Avian influenza is an infectious disease of viral etiology that ranges from a mild or even asymptomatic infection to an acute, fatal disease of chickens, turkeys, ducks, quails, pheasants, guinea fowls, and other avian species.

Influenza virus Type A is the causative agent. This virus can infect several animal species - pigs, horses, monkeys, seals and whales. Normally avian influenza viruses do not directly infect humans or circulate among humans. Wild birds, especially migratory waterfowls are the natural reservoirs of Type A influenza virus. With the start of migratory season, bar headed geese, large cormorants and black-headed gulls are the main suspects to be watched out.

Avian influenza virus generally causes mild / no symptoms in birds. However, the range of symptoms in birds varies greatly depending on the strain of virus and the type of bird. Infection with certain avian influenza A viruses - for example, some H5 and H7 strains can cause widespread disease and death among some species of wild and especially domesticated birds such as chickens and turkeys.

Etiology

Avian Influenza virus belongs to Family Orthomyxoviridae and Genus Influenzavirus Type A. Influenza A viruses can be divided into two subtypes on the basis of their surface proteins — hemagglutinin (HA) and neuraminidase (NA) sub types. There are 16 known H subtypes and 9 N subtypes. From 1997 onwards all highly pathogenic isolates have been of influenza A viruses of subtypes H5 and H7.

AI viruses can be classified into low pathogenic (LPAI) and highly pathogenic (HPAI) forms based on the severity of the illness they cause. Many of the strains that circulate in wild birds are either non-pathogenic or midly pathogenic for poultry. However, a virulent strain may emerge either by genetic mutation or by reassortment of less virulent strains. The avian H5N1 strain is a highly pathogenic strain with pandemic potential.

Properties of the Virus

Temperature     : Inactivation by 56°C/3 hours; 60°C/30 min

pH                    : Inactivated by acid pH

Chemicals         : Inactivated by oxidising agents, sodium dodecyl sulphate, lipid solvents,  

                           ß-propiolactone

Disinfectants      : Inactivated by formalin and iodine compounds

Survival             : Remains viable for long periods in tissues, faeces and also in water

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