Avian influenza is largely a disease of birds. Despite large outbreaks in poultry, only about 140 people have so far caught the disease. Of these, about half have died. All human cases have occurred in Vietnam, Thailand, Cambodia, Indonesia, China and Turkey. Almost all are thought to have caught the disease from infected poultry. There has been no sustained human-to-human transmission: the virus does not pass easily between people.

Medical experts warn that the avian influenza virus could combine with influenza viruses already circulating in the human population or adapt into a form which could be transmitted readily between people. It is impossible to predict when this might happen. But if it did, it could trigger a global human flu pandemic.

It is important to distinguish between avian flu, the current disease affecting mainly birds, and pandemic flu, which would affect mainly humans and is at this stage only a possibility.