Avian Influenza

Subtypes

• H1-15 and N1-9 have all been isolated
• Highly Pathogenic Avian Influenza (HPAI), caused by H5 and H7 isolates, is also known as Fowl Plague (FP) and is notifiable
  • Chinese poultry are currently the main reservoir for H5N1, not wild birds

Pathogenesis

• HPAI is defined by:
  • Heamorrhages
  • Diarrhoea
  • Sometimes nervous symptoms
  • Sudden death
• H5 spread by feces and infected viscera (kidney/spleen are 100X more infectious than feces)
• H7 and other viruses are carried by 6% of the wild bird population and outbreaks mirror migrating patterns
  • This poses significant risk to free-range flocks

Zoonotic potential

• A 2003 Dutch outbreak of a pathogenic H7 virus caused widespread conjunctivitis and flu-like symptoms with recovery among poultry workers
• Rural chinese children became infected with H5N1 via aerosol transmission, which was limited to upper respiratory symptoms and did not show horizontal spread

Control

• Prevention by proper hygiene and preventing contact with the wild bird population
• Isolation and cull of infected premises
• Firebreak cull in the case of uncontrolled spread
• Vaccination is not currently practiced for the following reasons:
  • An eradication policy prevents it
  • Vaccination favors the evolution of the virus, which might increase its virulence and drift