H5N1 mutated in Indonesia - WHO

The H5N1 bird flu virus mutated somewhat among Indonesians in the largest known human cluster, but did not evolve into a more transmissible form, the World Health Organisation (WHO) said yesterday.

A spokesman for the UN agency, Maria Cheng, said the result came from its investigation into a cluster of cases in northern Sumatra, where the virus killed seven members of a single family in May.

"There was a mutation found," she told Reuters in Geneva, in response to a query. "But it did not mutate into a form that is more transmissible because it didn't seem to go beyond the cluster."

Malik Peiris, a leading H5N1 expert from Hong Kong, told reporters on the sidelines of a bird flu experts' meeting in Jakarta that it was common for the influenza virus to mutate.

"Influenza viruses always mutate. That's of course the reason why people are concerned that as we go on longer and longer the virus may change to become more transmissible. But that does not happen so far."

The mutated virus was detected in samples taken from the last two victims in the cluster - a son who transmitted it to his father - providing the clearest proof yet of human to human transmission, Dr Cheng said.

"In the past we haven't had such definitive laboratory evidence to prove human to human transmission but in this case we do."

But three weeks later, the man's wife has not shown any signs of the disease, she added.

"We did not detect any transmission so it was a dead-end chain of transmission," Dr Cheng added.

Indonesian and WHO officials closely monitored more than 50 contacts of the victims in the northern Sumatra case, keeping them in voluntary home quarantine following the outbreak, but none developed symptoms, according to the Geneva-based agency. The H5N1 strain of avian influenza has spread rapidly from eastern Asia in recent months. It almost exclusively infects birds but has killed 130 people since 2003, mostly in Asia.