A study has found that the bird that carried the influenza virus H5N1 into Thailand was a gull, not the openbill stork. "We have scientific evidence that a seagull was the carrier of the birdflu virus, not the openbill stork," said Professor Pilaipan Puthavathana of Mahidol University's Department of Microbiology.

Pilaipan led a team of researchers who conducted a study to track migratory routes in Asian countries by using satellite telemetry. The Thai research on human animal interface of avian influenza was supported by the US Centres for Disease Control and Prevention. It followed the migratory route of birds suspected of spreading the H5N1 virus into Thailand since 2007.

Researchers tracked the migratory route of the brownheaded gull, one of the winter visitors seen along the muddy beach at Bang Pu, Samut Prakan, every year from November to March. They started tracking the first gulls in March 2008 and a second group of seven gulls during February and March 2009. Gulls migrated out of Thailand to China in April and May. In October and November, the gulls moved south to India, Burma, and then Thailand.

Birds may stay over the winter in Thailand but some may fly further to Cambodia. Their migration can be divided into two main phases. In Phase 1, they spent November to April along the coast of the inner Gulf of Thailand; during the second phase from May to October, they wander around their breeding grounds in Qinghai, Tibet and Xinjiang in China.

The team isolated the H5N1 virus in four of 153 birds of this flock in 2005 and 2008. The flock might have played a role in the spread of H5N1 virus along its route.

The study showed that the migratory route of brownheaded gulls covered several countries that had been affected by highly pathogenic H5N1 viruses. Therefore, gulls were at risk of getting infected and spreading the influenza virus along their migratory routes. Nevertheless, it was necessary to explore whether the infected gulls were capable of migrating over long distances.

"This is the first study using satellite telemetry techniques to reveal the complete migratory routes of the brownheaded gull," Pilaipan said.

Researchers also found that the openbill stork did not migrate outside Thailand.

Previously, scientists believed the openbill stork might have migrated from other countries and spread the H5N1 virus in Thailand last year, but the recent study showed that indigenous storks had never migrated outside the country.

Pilaipan said the study would be handed to the Disease Control Department and the Department of National Parks, Wildlife and Plant Conservation so that they will collect random specimens of gulls, especially those that inhabit areas near tourist attractions, to monitor the spread of the H5N1 virus among birds and prevent its transmission to humans.