Highly pathogenic Avian Influenza (HPAI) is a highly contagious disease of domestic fowl caused by a virus commonly found in water birds. The latter are usually not affected by the disease and serve as the entry point of infection into domestic poultry.

Many of the strains that circulate in wild birds are either non-pathogenic or low pathogenic for poultry. However, a virulent strain may emerge either by genetic mutation or by reassortment of less virulent strains.

Once introduced into domestic flocks, wild birds are probably not essential for maintenance of an outbreak which spreads through other methods, involving movement of infected poultry, contaminated equipment, vehicles, personnel and other means.

Due to its close relationship with wild birds, HPAI strains can emerge and cause disease in domestic poultry in any country at any time without warning as has been shown with outbreaks occurring at irregular intervals on all continents.

AI viruses are probably ubiquitous in wild waterbirds. Pathogenic strains could emerge and cause disease in domestic poultry in any country at any time without warning. In fact, outbreaks have occurred at irregular intervals on all continents.

Click to open the dynamic map of the Geographical Distribution

Serious epidemics have occurred in Italy 1997, Hong Kong 1997-1998 and 2003, Chile 2002 and The Netherlands 2003. In addition, following the outbreak in Hong Kong where 18 people were infected and six people died of an avian flu strain, directly contracted from infected birds, the role of the avian species in the epidemiology of human influenza had to be reconsidered as well as the importance of the disease as a public health issue.

The magnitude of the 2004 epidemic in Asia highlights HPAI as a major epidemic transboundary disease with the potential to generate a great deal of concern because of the economic, trade and social repercussions.

It has become an international problem that affects animal health, human health, food security, economies and the society in general. It has threatened the livelihood of millions of people depending on poultry for their subsistence; the number of poultry lost was estimated to be more than 100 million. Human infections and deaths caused by H5N1 have been reported in Viet Nam and Thailand, which has also reported the disease and deaths in other non-avian species e.g. cats. More than half of the affected countries experienced HPAI for the first time in their histories.