Avian Influenza: Influenza caused by viruses adapted to birds

The virus, called influenza A or type A, usually lives in birds. Sometimes it infects mammals, including humans.

There are many types of influenza A, which was first found in a bird in Italy in 1878. Most types have weak symptoms, such as breathing problems, similar to the common cold.

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. It might create a human flu pandemic. Governments around the world are spending money to deal with this problem: studying H5N1, creating vaccines, conducting pandemic practice exercises, stockpiling useful flu medication, and many other activities.