The two men went missing some time after the infection was detected on the farm in Tambon Chumpol of the province's Muang district on Monday, said Kitti Puthikanont, acting head of the Disease Control Division 9 in Phitsanulok.

The two were among three workers hired to take care of around 2,000 ducks at the farm before about 100 birds fell dead and were later found by livestock authorities to have the H5N1 strain of bird flu, he said.

Neither of them were checked if they had the virus despite having lived and worked inside the farm where the ducks were raised, said Public Health Minister Dr Mongkol na Songkhla.

Three others - two farm owners and a hired worker who also lived at the farm - were under a bird-flu observation programme, Kitti said.

Mongkol ordered the Phitsanulok disease control division to search for the missing men to ensure they were safe from the bird-flu virus, saying the two men might have just been frightened by the ducks dying of bird flu.

Kitti said some ducks had started dying in October and there were a huge number of deaths on January 9 when the farm reported to the provincial livestock authorities.

The Department of Livestock Development confirmed on Monday ducks at the Phitsanulok farm died of the H5N1 strain of bird flu. All remaining ducks were then culled and buried.

People who work in close contact with poultry and the transporting and slaughtering of poultry for food were of particular concern during this bird-flu alert period, said Mongkol.

Media campaigns on how to avoid getting bird flu were needed to raise public awareness, especially for the above-mentioned group of people, the minister said.

Education about bird flu had been done extensively since the first wave of bird-flu epidemics in 2004 and the public seemed to be well aware of the disease, he said.

"However, others are afraid to report to the authorities right at the beginning for fear of losing their animals," Mongkol said.

As for the high-risk group, including poultry farm workers and disease control teams, about 300,000 doses of human influenza vaccine were available for free at all provincial health offices, said Dr Thawat Suntrajarn, head of Disease Control Department.

The Public Health Ministry said it had stockpiles of about 800,000 tablets of the anti-virus oseltamiar (or Tamiflu) to treat up to 80,000 patients in the event of human infection.

About 800,000 health volunteers across the country were also ordered to stay on high alert and look for signs of bird flu in their communities to prevent the further spread of the virus to humans, said Mongkol.

Livestock Department head Yukol Limlamthong said separately that authorities were going to closely watch for bird flu during the upcoming Chinese New Year festival, which usually sees brisk trade of fowls across the country.

"We will step up preventative measures during the festival and other periods marked with extensive movements of birds," Yukol said.

Ethnic Chinese usually buy chickens and ducks as cooked offerings for Chinese New Year rites.

Yukol said his department was going to inspect slaughterhouses to ensure they would not spread the deadly virus. He said the Agriculture Ministry hoped to detect bird-flu at no more than 10 locations this year.

Currently, lab tests have confirmed there were bird-flu infections at a duck farm in Phitsanulok's Muang district. The whole district was now declared a "bird-flu outbreak zone", which barred poultry from being moved in or out.

The neighbouring province of Phichit has now set up checkpoints to prevent fowl being moved there.

Arthit Khwankhom

The Nation