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Flashcards in Virology Deck (15):

What is viral recombination?

Exchange of genes between 2 chromosomes by crossing over within regions of significant base sequence homology.


What is viral reassortment?

When viruses with segmented genomes (e.g., influenza virus) exchange segments. High frequency recombination. Cause of worldwide influenza pandemics.


What is viral complementation?

When 1 of 2 viruses that infects a cell has a mutation that results in a nonfunctional protein. The nonmutated virus "complements" the mutated one by making a functional protein that serves both viruses.


What is viral phenotypic mixing?

Occurs with simultaneous infection of a cell with 2 viruses.

Genome of virus A can be partially or completely coated with the surface proteins of virus B. Virus B protein cote determines tropism (infectivity) of the hybrid virus. However, progeny from this infection will have type A coat derived from virus A's genetic material.


What is the effect of live attenuated viruses?

What viruses are vaccinated in this way?

Induce humoral and cell-mediated immunity. Can be virulent on rare occasions.


Live attenuated - smallpox, yellow fever, chickenpox (VZV) Sabin polio virus, MMR, Influenza (intranasal)


"Live! One night only! See small yellow chickens get vaccinated with Sabin and MMR! It's incredible!"

MMR = Measles, mumps, rubella. Can be given to HIV-positive patients who don't show signs of immunodeficiency.


What immunity do killed viruses elicit?

What viruses are vaccinated in this way?

Killed/inactivated: Only humoral immunity, but stable.


Rabies, Influenza (injected), Salk Polio, and HAV.

SalK = killed

RIP Always


What viruses are vaccinated by a recombinant virus?

HBV (antigen = recombinant HBsAg)

HPV (types 6, 11, 16, 18)


What generalizations can you make about DNA viral genomes?

What are the exceptions?

All are dsDNA (like our DNA) except parvovirus "part of a virus". (Parvus = small)


All are linear except papilloma-, polyoma- and hepadnaviruses (circular)


What generalization can you make about RNA viral genomes?

All are ssRNA except Reoviridae.


All are ssRNA (like our mRNA) except repeato-virus (reovirus) is dsRNA.


What are the positive strand RNA viruses?

Retrovirus, togavirus, flavivirus, coronavirus, hepevirus, calcivirus, picornavirus.


I went to a retro toga party, where I drank flavored Corona and ate hippy California pickles.


What naked viruses are infectious?

Purified nucleic acids of most dsDNA viruses (except poxvirus and HBV) and positive-strand ssRNA viruses are infectious.


Naked nucleic acids of negative-strand ssRNA and dsRNA viruses are not infectious - require polymerases contained in complete virus.


Where do DNA viruses replicate?

The nucleus (except poxvirus)


Where do RNA viruses replicate?

The cytoplasm (except influenza and retroviruses)


What are the naked (nonenveloped) viruses?

Papillomavirus, Adenovirus, Parvovirus, Polyomavirus, Calicivirus, Picoronavirus, Reovirus, Hepevirus


Give PAPP smears and CPR to a naked Heppy (hippy).


Where do enveloped viruses acquire their envelopes?

From the plasma membrane when they exit.


Exception: Herpesviruses, acquire envelopes from nuclear membrane.