"This could either be caused by some changes within the virus itself or some other factors, probably the illegal use of vaccine in poultry," said caretaker Public Health Minister Pinij Charusom-bat.

This year, two confirmed bird-flu patients who have already succumbed to the disease. Initial lab tests showed they did not have the virus.

"They had the symptoms, yet both the rapid test and PCR (Polymerase Chain Reaction) showed negative results," he said.

Pinij insisted the virus was still H5N1, but he and his team observed that something irregular might have happened in those cases.

The illegal use of vaccine could be to blame, he said, adding they had discovered there was a type of vaccine produced based on the H5N2 strain, which could have something to do with the observed changes of the H5N1 virus in some human cases.

The ministry's Medical Sciences and Medical Services departments together will be monitoring and studying to find out more, the minister said.

The ministry's concerns over possible changes in the virus suggested some changes in screening and treating patients with bird-flu like symptoms, Pinij said.

 "From now on, doctors should not base their decisions to give Tamiflu on the lab results as much as they did before," he said, adding that if any patient showed suspected symptoms and had a history of having been in contact with sick or dead poultry, then the doctor could consider giving the anti-viral drug to the patient.

These recommendations were based on the experts' conclusion on Monday when they met at the ministry to review current situations concerning screening and treatment of patients with suspected symptoms.

 However, Pinij said, the decision to give the drug or not should be carried out on a case-by-case basis to prevent too much use which could lead to resistance.

Yesterday, the Public Health Ministry called an urgent meeting of health officials from 29 provinces listed as areas to be closely monitored for bird flu epidemics in poultry and other concerned parties including the Ministry of Agriculture and Co-operatives.

Dismissing the caretaker Agriculture and Co-operatives Minister Khunying Sudarat Keyuraphan's concerns, Pinij said he insisted the recent two confirmed cases of bird flu this year did contract the virus from poultry - and not other sources as speculated.

Sudarat said on Monday that since the avian flu virus had not been detected in Uthai Thani, Public Health officials needed to find out why and how the Uthai Thani patient had the virus.

Dr Charal Trinvudhipong, Sudarat's assistant, said that in the Uthai Thani case, the dead chickens were not tested because they had been buried already and the negative results came from a different batch of live chickens.

The meeting also agreed to involve scientists studying the adverse effects of bird-flu vaccine on the accuracy of testing bird flu in human cases - as well as the genetics of the virus, Charal said.

The outcome of the study should shed light on what the Public Health Ministry suspected about the virus, he said.

The team will comprise virus and animal disease experts from Chulalongkorn, Kasetsart, and Mahidol Universities.

Fighting cocks and ornamental birds are the most worrying group concerning the risk of illegal use of bird flu vaccine, Charal said, adding it had been discovered that about 50 per cent of the free-range ducks had antibodies to the bird flu virus.

Meanwhile Suphan Buri Governor Songpol Timasart has ordered all cockfights in the province banned until the virus is fully under control.

"Failure to abide by the ban will result in immediate legal action," Suphan Buri Deputy Governor Somsak Pureesrisak said yesterday.

In Bangkok, four patients including a three-year-old boy were listed for bird flu observation yesterday.

Arthit Khwankhom

 The Nation