Introduction to Viruses

Question 1

Describe the possible shapes of a virus

Answer 1

Icosahedral : 20 faces
Helical: Protein binds around DNA/RNA in a helical fashion

Complex: Neither helical or icosahedral

Question 2

What are obligate intracellular pathogens?

Answer 2

Viruses that only replicate inside a host cell

Question 3

What can virus families be classified according to?

Answer 3

Virion shape / Symmetry
Presence or absence of envelope
Genome structure
Mode of replication

Question 4

What is a virion

Answer 4

Extracellular form of virus

Question 5

What encapsulates the nucleic acid of a virus?

Answer 5

A protein capsid

Question 6

What surrounds the protein capsid?

Answer 6

A lipid envelope containing spike projections

Question 7

What are the stages of virus replication?

Answer 7

Attachment
Uncoating
Replication of genomic nucleic acid
Protein synthesis
Virion assembly (insertion of virus proteins into a membrane)
Budding and release

Question 8

What are the methods of viral transmission?

Answer 8

Blood bourne
Sexual
Vertical
Faecal - oral
Droplet
Airborne
Close contact
Vector-borne (indirect transmission of an infectious agent - occurs when a vector bites or touches a person)
Zoonotic ( a disease that normally exists in animals but can infect humans)

Question 9

What might the coinfection of human and animal or bird strains in one organism lead to?

Answer 9

Recombination and generation of a new strain

Question 10

What are the consequences of viral infection?

Answer 10

No, short or long lasting immunity

Chronic infection

Latent infection (lysogenic part of the cell cycle - lies dormant)

Transformation - long term infection with altered cellular gene expression

Question 11

Describe the status of the viral genome during latency

Answer 11

Retained in host cell - expression is restricted (produces few antigen and no viral particles are produced)

Question 12

What can reactivation cause?

Answer 12

May cause disease

Question 13

When is reactivation most likely to occur?

Answer 13

In the immunocompromised - also where it is most severe

Question 14

How can some viral infections lead to cancer?

Answer 14

Modulation of cell cycle control - driving cell proliferation
Modulation of apoptosis
Reactive oxygen species mediated damage

Question 15

What are the three aspects of a virus that you can detect?

Answer 15

The whole organism
Part of an organism
the immune response to a pathogen

Question 16

What is common in all antiviral agents?

Answer 16

They are virustatic none are virucidal
Inhibit the growth of the virus
Stops virus replicating

Question 17

Why are there limited target proteins for antiviral drugs?

Answer 17

Virus utilises host cell enzymes in order to replicate

Question 18

Give a reason why antiviral therapy is not used very commonly

Answer 18

Toxicity to the host cell is common

Question 19

Give examples of when antiviral therapy may be used

Answer 19

Prophylaxis (prevents infection)

Pre-emptive therapy (evidence of infection- no symptoms)

Overt disease

Suppressive therapy - keeps viral replication below the rate that causes tissue damage

Question 20

What are the possible methods of prevention of viral infections?

Answer 20

Immunisation (vaccination - active and passive)
Prophylactic treatment post exposure
Infection prevention and control measures
Antenatal screening

Question 21

Viruses with what properties can be eradicated?

Answer 21

No animal reservoir
Clearly identifiable in diagnosis
No chronic state carrier
Efficient and practical intervention
Political and social support