A one-year-old boy has been diagnosed with the lethal H5N1 strain of bird flu in Bangkok, Thailand's director general of disease control has said.
Thai authorities have been monitoring the spread of the virus
Tests confirmed the boy had the virus but he was expected to make a full recovery, Thawat Sunthrajarn said.
Of the 21 people who have contracted bird flu in Thailand, 13 have died.
Scores of people and thousands of fowl have died of bird flu since 2003, and there are fears of a pandemic if the virus mutates to pass between humans.
So far, all the humans killed are believed to have contracted the virus through contact with infected birds.
Mr Thawat told the Associated Press news agency the latest Thai citizen to contract the virus had been living in close proximity to live poultry.
Several fighting cocks and a chicken kept in the same house as the boy had died soon after his flu symptoms were reported, he said.
Mr Thawat did not name the boy but said "he is recovering and is almost back to normal".
He said the boy's grandmother had also reported flu-like symptoms but tests had yet to prove whether she had the same infection.
Officials from Cambodia, Laos, Myanmar, Thailand and Vietnam met in Bangkok last week to discuss measures that could curb the disease's spread.
Thailand has promised $2.5m (£1.7m) to its neighbours in the event of an emergency.
The Thai government also announced last week that it will start manufacturing a generic version of the drug Tamiflu, which is widely believed to help reduce bird flu symptoms in humans.
Earlier this week, China reported two fresh outbreaks of the deadly H5N1 strain of bird flu in its poultry, sparking fears of a spike in the disease as winter approaches.
The new cases were detected in Fuxin and Jinzhou in the north-eastern province of Liaoning.
There have now been six bird flu outbreaks in China in the past month.
No human infection has been confirmed in China, but the WHO will this weekend test samples from three Chinese people suspected of having the disease.
Chinese Premier Wen Jiabao said the country faced a "very serious situation" and urged areas with a large number of poultry to draft emergency plans.
About 1,100 chickens died in the latest outbreaks in Liaoning.
Thousands more have been culled on the orders of the authorities, the state-owned Xinhua news agency says.