With the worldwide death toll from bird flu set to pass 100, scientists yesterday called for renewed vigilance against the virus which is rapidly spreading across the world.

Three suspected bird flu fatalities reported in Central Asia's Azerbaijan would, if confirmed by the World Health Organization (WHO), bring the number of H5N1 deaths to 101 since the current outbreak erupted in East Asia in late 2003.

Scientists fear the virus will mutate into a form that transmits easily between humans and cause a pandemic that could kill millions.

Azerbaijan's suspected cases add to a lengthening list of nations hit by the disease. More than 35 countries have reported outbreaks amongst birds, and Azerbaijan would be the eighth to record human deaths.

The spread of the highly pathogenic virus has accelerated in the past 12 months, with various strains extending deep into Eastern, then Western Europe, parts of the Middle East and now into Africa and the Indian Subcontinent.

As scientists find more and more evidence to support the theory that the disease is being transmitted by migratory wild birds, the list of affected countries is expected to keep on growing.

"Every single human infection that is reported is a cause for concern and the threat of a bird flu pandemic grows from month to month," said WHO Asia-Pacific spokesman Peter Cordingley, who added that the UN body had yet to verify Azerbaijan's positive tests on the three fatalities.

But while the rapid expansion is fuelling fears that the chance of H5N1 mutating into a more contagious form, scientists say little has changed so far.

"The virus has changed that's what viruses do for a living, but there is no evidence to show that it has mutated into a form that could cause a pandemic in humans," Cordingley said.

The WHO's official tally of confirmed human cases runs from late 2003 and currently stands at 177 cases, 98 of them fatal.

The worst-hit country is Viet Nam where 42 people have died as a result of the disease, spread mostly through contact with infected birds.

Although no human cases have been found in Western Europe, the virus has emerged there in recent months with Cyprus, France, Austria, Germany and Greece all reporting isolated outbreaks.

With a mortality rate in excess of 50 per cent, the H5N1 strain is more deadly than even the 1918 so-called Spanish Flu pandemic, estimated to have killed 20-40 million people worldwide.

Although a handful of infections are suspected to have occurred from close contact with infected humans, scientists do not believe the disease's genetic make-up has altered to the point that it could explode into a full-blown pandemic.

"To become a pandemic the virus has to go through a number of mutation barriers and from what we have found, we are no nearer to that," said Frederick Leung, dean of science at Hong Kong University.

Source: China Daily