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China Bird Flu Appears to Mutate

A woman and her daughter are frightened while ducks approach closely for food at an amusement park in Beijing, China, Wednesday, April 3, 2013. Scientists taking a first look at the genetics of the bird flu strain that recently killed two men in China said Wednesday the virus could be harder to track than its better-known cousin H5N1 because it might be able to spread silently among poultry without notice. The bird virus also seems to have adapted to be able to be able to sicken mammals like pigs. (AP Photo/Alexander F. Yuan)

A woman and her daughter are frightened while ducks approach closely for food at an amusement park in Beijing, China, Wednesday, April 3, 2013. Scientists taking a first look at the genetics of the bird flu strain that recently killed two men in China said Wednesday the virus could be harder to track than its better-known cousin H5N1 because it might be able to spread silently among poultry without notice. The bird virus also seems to have adapted to be able to be able to sicken mammals like pigs. (AP Photo/Alexander F. Yuan)

Beijing — In a worrisome sign, a bird flu in China appears to have mutated so that it can spread to other animals, raising the potential for a bigger threat to people, scientists said yesterday.

So far the flu has sickened nine people in China and killed three. It’s not clear how they became infected, but there’s no evidence that the virus is spreading easily among people.

But the virus can evidently move through poultry without making them sick, experts said, making it difficult to track the germ in flocks.

The findings are preliminary and need further testing.

In the wake of the illnesses, the Chinese Center for Disease Control and Prevention shared the genetic sequence of the H7N9 virus with other scientists to help study how the virus might behave in different animals and situations.

One scientist said the sequence raises concern about a potential global epidemic, but that it’s impossible to give a precise estimate of how likely that is.

“At this stage it’s still unlikely to become a pandemic,” said Richard Webby, director of a World Health Organization flu center at St. Jude Children’s Research Hospital in Memphis, Tenn.

“We should be concerned (but) there’s no alarm bells ringing yet,” he said.

The virus has genetic markers that would help it infect people, Webby said. That makes him worry about a pandemic a bit more than he does for other bird flu viruses, such as the H5N1 virus that emerged a decade ago, he said.

“The tentative assessment of this virus is that it may cause human infection or epidemic,” said Dr. Masato Tashiro, director of the WHO’s influenza research center in Tokyo and one of the specialists who studied the genetic data, “It is still not yet adapted to humans completely, but important factors have already changed.”

Flu viruses evolve constantly, and scientists say such changes have made H7N9 more capable of infecting pigs.

Pigs are a particular concern because bird and human flu viruses can mingle there, potentially producing a bird virus with heightened ability to spread between humans, said Dr. William Schaffner, a flu expert at the Vanderbilt University School of Medicine. That’s what happened in 2009 with swine flu.