Viral Pathogenesis

Question 1

How do viruses spread to the environment?

Answer 1

They must enter host to spread target cells

i.e. enter cells, replicate, and leave

Question 2

What are the common entry sites for viruses?

Answer 2

Respiratory tract
- replication sites = pharynx, larynx, tonsils, trachea, bronchi, alveoli

Alimentary tract

• must be able to withstand stomach/duodenum
• M cells often used due to site of antigen uptake for lymphoid sampling

Skin
- usually require breakage, i.e. bite, trauma

Mucous membranes

Question 3

What are localised infections?

Answer 3

Sites of entry, replication, and shedding are the same

e. g. influenza
- enters via RT, replicate in RT epithelia, she back into RT

Question 4

What are disseminated infections?

Answer 4

Sites of entry, replication, and shedding show variation

e. g. Measles
- enter via RT, infect dendritic cells, replicate in lymph nodes, spread via lymph and blood, replicates in vascular epithelia and she via RT

Question 5

List the different viral infections based on timings

Answer 5

Acute infection
Chronic infection
Latent infection
Subclinical infection
Insidious infection

Question 6

What would an acute infection be classified as?

Answer 6

Rapid onset, short lived infection that may be:

• non-persistent (body cleared of virus)
• persistent (body not cleared, disease may enter chronic/latent phases)

Question 7

What would a chronic infection be classified as?

Answer 7

Persistent infection with symptoms

Question 8

What would a latent infection be classified as?

Answer 8

Persistent infection without symptoms or spread

- infection may be reactivated later resulting in symptoms +/or spread

Question 9

What would a subclinical infection be classified as?

Answer 9

Persistent infection without symptoms, but may be transmitted

Question 10

What would a insidious infection be classified as?

Answer 10

Infection with long incubation period before symptoms occur

Question 11

List the mechanisms of damage

Answer 11

Via immune interactions

• apoptosis-induction by cytotoxic T cells
• free radicals
  
  • produced by phagocytes in damaged tisuse
    
    • e.g. NO, superoxide
    • inhibit replication but cause damage

Direct mechanisms

• take over cell machinery for virus production
• cell lysis
• modification of host DNA
• immunosuppression