Avian influenza is not new. There are many strains of the virus that have probably been carried in the intestines of birds for thousands of years. Most of the time, these viruses cause few, if any symptoms in wild birds and also pose no threat to people. However, some strains are “highly pathogenic,” causing severe symptoms and death in birds, especially poultry.

The severe form of avian flu caused by the highly pathogenic H5N1 virus was first isolated from a domestic goose in Guangdong, China, in 1996. In most cases so far, the wild birds appear to have contracted the avian flu virus from poultry. Waterfowl and shorebirds are more prone to get the disease than other species. The virus has been found in a variety of wild birds in Europe and the Near East, including Mute Swans, Bar-headed Geese, Tufted Ducks, several birds of prey, and House Sparrows. In some cases, birds may be resistant to the virus and not show any symptoms, but still be a carrier as in some wild ducks.

It is possible, but not highly likely, that this new highly pathogenic strain of avian flu could get into the United States first via migratory birds. Infected wild birds from Asia would have to survive the disease and carry it to breeding grounds in the Pacific Islands or Alaska. The virus would then have to pass to another species that migrates to the lower 48 states. That bird would also have to survive the virus. Only then might it be spread to other birds in the continental United States. Ninety-nine percent of North American migrants do not come from Europe or Asia where the virus has been found. This year scientists will test about 100,000 birds in Alaska, Canada, and along major flyways in the United States in an effort to detect whether avian flu has arrived via these routes.

For more information on avian influenza and wild birds, visit the following web sites:

• A USDA fact sheet on the government's plan to screen wild birds for the H5N1 virus.

• An international view on the spread of avian influenza in wild birds and the impact on conservation, BirdLife International.
  

• A chart listing species affected by the avian flu virus to date, from the United States Geological Survey.
  

• Where to report sick or dead wild birds, U.S. Department of Agriculture.
  

Please visit our Q&A section for answers to other questions about how wild birds are affected by the avian flu.

• Is it safe to watch birds, feed birds, and monitor nest boxes?
• Should wild birds be culled?
• What are avian influenza viruses and how do they mutate?