Highly pathogenic avian influenza

Highly pathogenic (HP) avian influenza (Al) (HPAI) is an extremely contagio us, multi-organ systemic disease of poultry leading to high mortality, and caused by some H5 and H7 subtypes of type A influenza virus, family Orthomy xoviridae. However, most Al virus strains are mildly pathogenic (MP) and pr oduce either subclinical infections or respiratory and/or reproductive dise ases in a variety of domestic and wild bird species. Highly pathogenic avia n influenza is a List A disease of the Office International des Epizooties, while MPAI is neither a List A nor List B disease. Eighteen outbreaks of H PAI have been documented since the identification of Al virus as the cause of fowl plague in 1955. Mildly pathogenic avian influenza viruses are maintained in wild aquatic bi rd reservoirs, occasionally crossing over to domestic poultry and causing o utbreaks of mild disease. Highly pathogenic avian influenza viruses do not have a recognised wild bird reservoir, but can occasionally be isolated fro m wild birds during outbreaks in domestic poultry, Highly pathogenic avian influenza viruses have been documented to arise from MPAI viruses through m utations in the haemagglutinin surface protein. Prevention of exposure to the virus and eradication are the accepted method s for dealing with HPAI. Control programmes, which imply allowing a low inc idence of infection, are not an acceptable method for managing HPAI, but ha ve been used during some outbreaks of MPAI. The components of a strategy to deal with MPAI or HPAI include surveillance and diagnosis, biosecurity, ed ucation, quarantine and depopulation, Vaccination has been used in some con trol and eradication programmes for Al.