Introduction to Viruses

Question 1

Explain the basic classification and characterisation of viruses.

Answer 1

Viruses are classified according to:
o Host Range
o Virion Structure and Morphology
o Structure and replication of virus genome nucleic acid

Question 2

Outline the principles of viral culture.

Answer 2

Since viruses require living cells to live, all cultures must take place in cell lines, tissues or intact animals. The cells are grown in a nutrient containing medium, in at atmosphere with 5% CO2.

Question 3

Describe examples of human virus infection of major importance.

Answer 3

o Respiratory - Influenza A Virus, Rhinovirus, Respiratory Syncytial Virus

o Gastrointestinal - Rotavirus

o Neurological - Enterovirus, Herpes Simplex Virus

o Tumours - Papillomavirus, Retroviruses

Question 4

Whats the diameter of a typical virus?

Answer 4

20 – 400 nm diameter

Question 5

Describe the basic structure of a virus

Answer 5

• Icosahedral: 20 faces, each an equilateral triangle
• Helical: protein binds around DNA/RNA in a helical fashion
• Complex: neither icosahedral or helical

Question 6

List possible routes of transmission

Answer 6

Blood-borne
Sexual
Vertical
Faecal-oral
Droplet
Airborne
Close contact
Vector borne
Zoonotic

Question 7

What are the 4 possible outcomes of infection?

Answer 7

Clearance
Chronic infection
Latent infection
Transformation

Question 8

What is viral latency?

Answer 8

Virus latency (or viral latency) is the ability of a pathogenic virus to lie dormant (latent) within a cell, denoted as the lysogenic part of the viral life cycle. A latent viral infection is a type of persistent viral infection which is distinguished from a chronic viral infection.

Question 9

Describe some mechanisms that viral infection can lead to cancer

Answer 9

o Modulation of cell cycle control (driving cell proliferation)
o Modulation of apoptosis (prevention of programmed cell death)
o Reactive oxygen species mediated damage (some persistent viral infections can cause persistent inflammatory processes which lead to cancer via reactive oxygen species

Question 10

How would you detect whole organisms?

Answer 10

• Microscopy

* Cell culture

Question 11

What can antiviral therapy be used for?

Answer 11

• Prophylaxis (to prevent infection)
• Pre-emptive therapy (when evidence of infection/replication detected, but before symptoms are apparent)
• Overt disease
• Suppressive therapy (to keep viral replication below the rate that causes tissue damage in an asymptomatic infected patient

Question 12

How can you prevent viral infection?

Answer 12

• Immunisation
• Vaccination
• Passive immunisation with immunoglobulin
• Prophylactic treatment post exposure
• Infection prevention & control measures
• Isolation of symptomatic patients
• Personal protective equipment
• Safe use and disposal of sharps
• Blood / tissue / organ screening
• Antenatal screening