Avian Influenza (or bird flu) is a contagious viral infection that can affect wild and domestic birds and manifest itself in different ways depending on the pathogenic character of the virus involved and on the bird species affected. This virus has been detected particularly in waterfowl (ducks, geese and swans) but also in other species, including gulls and birds of prey.
AI is widespread in populations of wild birds, but typically has low lethality (so-called Low Pathogenic Avian Influenza - LPAI). However, there is concern about the fact that the Asian strain of a highly virulent form of this virus (Highly Pathogenic Avian Influenza - HPAI - subtype H5N1 “Asian strain”) has been recorded in wild birds in several countries in Asia, the Middle East and Europe. There are further concerns that wild birds in Africa may also be affected, even if so far only very few cases have been confirmed there.

AI can result in significant mortality in wild bird populations. This situation is potentially most serious for species with low population levels that congregate in a small number of sites. For example in the spring of 2005 it was estimated that between 5% and 10% of the world population of Bar-headed Geese Anser indicus died in the outbreak at Lake Qinghai, in China.

Spread of AI

There are a number of potential ways by which H5N1 can be spread within and between countries. These include the movement of poultry (and poultry products), of caged birds for trade and of migratory birds. The pattern of outbreaks of H5N1 in the EU and in some other European countries, as well as scientific publications on HPAI H5N1 in Asia, suggest that migratory birds are capable of transmitting the virus over long distances.

H5N1 is considered to have originated in South-east Asia, where it was first detected in 1997. It first spread to Kazakhstan and southern Russia in the summer of 2005 and was recorded in Turkey, Romania, Croatia and western Russia in autumn of that year. As a result, several additional surveillance, prevention and control measures were taken by the European Commission and the EU Member States, on the assumption that the disease would soon enter the EU.

However, the scientific evidence suggested initially that there would be a relatively low risk of an outbreak of H5N1 in the European Union in the winter 2005/2006, with the possible exception of some areas along the Mediterranean (Greece, in particular). Most cases were indeed recorded along a south-eastern migration flyway, taking birds mainly through the middle-east into Africa. It was expected that the EU would be at higher risk in spring, when birds migrate northwards to the EU from Africa after possibly being in contact with infected birds of Asian origin on the African wintering grounds.
The outbreaks that took place from mid-February in the EU were therefore not entirely anticipated. Many of these outbreaks have involved Mute Swans (over 60%), probably resulting from cold weather dispersal of birds.

Current situation

In the European Union, at present (April 2008) 11 cases of wild birds infected with HPAI H5 subtype have been recorded - see overview tables.