However, fears of a new pandemic, which could claim millions of lives, have not been realised so far, even though the mortality rate of the disease among humans has risen above 60%.

Experts point out that cross-infection to humans is still relatively rare and usually occurs where people have been in close contact with infected birds.

But international bodies, such as the World Health Organization and the UN's Food and Agriculture Organization, have been using their knowledge and experience of outbreaks to prepare for a possible pandemic.

The big fear remains the risk of the H5N1 bird-flu strain combining with a human strain to produce a mutation that is more dangerous and difficult to combat.

This map will generally be updated at six-monthly intervals