BEIJING, Dec. 19 (Xinhuanet) -- No human-to-human transmission of bird flu has been found so far, but subtle mutations in the virus are bringing the world closer to a pandemic, the UN's coordinator on avian influenza has warned recently.

   "There are some subtle changes in the genetic makeup of H5N1 which suggest that it is making some of the mutations that would enable it to have a higher likelihood of being able to become a human-to-human transmitted virus," said David Nabarro in Phnom Penh during a one-day visit to Cambodia, which has seen at least four human bird flu deaths.

    "Virologists who study these things say do not get complacent. It is quite feasible that H5N1 could mutate. The fact that it has taken some years should not lead you to believe that we are through the worst."

    He warned that there are difficulties stockpiling enough anti-viral medicines to combat the illness.

    "We all would like there to be much more stock of anti-viral medicines. We are in a bit of difficulty because the production capacity, particularly of (Tamiflu), is quite restricted," he said, adding that the UN was in regular talks with drug manufacturers to build up stocks. 

    The bird flu virus has killed more than 70 people through Asia since 2003 and resulted in the culling of millions of birds, dealing a huge blow to regional poultry industries. Enditem