens H, Ieven M. Molecular Diagnosis and assessment of trachoma. Clin Micro- Zinsser H, editor. Rats, lice, and history. New York: diagnosis of Mycoplasma pneumoniae respiratory tract biol Rev 2004;17:982. Little, Brown; 1935. infections. J Clin Microbiol 2003;41:4915. Provides an excellent review of trachoma, including an Very readable historical account of the toll that disease Discusses various nucleic acid amplification methods that historical perspective and an overview of the developmental takes, especially in times of conflict. have been examined for direct detection of M. pneumoniae cycle, clinical presentation, and laboratory diagnosis. in respiratory specimens. Includes a discussion of specimen processing and quality control. REFERENCES Access the complete reference list online at 1078