Module 4

Question 1

What are viruses

Answer 1

molecular parasites (no metabolism), smaller than bacteria, genome + capsid + envelope (glycoproteins), no differentiative characteristics

Question 2

Life cycle

Answer 2

1. Virion adsorption to cell surface: tropism, neutralizes antibodies
2. Viral penetration of cell surface: endocytosis
3. Uncoating of viral genome: capsid is degraded
4. Primary transcription (gene expression)
5. Replication of viral genome
6. Secondary transcription: expression of progeny genomes
7. Packaging of progeny genomes
8. Release of progeny virions: lipid bilayer

Question 3

Phenotypic mixing/pseudotype formation

Answer 3

Viruses switching coats

Question 4

Field/street isolate

Answer 4

Directly from natural host

Question 5

Methods of controlling viral infection

Answer 5

vaccination (killed, live-attenuated, subunit via recombinant proteins) or antiviral drugs

Question 6

dsDNA virus families

Answer 6

• Papovarviridae: circular, icosahedral (HPV)
• Poxviridae: large + linear
• Adenoviridae: linear + icosahedral (hepatitis)
• Herpesviridae: linear + icosahedral (herpes, varicella)
• Hepadnaviridae: small + partially dd + icosahedral, replicate using reverse transciptase (Hepatitis B)

Question 7

ssDNA virus families

Answer 7

• Parvoviridae: small linear + non-segmented + icosahedral (Parvovirus B19)
• Anelloviridae: circular + non-segmented + icosahedra (torqueteno virus)

Question 8

Positive sense

Answer 8

mRNA goes directly into cell and translated directly

Question 9

Negative sense

Answer 9

converted to mRNA by RNA polymerase and then translated

Question 10

Segmented RNA

Answer 10

influenza, 2+ unique segments of nucleic acid, rapid evolution due to re-assortment (why there are new types every year)

Question 11

Positive sense ssRNA viruses – sub-groups

Answer 11

• Single large polyprotein: cleaved to release smaller enzymatic units (picornaviruses, flaviviruses)
• 2+ polyproteins: togaviruses, astroviruses, caliciviruses
• Numerous protein-coding sub-genomic RNAs from large genome: coronavirus

Question 12

Positive sense ssRNA viruses (7)

Answer 12

• Picornaviridae: small + survives severe conditions, polio and rhino
• Arteriviridae: vascular lesions, edema
• Togaviridae: arthropod-borne encephalitis, rubella
• Coronaviridae: LARGE, helical, upper and lower RT infections
• Hepeviridae: hepatitis E
• Astroviridae and Callciviridae: gastroenteritis
• Flaviviridae: insect vectors, hepatitis G/C, dengue, yellow fever

Question 13

Negative-sense RNA viruses (6)

Answer 13

• Paramyxoviridae: upper RT, measles, croup
• Rhabdoviridae: rabies (only virus where post-exposure immunization is helpful)
• Orthomyxoviridae: segmented genome, influenza A/B/C
• Bornaviridae: replicate in nucleus to take advantage of splicing machinery
• Bunyaviridae: hantavirus
• Filoviridae: Ebola

Question 14

dsRNA virus families

Answer 14

• Reoviridae: rotavirus
• Retroviridae: 2 identical strands of positive-sense mRNA (RNA – DNA – mRNA – Protein), AIDS

Question 15

Isolating virus families

Answer 15

Labile, symptoms may be from immune system not virus

Question 16

Cytopathic effect

Answer 16

viral infection causes structural changes of host cell

Question 17

Serological assays

Answer 17

• Neutralization assay: neutralizing antibodies + virus
• Hemagglutination assay: erythrocytes + virus
• Immunostaining: antisera linked to fluorescent dye
• Enzyme-linked immunosorbent assay (ELISA): capturing virus antibodies on solid surface, expose to substrate for detection

Question 18

Nucleic acid-based methods advantages

Answer 18

virus unable to be cultured, no antibodies (less $), inactivation of virus, reduced transportation concerns, indicates active infection