Checks into bird flu cluster reassuring -CDC head

WASHINGTON, May 25 (Reuters) While human-to-human transmission is the No. 1 suspect in a worrisome cluster of bird flu cases in Indonesia, once-fearful islanders have begun to cooperate and experts do not suspect a wider outbreak of the virus, a top U S health official said.

Villagers on the remote north Sumatran island have shared information about the family cluster, in which seven people have died, and what has been learned so far is reassuring, said Centers for Disease Control and Prevention director Dr Julie Gerberding.

The villagers are Christian, and some initially blamed the government of Muslim-majority Indonesia for the deaths and declined to cooperate with health workers, she said.

No one has yet found evidence of an infected chicken or other animal that could have infected the family members, who include a woman, her brother, some children and other relatives.

''The concern that has been raised ... is the potential for evidence for human-to-human transmission in this outbreak,'' Gerberding told reporters in a telephone briefing from Geneva, where she is attending a World Health Organization assembly.

''This is the leading hypothesis that is under investigation. The likely source was poultry exposure, as we have seen time and time again.'' But the case may represent what is known as tertiary transmission -- someone may have been infected by a chicken and infected a relative, who in turn infected someone else.

While rare cases of human-to-human transmission have been seen before -- in Thailand and Vietnam -- doctors believe that one person only infected one other in those instances and the chain of transmission stopped there.

''A person-to-person-to-person transmission chain is very important ... that is why there has been such attention and such an effort,'' said Gerberding, who had been briefed by WHO experts and CDC epidemiologist Dr Tim Uyeki, who is in the village of Kubu Sembilang where the seven victims came from.

NO EVIDENCE OF MUTATION ''Obviously the worrisome possibility is this represents a change in the virus,'' Gerberding added. But she stressed, ''We have not seen any evidence of that.'' ''What we have seen is a virus that is not particularly transmissible but in the setting of very close contact, people can pick it up.'' It is possible these family members, all related by blood, have a genetic susceptibility to infection, she said.

Gerberding said it was important to note that no one outside the family had been found to have been infected, and the infections seem to have happened as people cared for their sick relatives.

She said she was reassured by the CDC's sequencing of virus samples taken from some of the victims.

''There is no evolution of the virus or genetic changes that would suggest a change to a more virulent or transmissible form,'' she said. And there was no evidence the virus was resistant to Roche AG's Tamiflu, the main treatment for H5N1.

The village is small, Gerberding, and villagers are being treated with Tamiflu, known generically as oseltamivir. When given early, the drug can reduce the severity of flu infection and can prevent infection if taken before a person is exposed.

''The good news about the situation is that we got there early and the WHO was able to gain access to a community that is in a very remote part of the world and a part that doesn't necessarily trust Western medicine or the kind of science approaches that we would consider our main contribution to understanding disease outbreaks,'' Gerberding said.

''This is a Christian community in a pretty remote area on an outlying island,'' she added. Indonesia is overwhelmingly Muslim and there has been some mistrust between Christian communities and the government.

''Yes, there were apparently some members of the community that expressed concern that the government was at fault,'' Gerberding said.

But she said the WHO team now reported that villagers were cooperating with them.

REUTERS DH RN0553