What is bird flu (avian influenza A H5N1)?
Bird flu, also called avian influenza A, is a viral infection that occurs in birds. It is carried by wild birds. It can also infect domestic birds, such as chickens, ducks, and turkeys. When it infects birds, it makes them sick and sometimes kills them. There are many strains of influenza. The type of bird flu that is very deadly is called influenza A H5N1. Viruses often change (mutate). They may then spread more easily among animals and humans. They can also become more deadly. The strain of influenza that is now common in birds in Asia could change into a flu that spreads more easily to humans. National and world health organizations worry that a mutated bird flu virus could cause a world-wide epidemic (pandemic). Many people have at least some immunity to human viruses, which means their body can more easily fight the virus. A pandemic flu happens when there are worldwide epidemics of flu caused by a new flu virus to which people have little or no immunity.
