News

Analysis of H5N1 avian flu viruses recovered from a large cluster of human cases in Indonesia showed multiple genetic changes as the virus moved through three generations of people, an as-yet unpublished report on the outbreak compiled for the Indonesian government revealed.

Viruses recovered from the last case in the cluster, a man who died on May 22, had accumulated 21 mutations, said the report, details of which were published Thursday by the journal Nature.

The significance of the mutations – and of the number accumulated – is unclear. And the fact that the changing virus did not continue to infect new hosts suggests that the mutations did not increase the virus's transmissibility among people.

Still, at the time of the late June meeting at which the report was presented, officials of the World Health Organization played down the virologic evidence at hand, speaking of a single mutation that they tracked in viruses passed from a 10-year-old boy in the cluster to his 32-year-old father, the last person to die.

A senior official defended WHO's decision not to release the information earlier, saying the material belongs to the Indonesian government and it is up to that country to determine whether or not to make it public.

Dr. Paul Gully, who has been seconded to WHO from the Public Health Agency of Canada, said the number of mutations does not change the fact the virus that spread in that cluster of cases reached a dead end.

“There's nothing in any of the sequences which would imply that any significant change (occurred), when it's added to the epidemiologic information and the clinical information” on the cases, Dr. Gully said in an interview from Geneva.

The cluster was the largest recorded to date, with seven confirmed and one suspect case in a family in the North Sumatran village of Karo. It is believed that the suspect case, who was never tested, passed the virus to six members of her family before she died in early May. Her 10-year-old nephew was among that second generation of cases; he is believed to have infected his father, who nursed the boy before his death.

This is thought to be the first time human-to-human-to-human spread of the H5N1 virus has been observed. Only one member of the cluster survived.

Since the H5N1 virus re-emerged in Southeast Asia in late 2003, there have been 229 confirmed cases and 131 deaths.