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 Wednesday.
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 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.
One scientist said the sequence raises concern about a potential global epidemic, but that it's impossible to estimate 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.
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, 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, 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.