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Poultry Raising Halted in Bird Flu Areas in Vietnam

Recombinomics Commentary
February 1, 2005

>> The city has around 210,000 ducks, which can carry the H5N1 virus without showing symptoms. Half are raised outdoors on small farms, allowing a potentially rapid spread of the virus.

Animal health officials said last week 31 of 148 samples taken from ducks in the city showed the presence of the virus.

Health workers and market inspectors will ensure no ducks are raised locally for a year and all ducks being transported into Ho Chi Minh City will be seized for destruction, often by burning, the Saigon Giai Phong newspaper said.

By Jan. 30, the H5N1 virus had killed or resulted in the slaughter of more than 1 million poultry in 31 of Vietnam's 64 provinces, the Agriculture Ministry said. <<

Controlling the spread of H5N1 avian influenza in asymptomatic ducks is difficult.  A high frequency of H5N1 positive ducks was noted above for Ho Chi Minh City.  Earlier reports indicted almost half of the tested ducks in Can Tho City were positive and the per cent positive in some areas of Quang Nam in the Central Highlands were approaching 100%.  Similar results were reported for other areas in the Mekong Delta.

Earlier WHO had issued a warning based on laboratory results which showed that the H5N1 that was lethal in people in Vietnam and Thailand last season could grow to high titers in the intestines of asymptomatic ducks.  The ducks appeared healthy, but excreted high levels of unusually stable virus.

Evidence for the asymptomatic ducks could also be seen in OIE reports.  In the January 7 report for Vietnam. There were 1,481 poultry destroyed in Can Tho City although there were no reported deaths.  On the same date Thailand reported destroying 19,000 poultry in the Muang district of Phitsanulok province, suggesting a significant presence of asymptomatic ducks in Thailand also.

Vietnam culled over 1 million birds in January with about a dozen confirmed human cases and more suspect cases.  However, Thailand has reported a much milder outbreak and no human cases.  Because of the similarity in the number of birds and people infected last year (especially if the unofficial H5N1 laboratory confirmed cases are added to the official total), as well as the apparently large numbers of asymptomatic ducks in Thailand this year, it is surprising that the differences in reported human and animal cases is so large.

Recently a patient from Cambodia was hospitalized in Vietnam with bird flu symptoms.  She died on Jan 30 and her brother died over 10 days earlier.  Officials noted that a large number of people with flu symptoms had been crossing the border from Cambodia to Vietnam and chicken and duck deaths are now being reported for Cambodia.  However, in November there were reports of large numbers of people from Laos and Cambodia crossing the border for treatment in Thailand.  In this area, the Vietnam border is only about 100 miles from the Thailand border, with Cambodia and Laos sandwiched between Vietnam and Thailand.  This region borders Dong Thap where some of the first human cases of H5N1 were located this season. Vietnam had halted the importing of poultry from Cambodia because of concerns about H5N1 infections.

These circumstances raise questions about the lack of detection or reporting of H5N1 in patients in Thailand.

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