Virus's rapid march around the globe

Bird flu has been reported in 14 more countries in February, marking a sudden resurgence of the H5N1 influenza virus, which scientists fear could trigger a pandemic if it mutates and jumps from person to person.

Many of the outbreaks have involved wild birds and the World Health Organisation says migratory fowl are believed to be one way the virus is spreading.

In a report on its website (www.who.int), the WHO said the H5N1 virus has been undergoing steady genetic mutations that have affected patterns of virus transmission and spread among domestic and wild birds. They have not, however, had any discernible impact on the disease in humans. Infections in people remain rare.

Studies have shown that different H5N1 strains have become progressively more lethal in birds and are also hardier, surviving several days longer in the environment, the WHO says.

Domestic ducks have acquired an ability to resist the disease caused by some strains, and are now capable of excreting large quantities of highly pathogenic virus without showing the warning signs of illness.

Following are the countries that have reported outbreaks this month: Austria, Azerbaijan, Bosnia and Herzegovina, Bulgaria, Egypt, France, Germany, Greece, Hungary, India, Iran, Italy, Malaysia, Nigeria and Slovenia.

In total, bird flu has been detected in more than 30 countries and territories since 2003, when it flared anew.

It made the first jump into humans in Hong Kong in 1997, killing six people and prompting the government to cull its entire stock of poultry.

Since 2003, a total of 170 people are known to have been infected by the virus, killing 92 of them, according to the WHO.