The finding is significant because people can no longer rely on signs of disease to tell if their flocks are infected, and they would be none the wiser if they were exposed to the virus. H5N1 infected chickens usually die within 24 hours.

?This is more dangerous. The chickens look healthy and happy but they pass the virus to us,? said Lo Wing-lok, an infectious disease expert in Hong Kong who urged China to conduct random tests on healthy looking chickens in farms and markets.

At least 97 people have died in East Asia and the Middle East since late 2003 from H5N1 and most caught it direct from infected chickens. Experts fear the virus could mutate and become more easily transmitted among people, triggering a pandemic.

But Julian Tang, a microbiologist from the Chinese University in Hong Kong, called for calm.

?Nearly all these cases (97) could be linked to symptomatically infected birds. So, looking at these figures, there seems to be very little role in transmission of H5N1 from these asymptomatically-infected birds to humans to cause a symptomatic infection,? Tang told Reuters.

The appearance of asymptomatic chickens in China, however, has raised questions about China-made vaccines.

?We?re fairly certain that what is happening in southern China is that because of the mass vaccination policy that they have been carrying out, they now have chickens that look well but which are in fact infected,? said a source familiar with the situation.

?These vaccines are not dedicated vaccines for H5N1. They don?t directly blitz the virus. They could cause mishaps?.

?We are on standby to see more (H5N1 human) cases across China ... it is not good enough just to wait for a chicken to fall over sideways and then do tests on it, you have to do pro-active tests on chickens.?

<B>Tan Ee Lyn</B>

<B>Myanmar tests show first case of bird flu </B>

Myanmar has found the H5N1 bird flu virus in chickens in what is believed to be the secretive country?s first case of the deadly disease, but there was no sign of human infection, a UNofficial said. ?The information is there is no human case so far,? said the UNofficial in Yangon, who declined to be named. The case emerged on March 8 after 112 chickens died on a farm in Aung Myae Thar Zan township near Mandalay, about 430 miles (700 km) north of Yangon. Officials destroyed a flock of 780 birds and sent samples for testing at government laboratories in Mandalay and Yangon. ?They have carried out some tests and they believe that they have identified H5N1,? Laurence Gleeson, an FAO official in Bangkok, told Reuters.

The government reported its findings on the Mandalay outbreak to the FAO and the OIE, the Paris-based international animal health body, yesterday. Dr. Tang Zhengping, the FAO representative in Yangon, said samples had also been sent to laboratories in Australia and Thailand. He said vaccines were needed to protect poultry against the disease. He did not know if foreign experts would be allowed to visit the site, but he said the military government had been cooperating with the FAO on bird flu issues.

?We have close cooperation. I am satisfied,? he said. The military-ruled country is seen by some international health experts as a potential black hole in the global fight against the disease, which has killed 97 people worldwide. While neighbouring China, Thailand and Laos have been battling a disease which swept across much of Asia in late 2003, Myanmar?s junta had insisted the country was bird-flu free.