March 15, 2007


extract from:
BirdLife Statement on Avian Influenza, 9 February 2007

"In Mongolia, at Erhel Lake, the main species found dead or dying with H5N1 in July 2005 were Bar-headed Geese and Whooper Swans Cygnus cygnus, and a small number were found to be infected with H5N1. Because this outbreak occurred after the Qinghai Lake outbreaks, researchers have speculated that migratory birds may have carried the virus to Mongolia. Bar-headed Geese and Whooper Swans also died in the Qinghai Lake outbreak, and one of the four strains of H5N1 isolated from Qinghai Lake was also isolated in Erhel Lake. However, both these species would have arrived to breed in Mongolia several months earlier, and during the outbreak the birds would have been near to completing their annual feather moult, during which they are sedentary. Thus it seems unlikely that they carried the virus from Qinghai to Lake Erhel. There were no signs of large mortality events in eight wetlands within 450 km of Lake Erhel and 4,119 H5N1 tests of healthy wild birds carried out during the same period were negative. Although a large number of birds died at Erhel Lake, few actually tested positive for the virus and it was estimated that only 0–1% of the living or dead birds were infected with H5N1. These facts point to the source of H5N1 infection being local to Lake Erhel and that the infected wild birds did not spread the disease to new locations, or even among themselves to any significant extent."

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