Avian influenza: A pandemic threat

Avian influenza is a highly contagious viral disease of poultry caused by enveloped Influenza A RNA viruses of Orthomyxoviridae family. The highly pathogenic H5N1 virus which was first isolated from a domestic goose in China in 1996 was responsible for the first mortality in the human. Viruses that cause severe disease in birds and result in high mortality rate are called highly pathogenic avian influenza (HPAI), whereas viruses that cause outbreaks in poultry but are not generally associated with severe disease are called low pathogenic avian influenza virus (LPAI). Till date, naturally occurring HPAI have been associated with H5 and H7 subtypes. Genetic reassortment between human and avian viruses is suggestive as the mechanism by which ‘‘new’’ human pandemic strains arise. The disease begins by inhalation or ingestion of LPAI or HPAI viruses in the nasal cavity, which is the major site of initial replication. Good husbandry measures, healthy diet and broad spectrum antibiotics to control secondary bacterial infections may reduce the mortality rate.