Britain is to slaughter 35,000 chickens after bird flu was found among dead birds on a farm in one of the country’s biggest poultry farming areas, the government said on Wednesday.

A Department for Environment, Food and Rural Affairs (DEFRA) spokesman said the cull of all the birds on the farm in eastern England would take place as a precautionary measure.

“The preliminary test results show that it is likely to be the H7 strain of avian influenza and not H5N1,” DEFRA said in a statement. The feared H5N1 strain has killed more than 100 people since late 2003, most of them in Asia.

The outbreak is on a farm near the market town of Dereham, in the eastern county of Norfolk, an agricultural center that is home to some of Europe’s biggest poultry farms.

An outbreak of the H7N7 bird flu strain in the Netherlands in 2003 led to the culling of 30 million birds, about a third of all Dutch poultry at a cost of hundreds of millions of euros.

A veterinarian working on an infected Dutch farm caught the disease and later died of pneumonia. It infected more than 80 people in total.

“Further tests are being carried out to determine the strain of the virus and more will be known tomorrow (Thursday),” the government said in a statement. “As a precautionary measure, birds on the premises will be slaughtered.”

Earlier this month, Britain confirmed its first case of H5N1 bird flu in a wild bird when a dead swan was found in eastern Scotland.

The swan was the only wild bird so far found in Britain to have the H5N1 virus, which has led to the death and culling of 200 million birds since around the world since late 2003.

Scientists fear bird flu could become highly dangerous to humans if the virus mutates into a form easily passed on from one person to another.

Both highly pathogenic and low pathogenic avian influenzas can infect humans but rarely do so. H5N1 is the bird flu strain that poses the biggest threat to public health, although cases of human infection remain relatively infrequent.