Influenza

Question 1

Decribe the structure of the influenza virus

Answer 1

Orthomyxovirus

Spherical, enveloped

Contain RNA

Question 2

Differentiate between influenza A and B viruses.

Answer 2

• A:
  
  • Usual cause of epidemics and pandemic
  • Live and multiply in many different animals
    
    • Birds= main animal reservoir
• B:
  
  • Less severe disease, smaller outbreaks
  • Predominantly in humans
  • Burden of disease= mostly children

Question 3

How is influenza transmitted?

Answer 3

Respiratory route

1. Small particles aerosols- remain suspended in air many hours
2. Larger particles/droplets- fall to ground within 3m of infected person
3. Viral particles landing on surfaces

Question 4

What are the 3 barriers to entry into the respiratory route for influenza?

Answer 4

1. Respiratory epithelial cells= covered by thick glycocalyx and tracheobronchial mucus- trap particles
2. Ciliated respiratory epithelial cells - sweep mucus up tract- then swallowed
3. In lung- immunologic defense
   
   1. Secretory IgA
   2. NK cells
   3. Macrophages

Question 5

How does the influenza virus enter the cells?

Answer 5

Receptor mediated endocytosis

Question 6

What are the symptoms and potential complications of influenza?

Answer 6

Question 7

What is the incubation period for the influenza A virus?

Answer 7

1-5 days

Question 8

How is influenza diagnosed?

Answer 8

Specific tests for influenza virus- eg nasopharyngeal swab

Question 9

How is influenza treated?

Answer 9

1. Antivirals - inhibit viral uncoating after uptake
   
   1. Rimantadine
   2. Amantadine
2. Neuraminidase Inhibitors
   
   1. Oseltamivir (Tamiflu)
   2. Zanamivir (Relenza)
3. Prevention
   
   1. Formalin- vaccine
   2. Quadrivalent vaccine- nasal spray

Question 10

What is antigenic drift?

Answer 10

Minor changes in the genes of the flu viruses that occur gradually over time- cause seasonal epidemics

Eg changes to hemagglutin and neuraminidase proteins required for replication of influenza virus

Question 11

How is it that flu is potentially fatal?

Answer 11

1. Immune system overreacts- T-cells attack and destroy the tissues where virus is replicating esp lungs
2. Opportunistic secondary infection eg any strep/staph species) - usually lungs