The tigers have been dying at the Sriracha Tiger Zoo in central Chonburi province since Sept. 14, said Charal Trinvuthipong, director of the Bird Flu Prevention and Elimination Center. The animal park was forced to close to the public while authorities investigated.
"We've discovered that all 23 dead tigers had bird flu," Charal said. "We've found that another 30 tigers are sick. We believe that the tigers contracted bird flu because they ate chicken carcasses, and we believe the carcasses had bird flu."
But Fadela Chaib, a spokeswoman for the World Health Organization, told reporters in Geneva that there was little risk of transmission to humans because "tigers aren't a receptacle for the human virus."
Thai veterinarians were checking for the disease at chicken farms in the province, where the zoo got the birds that were fed to the tigers, Charal said. The chickens were ordered culled.
The more than 400 tigers at the zoo are regularly fed raw chicken, a zoo official said on condition of anonymity.
During this year's first wave of bird flu, a clouded leopard and a white tiger contracted the virus at another zoo in Chonburi, the same province where the tiger facility is located. The leopard died, but the white tiger recovered.
News of the latest tiger deaths came as the government prepared to cull ducks, which are thought to play a major role in spreading the deadly H5N1 strain of bird flu, which has killed 31 people in Thailand and Vietnam and forced the culls of tens of millions of birds this year.
Although the virus has most commonly been found in chickens, scientists fear it could mutate by linking with a human flu virus, sparking a global pandemic.
After Thailand announced its first probable case of human-to-human transmission of bird flu, Prime Minister Thaksin Shinawatra vowed to fight the outbreak and rid the country of the disease by the end of October.
International experts, however, have said the virus seems to be entrenched in the region and it is likely to take years to control its spread.
On Monday, the Bird Flu Prevention and Elimination Center — a government committee assigned to combat the disease — said it would target ducks raised domestically by farmers and that are allowed to wander in the open.
Wild birds are thought to be responsible for spreading the disease and reintroducing it to areas where it had been brought under control, and ducks are believed to be able to carry the virus without succumbing to it.
Deputy Prime Minister Chaturon Chaisaeng said the government would buy ducks from farmers before December, the height of flu season, and cull them. He suggested the same plan might later be applied to fighting cocks and free-range chickens.
Cock fighting is hugely popular in Thailand, and owners have resisted previous culls by hiding their expensive birds.
By Alisa Tang