Health officials identify flu "victims" with stickers inside an aircraft during a pandemic influenza simulation at Kuala Lumpur International Airport in Sepang Jan. 31, 2008. (Xinhua/Reuters Photo) Photo Gallery>>>

     BEIJING, March 3 (Xinhuanet)-- U.S. researchers have found influenza viruses coat themselves in fatty material that hardens and protects them in colder temperatures, thus explaining why winter is the flu season, according to Nature Chemical Biology Sunday.

    This butter-like coating melts in the respiratory tract, allowing the virus to infect cells, the team at the National Institutes of Health wrote in the journal.

    The new report could lead to new ways to prevent and treat flu, said NICHD Director Duane Alexander. The NICHD is one of the National Institutes of Health.

    Viruses cannot replicate on their own but instead must hijack a living cell. Influenza viruses have a membrane-like outer coating that they fuse to the victim cell.

    They inject genetic material into the cell, turning it into a virus factory.

    Some types of viruses simply explode out of these hijacked cells, but influenza instead "buds" out, and uses lipids such as cholesterol from the cells to make a membrane to help it do so.

    In cold temperatures, the hard lipid shell might withstand certain detergents, making it more difficult to wash the virus off of hands and surfaces.

    In warmer outdoor temperatures this protective coating melts, and unless it is inside a living person or animal, the virus perishes.

    The finding could also help scientists find new ways to eradicate influenza.

(Agencies)