H7N9 flu outbreak: Ducks may be source

SINGAPORE - The avian flu strain that has killed 17 people in China may have originated in wild ducks, says a Singapore scientist.

Proteins on the virus' shell appear to have come from the birds, said Associate Professor Gavin Smith of the Duke-NUS Graduate Medical School Emerging Infectious Diseases programme. This could have happened years, not months, ago.

Prof Smith's view goes at least some way towards answering the burning questions that have emerged since the start of the outbreak: Where did the new H7N9 virus come from, and how likely is it to cause a pandemic?

So far, more than 80 people in China have fallen ill. The World Health Organisation has confirmed about 40 per cent of sufferers had no contact with fowl. And Chinese officials are investigating the possibility that the virus has spread from human to human.

"The likelihood is that there's been a change in the nature of the virus that allows it to infect humans more readily," said Prof Smith, who is studying its genetic sequence.

Research in Japan and the United States has also uncovered mutations that allow the H7N9 virus to grow more efficiently in humans' respiratory tracts - which are cooler than those of birds.

People in Asia generally have a high exposure to avian flu because they come into relatively frequent contact with chickens, said Associate Professor Richard Sugrue, a virologist at Nanyang Technological University.

How sick the patients get depends on how well the particular strain they have caught enters human cells and replicates itself, Prof Sugrue explained.

For example, the H5N1 form of the virus can get into many types of cells and multiply there, causing severe illness. By contrast, seasonal flu strains enter just those cells in human airways.

Worryingly, domestic poultry do not seem to have fallen very ill from the latest H7N9 infections. That could lead to a "silent" outbreak in China and other nations, wrote US Centres for Disease Control and Prevention (CDC) flu experts Timothy Uyeki and Nancy Cox in The New England Journal of Medicine last week.

But how widespread and severe will the human H7N9 outbreak be? Will it be like H1N1 in 2009 - easily passed from person to person but remained mild?

Or will it resemble H5N1, which causes severe illness in humans but has limited transmission between people? "It's almost impossible at the moment to predict what will occur with the H7N9 virus," said Prof Smith.

Adjunct Associate Professor Lim Poh Lian, head of infectious diseases at Tan Tock Seng Hospital, said it could turn out to be like the 2009 H1N1 outbreak, when the death rate appeared high at first. This was because only severe cases were counted as people with milder forms of the illness did not know they had it.

"It's very early still in the evolution of the outbreak," she said.

The coming weeks will reveal which direction the H7N9 outbreak is headed, wrote the CDC flu experts. But developing vaccines is slow work. "We cannot rest our guard," they wrote.

caiwj@sph.com.sg


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