Usmle Step 1 Fa Micro-Virology

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Recombination

Back 1

Exchange of genes b/w 2 chromosomes by crossing over w/in regions of significant base sequence homology

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Reassortment

Back 2

When viruses w/segmented genomes exchange segments. High frequency recombination. Cause of worldwide pandemics.

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Complementation

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When 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein. The non mutated virus complements the mutated one by making a functional protein.

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Phenotypic mixing

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Occurs w/simultaneous infection of a cell with 2 viruses. Genome of virus A can be partially or completely coated (forming pseudovirion) w/ the surfac eproteins of virus B. Type B protein coat determines the infectivity of the phenotypically mixed virus. However, the progeny from this infx have a type A coat that is encoded by its type A genetic material.

Front 5

Live attenuated vaccines:
(a immune response
(b) pros
(c) cons
(d) examples

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(a) induce humoral and cell mediated immunity
(b) no booster needed
(c) have reverted to virulence on rare occassions; dangerous to give live vaccines to IC patients or their close contacts
(d) Measles, mumps, rubella, Sabin polio, VZV, yellow fever, small pox

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Killed vaccines
(a) immune response
(b) pros
(c) cons
(d) examples

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(a) humoral immunity
(b) stable
(c) boosters required
(d) Rabies, influenza, salk Polio, HAV vaccines

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Recombinant vaccine examples

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HBV (HBsAg), HPV (types 6, 11, 16, 18)

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Naked viruses

Back 8

Calcivivirus
Picornavirus
Reovirus
Parvovirus
Adenovirus
Papilloma
Polyoma

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Where to enveloped viruses usually acquire their envelopes? What is the exception?

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Plasma membrane except herpesviruses which acquire envelopes from nuclear membrane

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DNA enveloped viruses

Back 10

Herpesviruses, small pox

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DNA nucleocapsid viruses

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Adenovirus, papillomaviruses, parvovirus

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RNA enveloped viruses

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Influenza, paraingluenza, RSV, measles, mumps, rubella, rabies, HTLV, HIV

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RNA nucleocapsid viruses

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Enteroviruses (poliovirus, coxsackievirus, echovirus, HAV), rhinovirus, reovirus (rotavirus)

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HSV identification

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Tzanck test to detect multinucleated giant cells. Used for HSV-1, 2, and VZV.
Also see intranuclear Cowdry A bodies

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Negative stranded viruses

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Virion brings along its own RNA dependent RNA polymerase
Arenaviruses, Bunyaviruses, Orthomyxoviruses, Filoviruses, Rhabdoviruses

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Segmented viruses

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All are RNA.
Bunyavirus
Orthomyxovirus (influenza)
Arenaviruses
Reoviruses

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Viruses that give you spots

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Rubella: togavirus; 3d measles
Rubeola: paramyxovirus; measles
Herpesvirus; chickenpox and zoster
Poxvirus; smallpos (no longer present outside of labs)

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Hepatitis serologic marker description and interpretation of (+) test:
HBsAg

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Antigen found on surface of HBV; continued presence indicates carrier state

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Hepatitis serologic marker description and interpretation of (+) test:
HBsAb

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Ab to HBsAg; provides immunity to HBV

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Hepatitis serologic marker description and interpretation of (+) test:
HBcAg

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Antigen associated with core of HBV

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Hepatitis serologic marker description and interpretation of (+) test:
HBcAb

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Ab to HBcAg; positive during window period. IgM HBcAb is an indicator of recent disease. IgG HBcAb signifies chronic disease.

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Hepatitis serologic marker description and interpretation of (+) test:
HBeAg

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A second, different antigenic determinant in the HBV core. Important indicator of active viral replication and therefore transmissibility.

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Hepatitis serologic marker description and interpretation of (+) test:
HBeAb

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Ab to e antigen; indicates low transmissibility

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Opportunistic infections and diseases in AIDS: brain

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Cryptococcal meningitis, toxoplasmosis, CMV encephalopathy, AIDS dementia, PML (JC virus)

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Opportunistic infections and diseases in AIDS: eyes

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CMV retinitis

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Opportunistic infections and diseases in AIDS: mouth and throat

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Thrush (candida), HSV, CMV, oral hairy leukoplakia (EBV)

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Opportunistic infections and diseases in AIDS: lungs

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Pneumocystic jiroveci, TB, histo

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Opportunistic infections and diseases in AIDS: GI

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Cryptosporidiosis, MAC, CMV colitis, non Hodgkin lymphoma (EBV), Isospora belli

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Opportunistic infections and diseases in AIDS: skin

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Shingles (VZV), Kaposi's sarcoma (HHV-8)

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Opportunistic infections and diseases in AIDS: genitals

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Gential herpes, warts, cervical cancer (HPV)

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HIV associated infections and CD4 count: <400

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Oral thrus, tinea pedis, reactivation VZV, reactivation TB, other bacterial infx

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HIV associated infections and CD4 count <200

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Reactivation HSV, cryptosporidiosis, Isospora, disseminated coccidiomycosis, Pneumocystic pneumonia

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HIV associated infections and CD4 count: <100

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Candidal esophagitis, toxo, histo

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HIV associated infections and CD4 count <50

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CMV retinitis and esophagitis, disseminated MAC, cryptococcal meningoencephalitis

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Neoplasms associated w/HIV

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Kaposi's sarcoma (HHV-8), invasive cervical carincoma (HPV), primary CNS lymphoma, non hogdkin lymphoma

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Describe HIV encephalitis

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Late in course of HIV infection. Virus gains CNS access via infected macs. See microglial nodules wmultinucleated giant cells.

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Spongiform encephalopathy

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Prion disease
Creutzfield Jakob disease (rapid progressive dementia)
Kuru
Scrapie (sheep)
Mad cow disease
Pathologic prions have beta pleated sheet conformation that is resistant to proteinase digestion.