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 Organization (WHO) said on Friday.
A spokeswoman for the U.N. 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, 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,” 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.
Experts believe it poses the greatest threat yet of a pandemic, a global epidemic of flu that could kill millions, if it becomes able to pass easily from human to human.
Keiji Fukuda, the WHO global influenza program coordinator, told a news conference ending the three-day experts’ meeting in Indonesia that what the WHO had been looking at in the cluster case was whether to move to a pandemic alert.
“The answer is clearly no. We see no evidence of the start of pandemic influenza,” he said.
The experts at the conference said that while Indonesia was making a substantial effort to combat the H5N1 bird flu virus, the situation was not yet satisfactory.
“Highly pathogenic H5N1 avian influenza is widespread and well established in Indonesia but the full extent is unknown. It is believed that large numbers of animal infections are undetected,” a joint statement by the experts said.
“The public is still lacking basic knowledge of the risks to their poultry and themselves and therefore their understanding of control methods in poultry and how to protect themselves is minimal.”
Indonesia has seen a steady rise in bird flu human infection and deaths. The virus has infected 51 Indonesians and killed 39 of them and is endemic in poultry in nearly all the country’s 33 provinces.