The spate of human bird flu cases in Vietnam this year suggests the deadly virus may be mutating in ways that are making it more capable of being passed between humans, according to a World Health Organization (WHO) report.
World Health Organisation
The finding points to the greatest fear of health experts that the H5N1 virus could unleash a pandemic and kill millions around the globe if ever it gained the ability to be transmitted among humans efficiently.
Although investigators could not prove human-to-human transmission had occurred, the report said that "the pattern of disease appeared to have changed in a manner consistent with this possibility".
"They [findings] demonstrate that the viruses are continuing to evolve and pose a continuing and potentially growing pandemic threat," the report said.
Klaus Stohr, WHO's global influenza programme co-ordinator, told a news briefing in Geneva: "We don't know whether the pandemic will occur next week or next year . . . we should continue very intensively with pandemic preparations."
H5N1 made its first known jump to humans in Hong Kong in 1997 and experts have always established that the mode of transmission was through direct contact with birds.
But the virus has mutated since, raising fears among experts that it may one day adapt in humans and become easily passed between them, setting off a pandemic.
In the six-page report, produced after an expert meeting in Manila from May 6-7th, the WHO said at least 92 adults and children in Vietnam, Thailand and Cambodia had become ill after being infected with H5N1 since late 2003, and 52 of them had died.
More clusters of infections involving household members have occurred, opening the possibility that "person-to-person transmission" may have taken place, the WHO said.