A 17-year-old Thai has died of the H5N1 bird flu virus, the country’s first death this year as it battles fresh outbreaks of the disease, a senior health official said on Wednesday.

The young man died on Monday in the northern province of Pichit, where authorities have slaughtered hundreds of birds and restricted poultry movement in a bid to stamp out Thailand’s first outbreak in eight months.

“The final lab test confirmed that he died of bird flu,” Kamnuan Ungchusak, head of the Health Ministry’s epidemiology bureau, told Reuters by telephone from the hospital where the youth died.

He is believed to have caught the virus while helping his father bury dead chickens last week.

The father showed no flu-like symptoms of the virus which has killed 15 Thais since it swept across parts of Asia in 2003. The last Thai victim, a five-year-old boy, died in December last year.

“We have quarantined the family and there is no report of a new case yet,” Kamnuan said.

Not including this latest death, bird flu has killed 133 people worldwide since the virus re-emerged in Asia in 2003, the World Health Organization says.

At present, H5N1 remains essentially a disease of birds and is hard for people to catch.

But scientists fear the virus could mutate into a form that spreads easily among humans and trigger a pandemic in which millions could die.

The outbreak in Pichit, one of seven high-risk Thai provinces where surveillance was stepped up this month, was confirmed by the Agriculture Ministry on Tuesday, but the source of the infection was not known.

The U.N. Food and Agriculture Organization (FAO) called for an “intense investigation” of the outbreak. It said Thailand had done a good job in fighting the virus so far, but it may need to fine-tune its surveillance.

“Clearly they have pushed this thing down to the level of almost non-existence, but either it’s been reintroduced or it has persisted and at such a low level it did not cause any significant blips,” Laurence Gleeson, a senior FAO official in Bangkok, told Reuters.

Thailand was slow to respond to bird flu when it first began ravaging poultry flocks in late 2003, badly damaging what was the world’s fourth largest chicken export industry.

Critics accused the government of trying to cover up this latest outbreak, a charge denied by Livestock Department officials who said they had informed the public as soon as tests confirmed the presence of H5N1.

Gleeson said the FAO, which has stressed the need for rapid and transparent reporting of outbreaks, had no complaints about Thailand’s reporting procedures.