Britain gassed tens of thousands of turkeys and extended restrictions on the movement of poultry yesterday to try to prevent the spread of deadly bird flu from a farm in eastern England.

The discovery of the highly pathogenic H5N1 strain of avian flu on a farm run by Europe's largest turkey producer surprised experts and raised questions about how the virus had been introduced into a sealed shed.

However, the Department for the Environment, Food and Rural Affairs (DEFRA) expressed optimism that the virus had been confined to the Bernard Matthews farm near Lowestoft in the county of Suffolk.

"Obviously, though, we need to be very vigilant in the coming days," a spokeswoman said.

The slaughter of 159,000 birds at the farm, which started late on Saturday, was expected to take another two days. The dead birds were being transported from the farm in sealed trucks to be incinerated.

About 2,500 turkeys died in the initial outbreak of the virus, which appears to have been confined to one of 22 sheds at the farm.

Restrictions on the movement of poultry were extended overnight to a 2,000-sq-km area around the farm.

The strain has killed at least 165 people worldwide since 2003, most of them in Asia, and more than 200 million birds have died from it, or been killed to prevent its spread.

However, it has not yet fulfilled scientists' worst fears by mutating into a form that could be easily transmitted between humans and possibly cause a global pandemic.

But in Jakarta, the UN official coordinating the global fight against the virus warned yesterday the world should expect more bird flu outbreaks in the coming months.

Dr David Nabarro said countries where the virus was not endemic would likely see more cases in poultry in the first half of this year, mostly spread by migrating birds.

"I am expecting to see outbreaks of highly pathogenic avian influenza in a number of locations over the next three or four months, and I am basing it on what happened last year," he said, stressing that the risk to human health remained very small.

Nabarro said a recent spike in human deaths in Indonesia meant the country must do more to fight the virus despite improving its efforts in recent months, including the cull of backyard chickens in the capital last week.

In Geneva, the World Health Organization (WHO) confirmed on Saturday that bird flu killed a 22-year-old Nigerian woman, making her the first known human fatality of the H5N1 virus in sub-Saharan Africa.

"The WHO's collaborating centre has confirmed that it is H5N1," said Gregory Hartl, a spokesman for the United Nations' health agency.

Source: China Daily/Agencies