Introduction to Viruses

Question 1

Describe the possible shapes of a virus

Answer 1

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

Complex: Neither helical or icosahedral

Question 2

What are obligate intracellular pathogens?

Answer 2

only replicate inside host cell

Ex. Viruses

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

Complete, infective form of virus, outside host cell, core RNA and capsid

Question 5

What encapsulates the nucleic acid of a virus?

Answer 5

protein capsid

Question 6

What surrounds the protein capsid?

Answer 6

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 infectious agent - occurs when a vector bites or touches a person
Zoonotic (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 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 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 restricted (produces few antigen and no viral particles)

Question 13

What can reactivation cause?

Answer 13

May or may not cause disease

Question 14

When is reactivation most likely to occur?

Answer 14

immunocompromisd - most severe

Question 15

How can some viral infections lead to cancer?

Answer 15

Modulation of cell cycle control - driving cell proliferation
Modulation of apoptosis
Persistent inflammatory processes lead to cancer via reactive oxygen species

Question 16

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

Answer 16

Whole organism - microscopy
Antigen, nucleic acid - PCR
Immune response to pathogen (recent/prior infection or response to vaccination)

Question 17

What is common in all antiviral agents?

Answer 17

Virustatic
None are virucidal
Only inhibit virus growth and replication

Question 18

Why are their limited target proteins for antiviral drugs?

Answer 18

Virus uses host cell enzymes to replicate

Question 19

Give a reason why antiviral therapy is not used very commonly

Answer 19

Toxicity to host cell

Question 20

Give examples of when antiviral therapy may be used

Answer 20

Prophylaxis (prevents infection)
Pre-emptive therapy (evidence of but no symptoms)
Overt disease
Suppressive therapy

Suppressive therapy (keeps viral replication below 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)
Prophylaxis after exposure
Screening - blood, tissues and organs
Antenatal screening
Infection prevention and control measures (isolation of symptomatic patients, PPE, Safe disposal of sharps)

Question 22

When can viruses be eradicated?

Answer 22

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