The human death toll from bird flu has now passed 100, following the confirmation of five new fatal cases in Azerbaijan, possibly as a result of collecting feathers from dead swans, the United Nations health agency reported.

Last week, the World Health Organization strengthened its field team in Azerbaijan to include experts in clinical management and infection control and additional senior epidemiologists to fight the H5N1 virus, which experts fear could mutate into a potentially devastating and lethal human pandemic.

As of today there have been 184 human cases, 103 of them fatal, in the two-year-old outbreak, with almost all infections caused by very close contact with sick or dead birds.

At present, WHO said, bird flu remains an animal pandemic that very rarely infects humans, and that there is no sign that the virus is changing in order to spread more easily from animal to human or from human to human. It stressed that detection of the virus in new regions does not mean that a human pandemic has started.

Over the weekend, a field investigation conducted jointly by WHO and the Azeri Ministry of Health found evidence that carcasses of numerous swans, dead for some weeks but not buried, may have been collected by residents as a source of feathers.

De-feathering of birds is a task usually undertaken by adolescent girls and young women. The WHO team is today investigating whether this practice may have been the source of infection in a village where the majority of cases have occurred in females between the ages of 15 and 20.

The great concern is that the virus could mutate into a type that spreads easily from person to person. The so-called Spanish flu pandemic that broke out in 1918 is estimated to have killed from 20 million to 40 million people worldwide by the time it had run its course two years later.