Influenza Virus Notes

Influenza Virus Overview

  • Pathogen with significant impact, causing annual epidemics.

Learning Goals

  • Understand how influenza causes disease and infection risks.

  • Recognize how the immune system responds to influenza.

  • Familiarize with treatment methods.

Types of Influenza Viruses

  • Influenza A: Main life-threatening virus; 10% annual infection rate in US and Canada; ~51,000 deaths/year.

  • Influenza B: Narrower host range; slower mutation.

  • Influenza C: Causes mild disease; limited spread.

  • Influenza D: Rare in humans; mainly affects swine and cattle.

Historical Pandemics

  • 1918 Spanish Flu: 20% global infection, bird strain origin.

  • 1958 Asian Flu & 1968 Hong Kong Flu: Significant outbreaks.

  • 2009 H1N1: Mild disease but high concern; new variants like H7N9 pose risks.

Cold vs. Influenza Symptoms

  • Cold: Mild symptoms, often no fever.

  • Influenza: Severe symptoms, high fever, prolonged duration.

Virus Structure

  • Lacks geometrical capsid; surrounded by matrix proteins and lipid envelope.

  • Hemagglutinin (HA) and neuraminidase (NA) are key surface proteins.

Viral Genome

  • Composed of 8 RNA segments, enabling antigenic variation through reassortment.

Hemagglutinin (H)

  • 18 subtypes; crucial for entry into host cells via receptor binding and fusion.

Infection Mechanism

  1. Virus entry via endocytosis.

  2. Viral RNA synthesis in the nucleus.

  3. Assembly of new virions at the host cell membrane.

  4. Release through neuraminidase activity.

Drift and Shift Mechanisms

  • Drifting: Minor mutations; yearly vaccine updates needed.

  • Shifting: Major structural changes; potential pandemics when mixed strains occur in pigs.

Vaccine Production

  • WHO meetings assess circulating strains for vaccine formulation, taking ~6 months to produce.

Future Vaccine Aspirations

  • Development of a universal vaccine targeting conserved regions (e.g., HA stalk) to enhance immune recognition and reduce annual shots.