Special report: Global fight against bird flu

    BEIJING, March 23 (Xinhuanet) -- H5N1 virus prefers to settle in cells deep within the lungs, rather than in the upper respiratory tract, as happens with human flu strains, two new studies have found.

Human-to-human transmission of H5N1 is highly unlikely, at least for now, experts say. (File photo)

    That may help explain why human-to-human transmission of the bird flu virus has so far not happened -- and might not happen in the future, Forbes.com reported Wednesday.

    Since 2003, the H5N1 virus has been found in Asia, Europe, Africa and the Middle East, and has led to the slaughter of tens of millions of domestic fowl. While infection has primarily been limited to birds, the virus has killed 103 people via bird-to-human transmission.

    Scientists worry, however, that the germ could mutate into a form that would make human-to-human transmission much easier, raising the concern that a pandemic among humans could break out worldwide.

    One of two studies published this week that looked at that possibility was conducted by researchers working at the University of Wisconsin and the University of Tokyo. They reported their findings in the March 23 issue of Nature.

    H5N1 was much less likely to bind to cells in the upper respiratory tract, the Japanese-American team found. The virus colonizes a much deeper, tough-to-access region of the lung-- making infection more difficult to spread and treat in humans, the researchers said.

    In contrast, common human flu strains prefer to bind to the upper respiratory tract cells. That makes sense, researchers say, because every time humans cough or sneeze, droplets from this area are easily expelled into the air, making human-to-human transmission of ordinary seasonal flu possible.

    The Japanese/American findings were echoed by a group of Dutch researchers in another paper, scheduled for release in the March 24 issue of Science but published early to coincide with the Nature study.

    The researchers at the University of Rotterdam again found that avian flu preferred receptors on cells deep in the lungs, and shunned binding with cells in the upper respiratory tract.

    All of this means that human-to-human transmission of H5N1 is highly unlikely, at least for now, experts say. However, any mutation or series of mutations that caused H5N1 to switch its preference could change all that. Enditem

    (Agencies)