Lecture 1 Intro to VIR

Question 1

What is the eclipse period?

Answer 1

Period just after infection (usu. few hrs.) where there are no detectable virions.

Question 2

What is the generic replication cycle for a virus?

Answer 2

Adsorption (usually involves host cell surface receptor)

Penetration (i.e. entry)

Uncoating (beginning of the eclipse period

Synthesis (of viral NAs and prots)

Assembly of new virions (end of eclipse)

Maturation

Release

Question 3

Compare and contrast the terms SUSCEPTIBLE and PERMISSIVE

Answer 3

A SUSCEPTIBLE host cell expresses the surface prots req’d for viral entry

a PERMISSIVE host cell has the internal supplies/machinery to allow virus to replication successfully

Question 4

What are SYNCYTIA?

Answer 4

multinucleated cells that result from fusion of several cells 2° to infection w/ a virus that expresses fusion proteins on its envelope

Question 5

What is and what determines the HOST RANGE?

Answer 5

host range is the number of species a virus can infect; the high specificity of viruses to adsorb to a particular cell surface antigen

Question 6

What does TISSUE TROPISM mean? What causes it?

Answer 6

Tissue tropism refers to the particular tissues likely to be infected by a virus within a susceptible species (i.e. one that is w/in the HOST RANGE). IT is due to the high specificity of viruses to adsorb to a particular cell surface antigen

Question 7

What viruses cause incusion bodies? Where do they appear histologically?

Answer 7

Rhabdoviridae (Rabies)—Negri bodies in CYTOSOL

Pox—inclusion bodies (CYTOSOL)

Herpes—Inclusion Bodies (NUCLEUS)

Question 8

Describe the SYMMETRY, ASSEMBLY AND STABILITY OF SIMPLE (UNENVELOPED) NUCLEOCAPSID VIRUSES

Answer 8

Both DNA and RNA uneveloped viruses:

are icosohedral in symmetry and very stable in the environment (i.e. don’t require person-to-person direct transmission)

RNA: assembly is in cytosol—form crystals there

DNA: assembly is in nucleus—form crystals there

Question 9

What are the categories included in the Baltimore Virus Classificaiton Scheme? Give examples of each.

Answer 9

dsDNA (e.g. Adeno, Herpes, Pox), ssDNA (e.g. Parvo)

dsRNA (e.g. Reo), (+)ssRNA (e.g. Picorna, Toga), (-)ssRNA (e.g. Orthomyxo, Rhabdo)

ssRNA-RT (e.g. HIV), dsRNA-RT (Hepadna)

Question 10

With ssRNA viruses, which have infectious genome: (+)sense or (-)sense ssRNA?

Answer 10

(+) sense because it is oriented in the same direction as host mRNA molecules

Question 11

What are the 3 general patterns of pathogenesis?

Answer 11

a. No significant illness at site of infection but produces a viremia that allows infection of other tissues, which then results in illness. incubation = weeks (or months). Immunity will often last for decades or life.
b. Virus growth in cells at the site of virion entry into the body (usually mucosal surfaces) causes illness. Here the incubation period will be short (days). Immunity is largely dependent upon secreted IgA. Immunity is less effective than; may be only short term (3 to 10 years). But reinfection is generally milder.
c. Virus growth in cells at the site of virus entry causes no significant illness. The virus spreads to other tissues by a neural pathway. Again the incubation period will be longer.