Influenza virus is an RNA virus - There are 3 types: A, B and C of which A and B are the most common.

Influenza A

• Causes winter epidemics yearly
• In most patients: A common cause of bronchitis with marked systemic symptoms (flu)
• Can also cause exacerbations of chronic lung and cardiac disease (important cause of morbidity/mortality)
• Occasionally causes pandemics that affect healthy people - E.g. 1918-1920 killed 20 million

Epidemiology

• Affects 20% of children and 5% of adults worldwide each year
• Affects human, pigs, geese, duck, birds, chickens

Pathophysiology

• Influenza is an RNA virus, contains 2 surface proteins:
  • Haemagglutinin (H)
  • Neuraminidase (N)
• Human subtypes - H1N1, H1N2, H3N2
• Occasionally bird suptypes affect humans - called avian flu e.g. H5N1 (quite aggressive)
  • is sporadic so cant spread from person to person
• The virus acts by infecting and killing epithelial cells, releasing viruses to infect more cells and be coughed out to infect others

Vaccination

• Influenza is preventable by vaccine
• Annual for select groups:
  • Aged 65
  • Young children
  • Pregnant women
  • Chronic health conditions such as asthma, COPD, heart failure and diabetes
  • Healthcare workers and carers