Introduction to Viruses

Question 1

How can viruses be classified?

Answer 1

• shape/ symmetry
• presence/ absence of envelope
• genome structure
• mode of replication

Question 2

Viral culture

Answer 2

sample placed in cell type that virus is known to infect, if the cell shows changes the sample is viral positive, if it doesn’t the sample is viral negative

Question 3

describe the structure of a virus

Answer 3

nucleic acid surrounded by protein capsid, with various other associated optional features

Question 4

name some modes of transmission used by viruses

Answer 4

• blood-borne
• sexual
• airborne
• water-borne

Question 5

describe the different outcomes of a viral infection

Answer 5

• clearance of virus (with no, short term, or long term immunity)
• chronic infection (e.g. HIV)
• latent infection (e.g. measles)
• transformation (e.g. influenza)

Question 6

explain concept of viral latency

Answer 6

following primary infection some viruses lie dormant in cells. reactivation of this virus can occur, although is more likely to occur in the immunocompromised

Question 7

what are the two main indirect ways in which viral replication leads to cancer

Answer 7

1. modulation of cell cycle control (driving cell proliferation)
2. Modulation of apoptosis (prevention of programmed cell death)

Question 8

All anti-viral drugs are virustatic rather than virucidal. what is meant by this?

Answer 8

they prevent viral replication rather than kill the virus

Question 9

prophylaxis

Answer 9

prevention

Question 10

examples of methods of prevention of viral infection

Answer 10

• immunisation
• prophylactic treatment post exposure
• IPC measures
• screening

Question 11

what properties are essential for a virus to become eradicated

Answer 11

1. no animal/ environmental reservoir
2. clearly identifiable with accurate diagnostic tool
   - no chronic carrier state
3. efficient and practical intervention method
4. political and social support