How does bird flu affect humans?
The H5N1 strain of bird flu virus has caused outbreaks of illness in poultry flocks throughout the world from time to time over the last 40 years or so. It was not thought to be a threat to humans as bird flu viruses generally do not affect humans. However, in 1997 an outbreak of bird flu in Hong Kong with the H5N1 strain infected 18 people, and six died of the infection. This is of great concern because it showed that the H5N1 strain had mutated in some way to be able to infect humans as well as birds. And also, it caused a very serious illness. These human cases were in people who had been in close contact with infected birds and had caught the illness directly from the birds. The infected people did not pass on the infection to other people. Since 1997 there have been several more outbreaks of H5N1 bird flu in several countries. In some of these outbreaks, millions of poultry birds have died from the disease or were killed (culled by the authorities) in order to try to control the o
