JAKARTA — Limited human-to-human transmission of bird flu might have occurred in an Indonesian family but there is no evidence the virus has mutated to allow it to pass easily among people, the World Health Organisation said.
Seven members of the family from a village in north Sumatra died this month and the WHO and Indonesian health officials are baffled over the source of the H5N1 avian flu virus.
But they say there is no evidence the virus has passed to anyone else outside the initial cluster of up to eight people.
It is the largest family cluster known to date, the WHO has said, and such clusters are looked on with far more suspicion than isolated infections because they raise the possibility the virus might have mutated to transmit efficiently among humans.
That could spark a pandemic, killing millions of people.
"To date, the investigation has found no evidence of spread within the general community and no evidence that efficient human-to-human transmission has occurred, the WHO said in a statement posted on its Web site at http://www.who.int.
It said one of the family members, a 32-year-old father, died on Monday after caring for his ailing son.
The agency said such close contact was considered a possible source of infection. However, genetic sequencing of the virus—which would enable scientists to tell if it has mutated—showed nothing unusual.
"Sequencing of all eight gene segments found no evidence of genetic reassortment with human or pig influenza viruses and no evidence of significant mutations," the WHO statement read.
"The human viruses from this cluster are genetically similar to viruses isolated from poultry in North Sumatra during a previous outbreak."
Sick poultry has been the source of H5N1 infection for the vast majority of human infections worldwide. The virus can also infect pigs.
Worrying
The U.N. agency, though, was also keen not to play down the seriousness of the case.
"This is the most significant development so far in terms of public health," Peter Cordingley, spokesman for the West Pacific region of the WHO, told Reuters Television in the Philippine capital.
"We have never had a cluster as large as this. We have not had in the past what we have here, which is no explanation as to how these people became infected."
"We can't find sick animals in this community and that worries us," he added.
Limited transmissions between people—the result of very close and prolonged contact when the sick person is coughing and probably infectious—are very likely to have occurred before in Hong Kong, Vietnam, Thailand and Indonesia.
The WHO, giving its first details of the family cluster, said investigators were trying to figure out just what happened in the Sumatran village, where a woman appeared to have been the first to become ill at the end of April.
"Preliminary findings indicate that three of the confirmed cases spent the night of 29 April in a small room together with the initial case at a time when she was symptomatic and coughing frequently," the WHO Web statement reads.
"All confirmed cases in the cluster can be directly linked to close and prolonged exposure to a patient during a phase of severe illness. Although human-to-human transmission cannot be ruled out, the search for a possible alternative source of exposure is continuing," the WHO said.
The WHO statement appears to have affected some Asian markets early on Wednesday and helped the dollar edge up against the yen and the Taiwan dollar.
A virologist said there was no cause for alarm.
"This father has been (caring for) his son and contracted H5N1 from this. Is it any different from the case in Thailand when the mother was nursing her daughter in hospital? The published case report also concluded that this was probable human-to-human transmission from close contact," said Julian Tang, a microbiologist at the Chinese University in Hong Kong.
"I don't see why there is so much excitement about this case," he added.
Bird flu has killed 124 people in ten countries since it re-emerged in Asia in 2003. It remains essentially a disease in birds and has spread to dozens of countries in wild birds and poultry.
An Iranian medical official told Reuters on Monday that a 41-year-old man and his 26-year-old sister from the northwestern city of Kermanshah had tested positive for bird flu.
But Health Minister Kamran Lankarani denied this although international health officials are still investigating.
The two siblings were among five members of a family who became sick and the other three remain in the hospital.
