Population | Economy | Travel | Birds

Migration

The spread of the H5N1 flu strain originating in Southeast Asia was initially attributed to annual bird migrations that crossed Europe into Africa. Wild birds are able to convey the viruses to domestic poultry flocks without contracting severe disease themselves and outbreaks were expected to appear along their migratory routes. However, this theory did not entirely sustain, with the virus spreading only so far as Russia and Turkey but stopping short at Nigeria in Northern Africa as the migration season of 2005 ended. Several European countries along Western Europe, including Germany and Switzerland, had already evaluated the risks of bird migrations quite heavily and earlier implemented strict control measures against the exposure of domestic poultry to wild migratory birds. With the conclusion of the migratory season however, regulations have been loosened slightly.

Although this recent migration season did not result in the feared scenario foreseen by scientists, it could indicate that H5N1 has been principally transmitted by other means i.e. poultry import/exportations and air travel. Surveillance programs on wild bird populations in Europe showed a considerably low outbreak frequency (compared to what would be expected if wild birds were spreading the strain to the continent) and global range. Essentially, this may urge governments to focus anti bird flu campaigns on border security and quarantining.

Wild Birds

Wild birds are believed to have carried avian influenza viruses for hundreds of years without harm and are typically of little threat to wild bird populations. The viruses dwell in the intestines of bird species and only cause havoc when transmitted to domestic poultry, which have lower resistance against the virus.

However, H5N1 was earlier found responsible for the deaths of several thousand wild migratory birds near Lake Qinghai in China, a rare incident considering wild birds are believed to have higher resistance against avian flu strains. A similar scenario took place in a Mongolian reservoir, where several hundred waterfowl also fell victim to a bird flu outbreak in the wild bird population. This suggests that gradual mutations are taking place as the virus jumps from species to species - possibly even from domestic poultry back into the wild. Scattered locations of outbreaks have further led to notions that virus mutations may be producing viruses that are more adapted to infecting domestic flocks – that is, the viruses are more adapted to transmit rapidly between birds, since poultry generally live in close proximity of one another and have a short lifespan.

The likely effect of virulent bird flu viruses like H5N1 on wild bird populations however, is really impossible to determine. Wildlife monitoring programs will hopefully provide the detailed statistics in an outbreak.

Domestic Birds

Domestic poultry will generally sustain severe outbreaks as a result of their low resistance against influenza viruses. For more detail, please see Protection > Prevention > Poultry Cullings.