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Primary reference(s)

FAO, 2009. . Accessed 3 October 2020.

WHO, 2018. . Accessed 3 October 2020.

OIE, 2020. . Accessed 3 October 2020.

Additional scientific description

Avian influenza is transmitted by direct contact with infected birds or through contaminated environments (farms, markets, cages, vehicles, etc.) (OIE, no date a). Live poultry and poultry products trade and movements play an important role in national and cross-border spread. Certain avian influenza strains have also been shown to spread through migratory wild bird movements, sometimes over long distances (FAO, 2016, 2017). Biosecurity measures on farms and in live poultry markets are important to prevent disease introduction or spread (FAO, 2015).

Type A influenza viruses include many different subtypes, classified according to the nature of the two components that make up the virus – haemagglutinin (H) and neuraminidase (N) – proteins found on the surface of influenza viruses. There are 18 haemagglutinin and 11 neuraminidase subtypes of influenza A virus, giving rise to hundreds of variations on the ‘HxNy’ combination. Avian influenza strains that do not cause significant disease signs in poultry are considered low pathogenic while those leading to severe disease (including severe respiratory syndrome, and nervous signs) and high mortality rates are called highly pathogenic (WHO, 2018). Since the emergence of the H5N1 Highly Pathogenic Avian Influenza (HPAI) virus subtype in 1997 in Asia, several other subtypes have appeared due to the constant evolution and diversification of avian influenza viruses and progressively spread across continents (OIE, 2016; CDC, 2017).

Metrics and numeric limits

Avian influenza viruses of the H5 and H7 subtypes, as well as any influenza A virus with high pathogenicity are notifiable to the World Organisation for Animal Health (OIE) under the Terrestrial Animal Health Code. An intravenous pathogenicity index (IVPI) greater than 1.2 (or as an alternative at least 75% mortality) in chickens determines the strain to be HPAI (OIE, 2017, 2019).

Examples of drivers, outcomes and risk management

Drivers: Introduction of an avian influenza virus to a susceptible flock via poultry trade-related activities or farming and sale (live bird markets), or wild birds and migratory routes (OIE, no date b).

Outcomes: High mortality in poultry with sudden death of birds, may cause severe illness in humans, stamping-out of birds in the affected flock or farm, poultry movement restrictions, trade ban, livelihoods, food security and health implications, in particular women and children who often are the ones caring for poultry (OIE, no date b).

Risk management: Farm and market biosecurity improvement, movement control, depopulation, tracing back/forward, vaccination (prevention, only if the country allows vaccination of birds against avian influenza), compartmentalisation, food hygiene (OIE, no date b).