Influenza virus

Background

Microbiology

• Enveloped, single-stranded, negative-sense RNA virus in the Orthomyxoviridae family
• Four genera corresponding to influenza A through D
• Typed by hemagglutinin (HA) and neuraminidase (NA) proteins
  • Antigenic drift refers to small mutations
  • Antigenic shift refers to large changes from reassortment

Epidemiology

• Worldwide

• Seasonal in temperate climates, lasting from fall through spring and peaking in late winter
• Antigenic drift usually results in local outbreaks, while antigenic shift can result in epidemic or pandemics