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H5N1 Wild Bird Flu Confirmed in Erhel Lake Mongolia
August 18, 2005
As of today, preliminary tests from one dead whooper swan collected in Mongolia have shown the presence of the H5N1 strain of Avian Influenza using RT-PCR, while results from 30 live whooper swans living at the same site and also a nearby lake were negative for the virus. Samples collected from other live birds at the two sites, including sixty ruddy shelducks, twenty-four bar-headed geese, and twenty-five black-headed gulls, were found to be negative for the virus.
The above comments confirm that H5N1 wild bird flu has migrated to Mongolia. In an earlier report, the deaths of swans, geese, and gulls were confirmed to be H5 positive, but questioned remained as to the relationship between the dead birds in Mongolia and earlier outbreaks at Qinghai Lake and Chany Lake.
Not unexpectedly, the H5 was confirmed to be H5N1. Sequencing will almost certainly show that the H5N1 in Mongolia is closely related to the H5N1 in China and Russia. In China, the isolates from bar headed geese were tested in a pathogenicity test that killed experimental chickens in 20 hours. The sixteen isolates at Qinghai Lake were closely related to each other and the OIE report from Novosibirsk indicated the isolates there were closely related the Qinghai Lake isolates. The isolates also had the unusual ability of causing fatal infections in waterfowl such as ducks and geese.
The ability to cause fatal infections is dependent on several conditions, including the level of H5N1 in feces and dilution factors. In nature reserves with large lakes, the feces are diluted by the volume of water. However, in smaller lakes and ponds near farms, the concentration of virus is higher.
Migratory birds are clearly spreading the H5N1 wild bird flu. The dead birds in Mongolia were are remote lakes, eliminating domestic birds as the source of infection. The H5N1 outbreaks along migratory paths also implicates the wild birds as indicated in OIE reports from Qingahi Lake, Tacheng, Changji, Novosibirsk, and Pavlodar.
Because the H5N1 in these birds is highly pathogenic, the level in feces may be too low for detection, yet capable of efficient transmission. The OIE reports implicate open water sources as means of transmission. Because of the virulence of the H5N1, its path was clearly seen. The HPAI H5N1 in Russia, Kazakhstan, and Mongolia have been reported for the first time.
These outbreaks are expected to increase as more birds migrate from southern Russia and Qinghai Lake toward warmed regions as the fall season nears.