Bird flu has infected pigs in Indonesia, the Agriculture Ministry said on Friday, raising fears of a wider outbreak in the world’s fourth-most populous country and Southeast Asia’s biggest economy.

The ministry conducted tests on pigs after local scientists reported that pigs in several farms on the main island of Java were infected.

“We will continue to take some measures to prevent the avian influenza virus from spreading,” said Agriculture Minister Anton Apriyantono. “As soon as we have enough details, we will explain it further.”

So far there have been no reports of people in Indonesia being infected with the H5N1 bird flu virus. Since 2003, 36 Vietnamese, 12 Thais and four Cambodians have been killed by the H5N1 strain.

Pigs can carry human flu viruses, which can combine with the avian viruses, swap genes, and create virulent new strains, health experts say. They fear the virus could mutate into a form that can pass easily among humans and trigger a global pandemic that could kill millions.

Specimens from Indonesian poultry workers have been sent for tests in Hong Kong as a precaution, officials said.

“At the moment, the government doesn’t have an effective way to prevent the disease being transmitted from fowl to pigs. There is no vaccination yet for pigs,” said Tri Satya Putri Naipospos, director of animal health at the ministry.

New cases of H5N1 have re-emerged on a relatively small scale in some parts of Indonesia since it was first found in late 2003.

A total of 281,730 fowl either died from the virus or were culled in the January-March period, latest government data show. Since late 2003, Indonesia has lost around 8.9 million fowl.

Indonesian authorities insist that, overall, the deadly disease is under control.