The first human case of bird flu was identified in Indonesia after a poultry worker tested positive this month, a World Health Organisation (WHO) official said on Thursday.

But the poultry worker shows no symptoms of the disease, and due the low concentration of antibodies he no longer carries the virus, the Jakarta-based official said.

The poultry worker was first tested in March after an outbreak hit South Sulawesi province killing around 25,000 fowl.

Out of the 81 people tested, his test at a Hong Kong laboratory showed a positive result, prompting another examination.

“The second test showed the exact same result as the first test, what’s called a very low concentration of antibody,” said Steven Bjorge, an epidemiologist.

“If the second (test) showed a high concentration of antibody that would indicate that he had a recent infection.”

The second test was completed this month as health officials had lost track of the person after his poultry business went bankrupt.

The H5N1 virus has killed 54 people across Asia, including 38 Vietnamese, 12 Thais and four Cambodians since late 2003.

Since the disease emerged in late 2003 in Indonesia, health authorities have tested more than 1,000 samples from poultry workers, veterinarians and others exposed to the deadly disease.

Indonesia’s agriculture ministry has reported sporadic H5N1 outbreaks in fowl in South Sulawesi, West Java and Central Java in the first three months of this year, and had confirmed the virus had jumped species and was discovered in pigs last month.

Scientists fear the avian flu, which is infectious in birds but does not spread easily among humans, could mutate into a form capable of generating a pandemic in which millions of people without immunity could die.