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Genetically Unstable Bird Flu in Vietnam?
February 2, 2005
>> The eight patients were admitted to the Tropical Disease Institute in Hanoi capital on Tuesday and Wednesday, raising the total number of confirmed and suspected cases under treatment there to 21. Of the patients, three have been confirmed to contract the bird flu virus H5N1.
Since late December 2003, Vietnam has detected seven local H5N1carriers from the northern region and 10 others from the southern region, of whom 12 have died. It has also found that a 25-year-oldCambodian woman was infected with the virus. <<
There clearly has been a jump in the reported admissions of patients with bird flu symptoms in the Hanoi area. There has not been much detail on the recent cases, so it is not clear if they represent more "invisible" clusters of human to human transmission. The jump may be related to cooler weather in the north or a more easily transmitted virus.
The distribution of human and bird cases this year has some analogies with last season. The initial human cases were children in Hanoi, while most of the poultry infections were in the south. This year there are initial reports of cases in the south and none of the confirmed cases in the south have recovered. In contrast there has been one discharge in the north and two more are expected this week. The difference in recovered patients and number of cases may indicate two distinct H5N1's in Vietnam.
However, the rapid spread of the virus infecting ducks without causing symptoms is spreading and if there are two distinct genotypes in Vietnam, they may soon be co-circulating in the same region. Co-circulation leads to dual infections involving distinct genotypes, which leads to recombination. If the H5N1 in the north is more infectious and the H5N1 in the south is more lethal, a recombinant could be formed in ducks. This could lead to a virus with both properties, which would be an unfortunate evolution involving an increasingly unstable H5N1 genome.