Viruses

Question 1

Describe characteristics of viruses?

Answer 1

Small
Structure can either be : Icosahedral - 20 faces of equilateral triangles. Helical - protein binds around DNA/RNA. Or Complex. 
Can only replicate within a host 
Non-cellular
Protein capsule to protect DNA.

Question 2

How can viruses be classified?

Answer 2

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

Question 3

What are some common routes for viral infection?

Answer 3

Blood borne
Sexually transmitted
Vertical (mother to baby)
Faecal - oral 
Droplet
Airborne
Close contact
Vector borne (often mosquitos) 
Zoonotic (animal host)

Question 4

Give some examples of viruses that only infect humans?

Answer 4

Small pox

Measles

Question 5

What is a novel virus?

Answer 5

An unseen before virus that has other been isolated from its own reservoir or isolated as the result of spread to an animal or human host where the virus had not been identified before.

Question 6

What may lead to new strain of virus being produced?

Answer 6

Coinfection of human and animal or bird strains in one organism may lead to recombination and generation of a new strain.

Question 7

What is viral latency?

Answer 7

The reactivation of virus cells that have lain dormant within the host cells since the primary infection.

Question 8

What can increase viral latency?

Answer 8

Someone who is immunocompromised.

Question 9

In what way can a virus be detected?

Answer 9

Whole organism
Part of the organism - antigen, nucleic acid
Immune response to a pathogen - antibodies

Question 10

Describe some methods of preventing viral infection?

Answer 10

Immunisation - vaccination, passive immunisation with immunoglobulin.
Prophylactic treatment post exposure
Isolation of symptomatic patients 
PPE
Safe use and disposal of sharps
Screening

Question 11

What properties do viruses that can potentially be eradicated have?

Answer 11

No animal reservoir or ability to amplify in the environment
Clearly identifiable, with accurate diagnostic tool
No chronic carrier state
Efficient and practical intervention, e.g. vaccination
Political / social support

Question 12

What are some examples of viruses that have the potential to be eradicated?

Answer 12

Small pox (eradicated in 1979)
Measles
Polio

Question 13

What are the different types off virus pathogenic mechanisms?

Answer 13

Cell destruction following virus infection
Virus-induced changes to cellular gene expression
Immunopathogenic disease

Question 14

Where are the sites of viral entry on the body?

Answer 14

Respiratory tract
Alimentary tract
Urinogenital tract
Skin
Capillary
Arthropod 
Conjunctiva

Question 15

What is an acute infection?

Answer 15

Happens once in a localised specific site. E.g influenza

Question 16

What is a latent infection?

Answer 16

Virus stays in body after first acute infection and reoccurs. e.g herpes.

Question 17

What is a chronic infection?

Answer 17

Virus is always present in the blood. Continually exists but at low levels.

Question 18

What are the effects of influenza virus?

Answer 18

Virus infects cells of the respiratory tract
Destruction of respiratory epithelium
Secondary bacterial infections due to the changing of antigenic markers.
Altered cytokine expression leading to fever.

Question 19

What is antigenic drift?

Answer 19

Minor changes  (natural mutations) in genes of flu viruses, occurs gradually over time to generate antigenic variants.
Slow change.

Question 20

What is antigenic shift?

Answer 20

Abrupt major changes in virus antigenic structure.

Question 21

What are some characteristics of enterovirus infections?

Answer 21

70+ known
Arrives in the body through the gut.
Can lead to viraemia - if neuronal may cause paralysis.
E.g polio

Question 22

What are the main steps of the retrovirus replication cycle?

Answer 22

Attachment of virus 
Membrane fusion
Uncoat and unwind viral RNA
Viral DNA replaces human DNA
Leads to tumour formation.