Abstract
Influenza virus is an RNA virus that exists as different types and subtypes. Influenza A virus strains are known to cause disease in several bird and mammalian species. Wild birds are believed to constitute the natural reservoir for influenza A virus. Influenza A virus has the ability to change through antigenic drift and recombination allowing for the emergence of new strains and subtype combinations. In man influenza A virus causes yearly seasonal epidemics and, at irregular intervals, pandemic outbreaks have had a devastating impact on mankind. For example, the Spanish influenza pandemic of 1918 is thought to have killed more than 50 million people. Influenza A virus is an important cause of disease in poultry, where virus strains of the H5 and H7 subtypes may change into forms that are highly pathogenic. These virus strains may transmit directly to man and multiple other species. This has been the case in the ongoing outbreak that started in South-east Asia in 2003. All known subtypes of influenza A virus have been isolated from wild birds living in aquatic environments, mainly dabbling ducks. This review focuses on what is known about the pathogenicity and spread of influenza A virus in species other than man, with particular emphasis on the wild bird reservoir.