introduction to viruses

Question 1

Describe the basic classification and characterisation of viruses

Answer 1

Characterisation:

• very small
• non-cellular
• can only replicate inside host cell
• tissue tropism: only replicate inside certain host cells

classified according to:

• mode of replication
• virion structure
• presence/absence of envelope
• genome

Question 2

outline the principle of viral culture

Answer 2

Need to be provided a host cell, not only nutrients in order to divide.
Need an atmosphere with 5% Co2
Can detect via whole organism, part of organism e.g. antigen, DNA or via immune response e.g. antibodies.

Question 3

Describe examples of human virus infections of major importance.

Answer 3

• Zoonotic- Rabies
• Vector-borne- Malaria
• Sexual- HIV
• Droplet- influenza
• Blood-borne- Hep C
• Airborne- measles
• Vertical- Hep B
• Faecal-oral- Polio
• close- contact- Herpes simplex

Question 4

Describe the structure of viruses

Answer 4

-Genetic material in coil.
-Surrounded by polymerases
-surrounded by protein capsule
surrounded by lipid envelope with spike projections

Question 5

Describe how viruses replicate

Answer 5

1- attach to host cell
2-uncoating of envelope
3-replication of genome
4- production of new virus protein
5-reassembly of virion
6-release

Question 6

Explain the concept of host range in relation to viruses

Answer 6

viruses are only able to replicate within certain host tissues

Question 7

Describe the consequences of a viral infection

Answer 7

• clearance with no ( Hep C) or some lasting immunity ( measles)
• chronic infection e.g. HIV
• latent infection
• Transformation

Question 8

Explain the concept of viral latency

Answer 8

some virus remains after primary infection but no new viral cells are produced. Can become reactivated when triggered.

Question 9

Describe the link between viruses and cancer and explain the mechanisms through which this results

Answer 9

• can lead to cancer by proliferation of cell division, inhibiting cell apoptosis, causing continuous inflammation which leads to release oxygen species

Question 10

Describe the indications for and principles of anti-viral therapy

Answer 10

-It is virustatic not virucidal
-As viruses invade host cells- there are not many antiviral proteins available
-Side effects are common
used for:
-prophylaxis- prevention
-suppression- when chronic
-overt
-pre-emptive treatment- when virus presence is known but before symptoms present.

Question 11

Describe how to prevent viral infections and explain how viruses can be eradicated

Answer 11

Can be prevented:

• immunisation: Vaccination or by treatment via immunoglobulin
• infection prevention methods
• blood and antenatal screening
• prophylactic treatment after infection

Can be eradicated:

• through social/political help
• when no animal remnants
• no carrier states
• accurate tools are used.