Michael Hopkin Infected Thai family alerts health officials to fresh danger.

Bird flu: close contact with birds may not account for all cases.

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An outbreak of avian influenza in a family in Thailand has raised fears that the virus might have been transferred directly between humans.

If the strain has mutated to allow easy person-to-person transmission, this opens up the possibility of a large-scale epidemic of the deadly virus. Officials are concerned about the case in Thailand, but say that so far it appears to be an isolated incident rather than the start of a major outbreak.

Thailand's Ministry of Public Health has confirmed that Pranee Thongchan, who died on 20 September in Bangkok, was infected with the H5N1 strain of the bird flu virus. She had been caring for her daughter, who died 12 days earlier of suspected bird flu in the northern province of Kamphaeng Phet.

The daughter is thought to have contracted the virus after dealing with infected birds at her home. But the mother, who travelled to the region when her daughter fell ill, did not come into contact with birds. This has sparked fears that the disease passed directly from one to the other.

Two more family members have fallen ill with influenza, including an aunt who lived with the sick girl and who has tested positive for H5N1. The region is under heavy surveillance from health officials.

Close quarters

Health authorities have raised the alarm about person to person transmission of avian influenza before: during a Hong Kong outbreak in 1997, and in Vietnam earlier this year. In both cases, the virus did not appear to spread very far.

Health officials remain hopeful that human-to-human transmission is still inefficient. In the latest case, the mother is understood to have had extensive, close contact with her daughter as she cared for her.

Nonetheless, the prospect of a widespread human outbreak is real. "We haven't seen any sustained [human] transmission, but this is a concern," says Maria Cheng, a spokeswoman for the World Health Organization (WHO). "It implies that the virus may have mutated to make it more transmissible."

WHO officials say they now plan to determine the genetic sequence of the virus to see if it has mutated and acquired the ability to jump more easily between people. "We're still waiting for results to characterize the virus. We don't yet have enough information," Cheng says.

Viral 'oomph'

Health experts fear that the H5N1 strain could mix with human viruses, giving rise to a virus that could infect humans much more easily. H5N1 has also recently been found in pigs, which are known to act as 'mixing vessels' for influenza viruses.

The steady flow of bird flu reports coming from Asia is worrying, says John Oxford, a virologist at Queen Mary's School of Medicine and Dentistry in London. "There are too many of these things happening to be complacent," he says.

Health officials need to secure the regions where the latest outbreak occurred before the virus gains the ability to move between humans easily, says Oxford. "For now, it's still giving the impression of being a virus without the necessary oomph to cause an epidemic."