Migatory birds study in search for flu vaccine

Speaking at the three-day Avian Influenza 2008 conference at the Dusit Thani Hotel in Bangkok, which started yesterday, Professor Robert G Webster said the results of the study will be key in developing a bird-flu vaccine.

"We have to answer questions such as what are the ultimate reservoirs of the highly pathogenic H5N1 virus? Why have the viruses not spread to the Americas and Australia? What are the molecular requirements that will permit H5N1 to acquire consistent transmissibility in humans? These are question that we have to address as the virus continues to evolve," he said.

Pandemic influenza is caused by the transfer of influenza A virus or virus gene segments from aquatic birds to humans and domestic animals.

Wild aquatic birds are the natural host of influenza viruses. These viruses exist in harmony with their hosts and are non-pathogenic, but after transfer to other species, they evolve rapidly. In the past century, there have been three pandemics in humans: Spanish flu in 1918, Asian flu in 1957, and Hong Kong flu in 1968. These have emerged by mutating between human influenza viruses and those carried by aquatic birds or directly from other avian sources. It is now a decade since H5N1 emerged in Asia and the virus continues to spread and to increase its host range and genetic and antigenic diversity.

"The probability is that we are witnessing in real-time the evolution of pandemic strain and the virus is continuing to evolve," Webster said.

The remarkable genetic diversity of the H5N1 virus may have occurred because it moved successfully between multiple species of birds and mammals.

"The original virus, which emerged from an unknown source in the natural wild-bird reservoir, became highly pathogenic and established among the domestic waterfowl in Asia," he said.

From 1997-2004, H5N1 was largely confined to Southeast Asian countries with high death rates in domestic poultry and transmissions to humans, from which over 60 per cent of those infected had died.

In May 2005, H5N1 infected Bar-headed geese and other waterfowl on Qinghai Lake, China, killing a high percentage of infected birds. Subsequently the virus spread rapidly to India, Africa and European regions near Asia.

Pongphon Sarnsamak

The Nation