BioEd Online

Indonesia has become the fourth country in southeast Asia to report someone infected with a deadly strain of avian flu virus. The H5N1 strain has already killed at least 54 people in Vietnam, Cambodia and Thailand.

The infected man is a farm labourer who was exposed to sick chickens when a wave of avian flu swept over the southern Sulawesi island earlier this year.

Indonesian health officials took blood samples from 81 people who had been exposed. The samples were analysed in a laboratory in Hong Kong, and one was found to be positive.

Officials first found this positive result in March (see ' Bird flu spreads among Java pigs'). They took several weeks to confirm it because they cound not find the man concerned, but he was tracked down and the case verified in May.

The man shows no symptoms, but his blood carries antibodies to the H5N1 strain. It is not unprecedented for otherwise healthy poultry workers to test positive for the virus, say health officials: at least five have done so in Vietnam.

But the officials warn that as more people become infected, the chance increases that a deadly new pandemic virus will emerge against which humans have no defence. This could happen if a person becomes infected with an avian flu virus and a normal human flu virus at the same time, because the two viruses could swap genes.

Concerns have been raised about the ability of Asian countries, including Indonesia, to keep up sufficient monitoring efforts, given limited resources.

Indonesian health experts say that their virus is genetically distinct from the H5N1 viruses isolated from sick chickens in other southeast Asian countries. It is too early to say if this means that it is therefore less virulent.