Classification: ICD-9 488.01; ICD-10 J09.0
Synonyms: Bird flu, avian influenza, highly pathogenic avian influenza, H5N1.
Agent: Influenza A subtype H5N1, a RNA virus, family Orthomyxoviridae. Avian influenza H5N1 occurs in two forms, a virulent form known as highly pathogenic avian influenza H5N1 (HPAI H5N1) and a milder form known as ‘low pathogenic’ (LPAI H5N1). H5N1 viruses have diverged into geographically distinct strains (genetic clades).
Reservoir: LPAI viruses naturally circulate in wild birds, principally waterfowl and gulls, in which they generally cause no symptoms. LPAI viruses are transmitted to terrestrial poultry (chickens, turkeys). LPAI most likely evolved to HPAI in aquatic birds (ducks and geese). Transmission of HPAI into migratory birds can result in large die-offs.
Transmission: Direct contact with sick or dead poultry (most common) infected with HPAI, and possibly via inhalation of virus-laden particles or contact of contaminated material with the eyes or respiratory mucosa. Other postulated routes: ingestion of water contaminated with the feces of infected birds, consumption of undercooked products from infected birds. Often, however, the route of exposure is not clear. Limited person-to-person transmission of HPAI H5N1 is possible following prolonged close contact with an infected patient.
Incubation period: 3 days (range 2–9 days).
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