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Asymptomatic H5N1 Ducks in Central Highlands of Vietnam
June 24, 2005
>> One-fifth of total waterfowl flocks in Vietnam's central Quang Tri province have just been found to contract bird flu virus strain H5N1, local newspaper Saigon Liberation reported Friday.
The provincial Veterinarian Bureau has culled over 23,000 waterfowls, mainly ducks, in the 38 infected flocks. It will further the culling if the 144 untested flocks prove to be infected with H5N1.
"What has happened in Vietnam may have public health implications for the entire world, and will be crucial in preparing for a possible pandemic," Hans Troedsson, WHO Representative in the country, was quoted in the release. <<
The above H5N1 infections appear to be in asymptomatic ducks, since there is no indication that the H5N1 positive flocks had dead or dying ducks. Moreover, the one fifth may simply reflect the fact that one fifth have been tested for bird flu. More complete testing nay generate a positive percentage significantly higher than 20%. A survey of ducks in the 11 Mekong Delta provinces earlier this season indicated that 71% of the ducks were H5N1 positive.
This report suggest H5N1 is currently widespread in Vietnam, killing chickens in the south, asymptomatically infecting ducks in the central highlands, and producing a mild disease in humans in central and northern Vietnam.
It seems likely that these outbreaks represent at least two or three versions of H5N1. Co-circulation of distinct strains of H5N1 generates dual infections by diverse genomes giving rise to more diversity via recombination.
The latest news out of northern and central Vietnam indicates that many of the earlier cases have tested positive for H5N1 via several assays, including western blot. Although these cases remain unofficial because of the confirmatory test used, it is becoming increasingly clear that the pandemic has moved to phase 6 and the mild version in humans in northern and central Vietnam could easily recombine and become significantly more lethal as the H5N1 in Vietnam continues to spread and diversify genetically.