The boy died Wednesday in Nakhon Nayok province, and lab tests on Thursday confirmed he had been infected with the deadly H5N1 virus, said Thawat Suntrajarn, director-general of the Department of Communicable Disease Control.
"We can confirm that he died from the H5N1 strain of bird flu," Thawat said by telephone, adding that the boy died Wednesday afternoon.
The boy came from the Ongkarak district of Nakhon Nayok, 45 miles northeast of Bangkok.
Public health officials said the boy had been sick for nine days before being hospitalized, and that his parents failed to tell doctors that the family raised chickens at home. Officials said a relative, who lived in the same house, was raising about 10 chickens that had recently died.
The boy was taken to the hospital too late and was not given the proper medicine, said the official, who spoke on condition of anonymity because she is not authorized to speak to the media.
He is the 22nd person in Thailand to contract the H5N1 bird flu virus, and the 14th bird flu fatality. At least 70 people have died of bird flu in Asia.