Intro to Viruses

Question 1

Characteristics of viruses

Answer 1

• Small
• Non-cellular
• Can only reproduce inside host cell
• Tissue tropism: only infect specific host cell types

Question 2

Classification of Viruses

Answer 2

• Virion shape
• Presence/absence of envelope
• Genome structure
• Mode of replication

Question 3

Describe virion structure

Answer 3

• Nucleic chad inside protein capsid - protection

- Surrounded by lipid envelope with spike projections (targets for vaccines or identifying virus)

Question 4

Stages in virus replication

Answer 4

1. Attachment to cell wall
2. Uncoating - lipid envelope removed and virus enters in protein cashed
3. Rplication of own viral DNA
4. mRNA synthesis
5. Protein synthesis producing viral proteins

Question 5

What is required for viral culture?

Answer 5

Cell type that virus being tested for is able to infect - if changes are evident then culture is positive

Question 6

Examples of human virus infections

Answer 6

• Herpes
• Influenza
• Measles
• Norovirus

Question 7

Consequences of Viral infections

Answer 7

• Clearance (no, short or long term immunity)
• Chronic infection - HIV, hep B/C
• Latent infection
• Transformation - changes to human DNA causing cancer

Question 8

What is the host range

Answer 8

• Some only infect humans - smallpox, measles

- Some also infect animals/birds - transmission of novel virus to human

Question 9

What can coinfection of human/animal lead to?

Answer 9

Recombination and generation of a new strain

Question 10

Explain concept of latency

Answer 10

• After primary infection, viruses can lie dormant in cells

- Full viral genome retain in host cell but expression restricted but can be reactivated

Question 11

Viruses and cancer

Answer 11

Viral infections may lead to cancer

Question 12

How do viral infections lead to cancer?

Answer 12

Transformation:

• Virus can alter cell cycle control
• Alters apoptosis
• Cause persistent inflammatory process which leads to cancer via reactive oxygen species

Question 13

Principles of antiviral therapy

Answer 13

• All virustatic, none virucidal
• Limited viral proteins for antivirals to target as use host cell enzymes to replicate
• Non-toxic to host cell
• Few infections

Question 14

What can antivirals be used for?

Answer 14

• Prophylaxis
• Pre-emptive surgery - infection but no symptoms
• Overt disease
• Suppressive therapy - keep viral replication beneath rate cause causes tissue damage

Question 15

Methods of prevention of Viruses

Answer 15

• Immunisation (vaccine or passive imm. with Ig)
• Prophylactic treatment post exposure
• Infection prevention of control
• Bood / tissue / organ screening
• Antenatal screening

Question 16

Outline infection prevention & control measure

Answer 16

• Isolation of asymptomatic patients
• PPE
• Safe use and disposal of sharps

Question 17

Properties of viruses that can be potentially eradicated

Answer 17

• No animal reservoir or ability to amplify in environment
• Clearly identifiable
• No chronic carrier state
• Efficient and practical intervention i.e. vaccination

Question 18

Examples of viruses that have been eradicated

Answer 18

Smallpox, measles, polio