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New Bird Flu Sequences in Vietnam
January 25, 2005
>> According to officials at the UN Food and Agriculture Organization (FAO), the avian-flu virus in Southeast Asia needs closer monitoring in order to further understand the character of the virus and the "dynamics of the disease".
"There has been a drift in the virus in January 2005 when compared to what it was in January 2004," Juan Lubroth, senior officer at the FAO's animal-health division, told Inter Press Service, referring to the changes that take place in the virus over a period of time. "This is the case throughout the region," he said. <<
The drift in the 2005 H5N1 avian influenza virus is cause for concern. Although not unexpected, new sequences can bring new problems. H5N1 is currently very unstable in Asia. It drifts and shifts via recombination and new sequences provide more sources of more drifting. The grey herons discovered last month in Hong Kong were distinct from the geese or grey herons isolated in Hong Kong in 2002 and these late 2004 novel genes were indicators of a new season.
Now sequence information is beginning to emerge on the 2005 virus. The drifting is probably more than was seen for the clusters in Vietnam and Thailand over the summer (including the tiger outbreak at the Sri Racha Tiger Zoo). Those sequences were virtually identical to January 2004 sequences. Now the January 2005 sequences have drifted (recombined) to create new genes which are associated with more frequent reports of family clusters consistent with human to human transmission, as well as infections from swimming or bathing in waters containing dead poultry.
H5N1 has been steadily accumulating these polymorphisms as it expands its host range. These more recent H5N1 isolates do not have reassorted human genes, although some have reassorted and recombined with H9N2 genes. Swine in Korea have H9N2 genes reassorted and recombined with human WSN/33 genes.
These new polymorphisms generated via recombination have clearly altered the "dynamics of the disease" in the past and appear to be doing so again in 2005 in Vietnam. Similar changes should be expected throughout eastern and southeastern Asia.