A four-year-old boy who died of bird flu (searchin Thailand (searchbecame Asia's 21st victim of the disease Thursday, while Singapore (search) prepared to kill healthy chickens as practice for a possible outbreak in the city-state.

Japanese authorities, meanwhile, said a man who developed a brief fever after handling pet chickens who died of bird flu at a home in southern Japan was unlikely to have been infected with the human form of the disease.

The disease so far has jumped to people only in Thailand -- where it has killed seven -- and in Vietnam (search-- where it has killed 14. The illness is highly contagious among birds but has shown no sign of being easily transferrable between people, whose illnesses have largely been traced to contact with sick birds.

Asian countries have slaughtered at least 80 million chickens to curb the virus, which has rapidly spread through the region's poultry farms, especially in Southeast Asia, where Cambodia, Indonesia and Laos also have been affected.

China has widespread poultry infections, but has said it is confident its anti-flu measures will contain the disease's spread. However, new cases are being reported nearly every day.

Pakistan and Taiwan have been hit with milder bird flu strains not believed to be dangerous for people.

Singapore, still free of the disease, planned to gas and incinerate 5,000 chickens at a remote farm later Wednesday to practice culling in case the virus spreads to the city-state.

"Culling chickens is not as easy as it sounds," Goh Shih Yong, a spokesman for the Agri-Food and Veterinary Authority, said in a letter Wednesday in the Straits Times newspaper. "We are using 5,000 chickens in the exercise to ensure that we are prepared to do full-scale disease eradication."

The latest victim in Thailand died Feb. 3 in the northeastern province of Khon Kaen and tests confirming that he had the deadly H5N1 strain of bird flu were announced Wednesday.

The disease is known to have killed six children and one adult in Thailand so far, and is suspected to have infected about 20 people. The Thai government has culled more than 26 million chicken and other fowl.