Officials of the World Health Organization said they have seen no evidence to support the claim. They suggested Indonesia should share the data so other scientists can help investigate whether the virus is undergoing changes that might increase the pandemic risk it poses.
"I think it would be important to know the entire (genetic) sequence of these Indonesian viruses before we can make any assessments about virulence changes or transmissibility (to) host changes," Dr. Michael Perdue of the WHO's global influenza program said from Geneva.
"We would certainly look forward to having the full sequence and antigenic analysis of these viruses reported as soon as possible."
Indonesia has not shared the findings with the WHO. And the country has only sporadically shared viruses with the global health agency since the beginning of 2007 in a dispute over access to pandemic vaccines.
In Jakarta, Bayu Krisnamurthi, the head of Indonesia's avian flu control commission, told reporters that it appears recent human cases have become infected from less intensive exposure to the virus than previously had been the case.
That raises the suspicion, he suggested, that the virus has adapted to more easily infect humans.
It was not clear which cases Krisnamurthi was referring to or how exposure was measured.
It's not even clear how exposure could be measured in many of Indonesia's cases. A substantial portion of the 99 human infections there have occurred in people for whom no link to infected poultry was ever discovered.
In a presentation last fall, officials of the Ministry of Health told the WHO that in at least one-third of their cases, they could find no firm proof of how the people had come in contact with the virus.
"Even the updates I've seen from the Ministry of Health, still there's a large percentage of the cases they can't find any connection" to infected birds, Perdue said.
In a related issue a microbiologist from Krisnamurthi's commission told Reuters news agency that molecular study of the viruses has revealed changes.
"Virus samples from poultry cases have increasingly shown a similarity in their amino acid structure to virus samples extracted from humans," Wayan Teguh Wibawan said.
Perdue said it would be important to know if the Indonesian scientists are drawing the conclusions by studying the entire genetic blueprints of viruses isolated from human cases, or if they are looking only at a portion of the hemagglutinin gene.
Hemagglutinin plays a key role in the ability of influenza viruses to infect various hosts, whether they are birds, people or other mammals.
And early efforts to figure out why the H5N1 virus can infect some people but very rarely does so focused on the notion that the H5N1 virus was better suited to attaching to receptors more commonly found in the cells of birds than in the respiratory tracts of humans. It was thought mutations at the receptor binding site might be all that was needed to turn this bird virus into a human virus.
But recently scientists have begun to question that theory. In a talk at a recent microbiology conference in Toronto, influenza expert Dr. Malik Peiris said work from a number of laboratories suggests the whole idea should be revisited.
"It still remains an open question what it will take to allow this virus to go human-to-human," said Peiris, who is from the University of Hong Kong.
Perdue concurred. "Nearly all influenza specialists now agree that single changes in a particular region alone will not likely set off a major change."
Indonesia has only shared H5N1 viruses in a limited fashion over the last half year, using the viruses as leverage in a bid to give H5N1-affected countries more control over the science conducted on viruses collected within their borders.
Health Minister Siti Fadilah Supari announced in early February that her country would not share viruses unless it received guarantees those viruses would not be used to make vaccine without Indonesia's permission.
Since that time, she has gone back and forth on the issue, promising at times to resume sharing viruses with WHO reference laboratories. But so far, specimens from only two of the 18 cases that have occurred in the interval have been sent out of the country.
