Bird flu (also called avian influenza, avian flu, bird influenza, or grippe of the birds), is an illness caused by a virus. The virus, called influenza A or type A, usually lives in birds, but sometimes infects mammals, including humans. It is called influenza when it infects humans.
But some types kill birds, and a few kill humans and other mammals. One type of bird flu, called Spanish flu, killed 50 to 100 million people in 1918/1920. Another type, called Asian Flu killed one million in 1957, and another one, called Hong Kong Flu, also killed one million people in 1968.
A subtype, called H5N1, killed six people in Hong Kong in 1997, but did not kill again until 2003, this time in China. Until the middle of 2005, it was primarily found in southeast Asia but since then has spread to parts of Africa and Europe. It has killed tens of millions of birds and resulted in the slaughter of hundreds of millions of other birds to limit its spread. So far it is mostly a bird disease and rarely infects humans. The concern about H5N1 is that it is constantly evolving at a very fast rate and could create a human flu pandemic that could kill many millions of people. Governments around the world are spending billions of dollars to deal with this problem: studying H5N1, creating vaccines, conducting pandemic practice exercises, stockpiling useful flu medication, and many other important activities.