Mechanism of Viral infection and pathogenesis

Question 1

How do humans not get infected by ‘many’ viruses?

Answer 1

• They are adapted to non-human hosts
• They are excluded by surface barriers
• Innate immunity prevents them establishing
• Our adaptive immune response has seen something similar

Question 2

What are the different general patterns of viral infection?

Answer 2

Question 3

What are inapparent infections?

Answer 3

= asymptomatic, without clear symptoms, requires that viruses be non-cytopathic and host-adapted

Question 4

How does virus infection of a host lead to disease?

Answer 4

1. Pathogenesis results from cell and tissue damage caused by the viral infection
2. On some occasions, the relative limited damage caused by the virus is made worse or even caused by the host’s immune system = immunopathology

• After acute infection, the tissue is repaired and cured, but only 80% so can lead later years to chronic inflammation and further problems like cancer - eg Hep C
• Viral clearance and disease is associated with generation and infiltration of CD8+ cells which attack infected cells and destroy them –> liver damage
• Dengue virus = greatest risk is a previous infection with a different serotype
• RSV - depresses inflammatory cytokine production, CD8+ responses and IgG production, meaning clearance is slow and development of memory is poor - enhances IgE production leading to asthma/allergy on re-exposure

Question 5

What is the importance of the adaptive immune system for controlling the severity of infections?

Answer 5

Vaccines prevent further disease as you have been exposed previously

Infections can generate powerful, long-live immunity like in influenza

• You make a T cell response against your last infection which should be effective against your next infection