6. VIRUSES • Less than ½ micron, usually MUCH
less
• DNA/RNA “CORE” (genome)
• Protein “CAPSID” (protein –NA “coat”)
• Sometimes a lipid “ENVELOPE”
• Limited number of genes coding for all
other structures
•NO consistent naming system
7. Respiratory
Adenovirus Adenoviridae DS DNA Upper and lower respiratory tract
infections, conjunctivitis, diarrhea
Rhinovirus Picornaviridae SS RNA Upper respiratory tract infection
Coxsackievirus Picornaviridae SS RNA Pleurodynia, herpangina, hand-foot-
and-mouth disease, SARS
Coronavirus Coronaviridae SS RNA Upper respiratory tract infection
Influenza
viruses A, B
Orthomyxoviridae SS RNA Influenza
Respiratory
syncytial virus
Paramyxoviridae SS RNA Bronchiolitis, pneumonia
8. Digestive
Mumps virus Paramyxoviridae SS RNA Mumps, pancreatitis, orchitis
Rotavirus Reoviridae DS RNA Childhood diarrhea
Norwalk agent Caliciviridae SS RNA Gastroenteritis
Hepatitis A virus Picornaviridae SS RNA Acute viral hepatitis
Hepatitis B virus Hepadnaviridae DS DNA Acute or chronic hepatitis
Hepatitis D virus Viroid-like SS RNA With HBV, acute or chronic
hepatitis
Hepatitis C virus Flaviviridae SS RNA Acute or chronic hepatitis
Hepatitis E virus Norwalk-like SS RNA Enterically transmitted
hepatitis
9. Systemic with Skin Eruptions
RNA Measles (rubeola)
Measles virus ParamyxoviridaeSS
RNA German measles (rubella)
Rubella virus Togaviridae SS
DNA Erythema infectiosum,
Parvovirus Parvoviridae SS
aplastic anemia
DNA Smallpox vaccine
Vaccinia virus Poxviridae DS
DNA Chickenpox, shingles
Varicella-zoster virus Herpesviridae DS
DNA "Cold sore"
Herpes simplex virus 1 Herpesviridae DS
DNA Genital herpes
Herpes simplex virus 2 Herpesviridae DS
10. Systemic with Hematopoietic Disorders
Cytomegalovirus Herpesviridae DS DNA Cytomegalic inclusion disease
Epstein-Barr virus Herpesviridae DS DNA Infectious mononucleosis
HTLV-I Retroviridae SS RNA Adult T-cell leukemia; tropical
spastic paraparesis
HIV-1 and HIV-2 Retroviridae SS RNA AIDS
Arboviral and Hemorrhagic Fevers
Dengue virus 1–4 Togaviridae SS RNA Dengue, hemorrhagic fever
Yellow fever virus Togaviridae SS RNA Yellow fever
Regional hemorrhagic
fever viruses
Filoviridae SS RNA Ebola, disease
Hantavirus SS RNA Korean, pneumonia
11. Warty Growths
Papillomavirus Papovaviridae DS DNA Condyloma; cervical carcinoma
Central Nervous System
RNA Poliomyelitis
Poliovirus Picornaviridae SS
DNA Progressive Multifocal
JC virus Papovaviridae DS
Leukoencephalopathy
(opportunistic)
Arboviral
encephalitis
viruses
RNA Eastern, Western,
Togaviridae SS
Venezuelan, St. Louis
12. BACTERIOPHAGES
PLASMIDS
TRANSPOSONS
• INFECT BACTERIA, but may
make a bacteria more difficult
to treat because it may
increase its “virulence”
or its susceptibility to
antibiotics
13. BACTERIA • GRAM staining with CRYSTAL VIOLET
–POSITIVE: THICK wall, ONE phospholipid layer
–NEGATIVE: THIN wall, TWO phospholipid
layers
• SHAPE
– COCCI (balls)
– BACILLI (rods)
• OXYGEN requirements
– AEROBIC (NEED O2)
– ANAEROBIC (do NOT NEED O2)
52. VIRAL • TRANSIENT, ACUTE, e.g. Measles,
Mumps, Polio, West Nile
• CHRONIC LATENT (HERPES
FAMILY), HSV, CMV, VZ
• CHRONIC (HEPATITIS), Hep A, B, C
• “TRANSFORMING” (Epstein-Barr
EBV, Human Papilloma, HPV)
65. VIRAL • CHRONIC (HEPATITIS), Hep. A, B, C
–A, Mildest, most universal
–B, Most dangerous in the acute
phase
–C, Most common cause of persistent
transaminitis
79. MYCOBACTERIA
(acid fast)
•Tuberculosis
• “Atypical” mycobacteria, the
most important of which is
MAC (Mycobacterium Avium
Intercellulare Complex, in HIV
patients)
• Leprosy
102. PROTOZOA
• MALARIA (Plasmodium sp., of which
falciparum is the most serius)
• Babesiosis, transmitted by deer tick
• Leishmaniasis
• Trypanosomiasis (sleeping sickness)
• Chagas disease (also a trypanosome)
• Entamoeba histolytica
Interest in “infectious” diseases caused by prions, i.e., NON-nucleic acid infectious agents, seems to be growing rapidly.
PrP, also called prion related protein, or protease resistant protein, is the infectious substance, and discovering it led to a Noble Prize in 1997.
PRI-ON itself Stands for PRO-teinaceous IN-fectious particle
BSE, or “Mad Cow” diease is the animal counterpart to human CJD or Creutsfeld-Jakob Disease, also commonly called Jakob-Creutsfeld Disease.
Vacoulization (sponginess) of CNS tissue is the consistent diagnostic finding (identify the vacuoles).
Nucleic acid “core”, capsid, envelope are the three common features of all viruses.
These primitive organisms are not often implicated in human diseases DIRECTLY, but indirectly.
Gram + bacilli (rods) and Gram – cocci
Remember the exception rule: Cocci are Gram+ EXCEPT for neisseria. Bacilli are Gram- EXCEPT for Bacillus (anthracis), Cornyebacterium, Clostridium, Lactobacillus, Listeria, Propionibacterium (acne) (ABCCLLP)
The OBLIGATE intracellular organisms, because they are obliged to live IN human cells to survive.
They have no cell walls, and no mitochondria, and therefore no ATP.
Fungi occur in tissues
ONE celled parasites are (Proto-zoans), multi-celled parasites (META-zoan) are worms (i.e., helminths) and arthropods
Classical (top 4) human helminth diseases
Ascaris life cycle
Taenia solium (cysticercosis) life cycle
T solium, T saginata, D latum, H nana,
Infectious agents spread geographically in the body exactly via the same routes which tumor cells do.
An infectious “agent” can attack a host cell directly, damage a host cell by its toxins, or by creating a host inflammatory response which damages host tissues
Main concepts of an infectious agent’s immune evasion.
By no surprise the common infections in immunosuppressed hosts theoretitally, parallels the common opportunistic infections seen in AIDS patients.
Common diagnostic techniques for identifying infectious agents.
The spectrum pattern of host responses parallels the entire spectrum of ALL inflammatory morphologies.
Granulomatous reactions are commonly seen with mycobacteria, fungi, sarcoid, foreign bodies, and rarely with almost anything.
Four types of viral infections: 1) Transient acute, 2) Chronic latent, 3) Chronic, 4) Transforming.
There is no consistent uniformity for viral taxonomy, so viral diseases can be classified according to their severity and/or abruptness of clinical expressions.
The common types of bacteria which infect humans. This is not at all a totally logical classification.
Morphologic types of fungi: yeasts and mold, independent of whether they are superficial, deep, or systemic
Protozoans are single celled organisms. Although metazoans technically are any multicellular organisms, they are often generally used synonymously with the word “worms”.
Classical viral infections which are TRANSIENT and ACUTE
Measles “giant” cell in measles pneumonia. The measles virus is a highly contagious airborne pathogen which spreads primarily via the respiratory system. The virus is transmitted in respiratory secretions, and can be passed from person to person via aerosol droplets containing virus particles, such as those produced by a coughing patient. Once transmission occurs, the virus infects the epithelial cells of its new host, and may also replicate in the urinary tract, lymphatic system, conjunctivae, blood vessels, and central nervous system
Parotitis, orchitis.
Poliovirus enters the body through the mouth, infecting the first cells it comes in contact with—the pharynx (throat) and intestinal mucosa. It gains entry by binding to a immunoglobulin-like receptor, known as the poliovirus receptor or CD155, on the cell surface.[26] The virus then hijacks the host cell's own machinery, and begins to replicate. Poliovirus divides within gastrointestinal cells for about a week, from where it spreads to the tonsils (specifically the follicular dendritic cells residing within the tonsilar germinal centers), the intestinal lymph nodes including the M cells of Peyer's patches, and the deep cervical and mesenteric lymph nodes, where it multiplies abundantly. The virus is subsequently absorbed into the bloodstream
Lymphocytic infiltrates in the “Virchow-Robbins” space IS classic for encephalitis.
The viruses in the Herpes/CMV family are CHRONIC and LATENT, often recurrent, and often travel along nerves and involve skin.
The hepatitis viruses are classifies as chronic
The arrowed “Councilman” bodies are rather diagnostic of viral (B) hepatitis.
The inflammatory pattern is periportal at first but can soon become PAN-lobular. Chronic hepatitis is chiefly periportal.
Transforming viruses cause tumors.
“Mono” is severe pharyngitism, adenopathy, splenomegaly, and hepatitis. The classical “mono” cells are really lymphocytes, and “heterophile” antibodies are fairly diagnostic.
Bridging the gap between infection and neoplasms, HPV viruses cause squamous cell cancer of the cervix.
Gram + bacilli (rods) and Gram – cocci
Remember the exception rule: Cocci are Gram+ EXCEPT for neisseria. Bacilli are Gram- EXCEPT for Bacillus (anthracis), Cornyebacterium, Clostridium, Lactobacillus, Listeria, Propionibacterium (acne) (ABCCLLP)
A strep infection in immunocompromised hosts, often the very old and very young.
“MAC” is the most common and serious “atypical” mycobacterium, seen very often in AIDS patients.
Necrotizing (i.e., caseating) granulomas filled with acid fast bacilli. This is CLASSIC for TB.
The acid fast stain for acid fast bacteria is also called the Ziel-Neilseon stain, or simply AFB stain
A leading cause of worlwide blindness, this keratoconjunctivitis affects 400 million people world wide.
The agent of RMSF is an obligate intracellular Rickettsia rickettsii organism carried by the tick Dermacentor andersoni, evoking microvasculitis and thrombosis of small vessels. Other rickettsia cause typhus.
Yeasts are balls, hyphae are long cylindrically shaped structures, often arising from yeasts
Without a doubt, by far, the most common and ubiquitous of all fungal agents.
Classical patterns of Candida, budding yeasts and PSEUDO-hyphae, staining very RED with the PAS stain and many others. The upper photo of budding yeasts could be from a culture because it has no tissue in it.
Both of these “mold” diseases can cause human diseases often in immunocompromised hosts.
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Ringworm of scalp
Tinea barbae
Ringworm
Tinea cruris, or jock itch
Athlete’s foot, or tinea pedis
Onychomycosis
These usually evoke granulomatous reactions in tissues. Histoplasmosis organisms are very small and often pack histiocytes, blastomycosis and coccidiomycosis are much larger round balls.
These should all be recognized as protozoal diseases.
Anopheles species mosquito of malaria
The various types of malaria are differntiated by the appearance of the RBCs and the forms of the parasites in them. Plasmodium falciparum is potentially the most deadly, and is gives rise to “blackwater fever”, i.e., marked hemoglobinuria and renal failure. Gametocytes (upper) are common to be seen in falciparum.
This is a very serious concern in Africa, in which the bite of the tsetse fly transmits the protozoan.
This is a classical diagnostic appearance on a routine blood smear. South American trypanosomiasis is called “Chagas” disease.
