Introduction to Viruses

Question 1

Describe the possible shapes of a virus

Answer 1

Icosahedral : 20 faces, each an equilateral triangle
Helical: Protein binds around DNA/RNA in a helical fashion

Complex: Neither helical or icosahedral

Question 2

What are obligate intracellular pathogens?

Answer 2

Can only replicate inside a host cell

Viruses are these

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

Define virion

Answer 4

The complete, infective form of a virus, outside its host cell, with a core RNA and a capsid

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 syndromes associated with viral infections?

Answer 10

Respiratory
Neurological
Gastroenteritis
Hepatitis
Skin infections
Eye infections
Congenital abnormalities
Arthralgia - infection of a joint
Lymphadenopathy (disease affecting the lymph nodes)

Question 11

What are the consequences of viral infection?

Answer 11

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 12

Describe the status of the viral genome during latency

Answer 12

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

Question 13

What can does reactivation cause?

Answer 13

May or may not cause disease

Question 14

When is reactivation most likely to occur?

Answer 14

In the immunocompromisd - also where it is most severe

Question 15

How can some viral infections lead to cancer?

Answer 15

Modulation of cel cycle control - driving cell proliferation
Modulation of apoptosis - preventing programmed cell death
Reactive oxygen species mediated damage - infections can cause persistant inflammatory processes which lead to cancer via reactive oxygen species

Question 16

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

Answer 16

The whole organism - microscopy, part of the organism (antigen, nucleic acid - PCR (extraction of genetic material followed by amplification of a specific region) -
or the immune response to a pathogen (used to determine a recent infection, prior infection or a response to vaccination)

Question 17

What is common in all antiviral agents?

Answer 17

They are virustatic none are virucidal. This means they only inhibit the growth of the virus, stops the virus replicating

Question 18

Why are their limited target proteins for antiviral drugs?

Answer 18

Virus utilises host cell enzymes in order to replicate

Question 19

Give a reason why antiviral therapy is not used very commonly

Answer 19

Toxicity to the host cell is not uncommon

Question 20

Give examples of when antiviral therapy may be used

Answer 20

Prophyaxis (prevents infection)

Pre-emptive therapy (when evidence of infection is detected but symptoms are not yet apparent)

Overt disease

Suppressive therapy - keeps viral replication below the rate that causes tissue damage in asymptomatic infected patient, common in long term immunodeficiency patients.

Question 21

What are the possible methods of prevention of viral infections?

Answer 21

Immunisation (vaccination - active and passive)
Prophylactic treatment post exposure
Infection prevention and control measures (isolation of symptomatic patients, PPE, Safe disposal of sharps)
Screening - blood, tissue s and organs
Antenatal screening

Question 22

When can viruses be eradicated?

Answer 22

No animal reservoir or ability to amplify in the environment
Clearly identifiable in diagnosis
No chronic state carrier (so you don’t miss those who are infected)
Efficient and practical intervention
Political and social support