Livestock officials spray disinfectant as they bury thousands of dead chickens in Thailand's Phitsanulok province, 377 km (234 miles) north of Bangkok, July 30, 2006. (Xinhua/Reuters Photo)

    BEIJING, Aug. 1 (Xinhuanet) -- Scientist who tried to combine a common flu virus with the H5N1 bird flu virus to create a pandemic virus that could be easily spread have failed, according to a report appearing in Tuesday's issue of Proceedings of the National Academy of Sciences in U.S.

    The finding suggests that it may be rather difficult for bird flu to mutate into a form that is easily transmissible among humans.

    Researchers from the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta worked in high-security labs and infected ferrets with genetically engineered versions of H5N1 avian influenza. They found that the animals did not infect other ferrets caged nearby. The hybrid flu versions also appeared less virulent than their parent strains.

    This study was conducted in order to better understand "the genetic changes that are needed for an H5N1 virus to acquire the genetic changes needed for better transmission," said Dr. Jackie Katz of the CDC's Influenza Branch.

    One way viruses can evolve into epidemic and pandemic forms is by mixing their genetic material with other viruses.So Katz's team tried mixing a sample of H5N1 virus taken in 1997 with genes from an H3N2 flu virus.

    They tested it in ferrets, which catch flu in a way very similar to people. Some of the mixtures made the ferrets sick, but infected ferrets put into a cage next to healthy ferrets did not pass on the virus.

    One leading expert called the test result a "small dose of reassurance," however, it wasn't shared by the head of CDC Dr. Julie Gerberding, "These data do not mean that H5N1 cannot convert to be transmitted from person to person. They mean that it is not a simple process," There are more than 50 possible combinations of the viruses, Gerberding added.

    However, Katz argued, "Of course the possibility was there that we would generate a strain that had the property of transmission." "That's what the question of the study was. But the study was conducted using the most stringent safety precautions that protected both the workers and the public."

    Katz said her team is planning to do more work with different versions of the avian and human influenza viruses. Enditem

    (Agencies)