May 27, 2005 (CIDRAP News) – Avian influenza could be infecting up to half of the pig population in some areas of Indonesia, but without causing symptoms, Nature magazine reported in this week"e;s edition.

Meanwhile, Chinese officials said a flu outbreak among wild birds is twice as large as previously reported, but they denied reports of human cases.

In Indonesia, Chairul Nidom, a virologist at Airlangga University"e;s tropical disease center in Surabaya, Java, was conducting independent research earlier this year. He tested the blood of 10 apparently healthy pigs housed near poultry farms in western Java where avian flu had broken out, Nature reported. Five of the pig samples contained the H5N1 virus.

The Indonesian government has since found similar results in the same region, Nature reported. Additional tests of 150 pigs outside the area were negative. However, the story said, lack of funding for surveillance and testing is a concern to Nidom, who said he has samples from 90 more pigs from Banten, but he can"e;t afford to test them or to broaden his investigation.

"I think pigs pose a much greater threat of spreading the disease to humans than poultry," Nidom told Nature. Pigs are often described as a mixing vessel in which human and avian flu viruses can swap genetic information, which could lead to a hybrid virus with the ability to spread easily among people.

The Indonesian government sent a report to the World Organization for Animal Health (OIE) on May 23 that describes three surveys involving "purposive and pooled sampling" of pigs, with a total 187 samples.

The first survey, Nidom"e;s Feb 23 study on one farm, yielded 5 positives out of 10 samples tested for H5N1. The second, on Apr 14 in another village, involved 10 nasal swabs from 31 pigs and produced positives in 6 of the 10.

The third survey included six pigs from the same village as Nidom"e;s small survey and yielded 1 positive swab. The report says that no pig has shown visible signs of avian flu. It lists the source of the pig infections as "contamination with chicken manure" from adjacent backyard chicken farms.

Additional tests included 250 blood serum and swab samples from pigs in seven provinces, the report says. All the results were negative.

The Nature report said the H5N1 virus was found in pigs in China in 2001 and 2003, but two surveys last year, involving 8,457 pig samples, found no evidence of the virus.

In China, more than 1,000 migratory birds have died of H5N1 avian flu in Qinghai province, according to a report today by Xinhua, the Chinese news agency.

The size of the outbreak, initially reported as not being H5N1, grew this week from 178 birds to 519, and now to more than 1,000. Emergency measures are being taken in Qinghai, including increasing infectious disease control and surveillance for animals and humans, Xinhua reports. The agency said earlier that authorities planned to vaccinate 3 million poultry in the region.

The Chinese government has repeatedly said that no people have been infected with avian flu, despite unconfirmed claims on Internet sites that as many as 120 people have died of the illness.

The World Health Organization (WHO) is seeking details on the provincial outbreak, according to a Canadian Press (CP) report quoting Maria Cheng, WHO spokeswoman in Beijing.

"We"e;ve seen those reports about possible human H5N1 cases, and have requested more information from the Ministry of Health," Cheng said. The WHO is urging China to share virus samples from the dead birds as well as information on human exposure to dead birds.

"It would be premature to consider this event over," Cheng said.

In a separate report in Xinhua yesterday, Chinese researchers claimed to have developed two H5N1 vaccines that are "100%" effective for birds, animals, and people, CP reported. Officials at the WHO office in Beijing, however, described that research as involving only birds and said no animal or human clinical trials have been conducted.