“VIRUS DISEASES” OF ANIMALS

as pet birds and wild birds with some strains resulting in high mortality rates. The virus has also been isolated from mammalian species including humans, rats and mice, weasels and ferrets, pigs, cats, tigers and dogs. AI viruses are not new. There are many descriptions of historical outbreaks of AI in domestic poultry throughout available literature. There are many strains of AI viruses and generally they can be classified into two categories: low pathogenic (LPAI) that typically causes little or no clinical signs in birds and highly pathogenic (HPAI) that can cause severe clinical signs and/or high mortality in birds. The Asian origin highly pathogenic H5N1 strain of the AI virus has attracted much attention over the last few years because of significant outbreaks globally in domestic and wild birds. Concern is raised because of the degree of virulence not only in poultry but also in wild birds as well as the ability to infect mammalian species. While AI viruses are generally highly species specific, the highly pathogenic H5N1 AI virus has also infected humans. Low pathogenic strains of AI H5N1 virus exist but do not produce significant clinical signs in birds. • In 1997, a highly pathogenic strain of H5N1 AI emerged in Southeast Asia and spread throughout numerous Asian, Middle Eastern, African, and European countries. It has also been associated with illness and death in humans who have had close contact with infected birds. • In 2002, mortalities in wild birds due to highly pathogenic avian influenza (HPAI) were reported in Hong Kong. These were the first reported deaths of wild birds as a result of HPAI in Asia. • The first AI H5N1 case reported in Africa was in February 2006 in Nigeria. • Outbreaks of highly pathogenic H5N1 AI in domestic birds occurring in Asia, Africa and Europe mark the first time in the history of this disease where so many countries have been simultaneously affected with the loss of so many birds.