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H5N1 Infections In Japanese Farm Workers
December 23, 2004
>>The data demonstrate that exposure to avian influenza virus-infected
poultry does not pose a serious risk to human health.<<
The above comment should be extensively modified to reflect the true nature of the posted data. Although five workers had antibody against A/chicken/Kyoto/3/2004(H5N1), a titer of >10 is not a very convincing number, (patients exposed to the 1918 pandemic virus had higher titers 85 years after exposure) and indeed only 1 of the 5 workers was tested twice to show a rising titer.
Since the positives were involved in decontaminating an H5N1 infected farm over an extended time period, the titer may in fact represent antibody to killed virus, since no virus was isolated from any of the "infected" workers.
However, even if the workers were infected with A/chicken/Kyoto/3/2004(H5N1) or a closely related virus, the failure of the virus to produce serious illness in these workers would not indicate that "exposure to influenza virus-infected poultry does not pose a serious risk to human health".
The H5N1 isolates in Vietnam and Thailand are associated with a case fatality rate in excess of 70%. Although the sequences of the isolates from Japan have not been made public, full sequences from a large number of 2004 H5N1 isolates in Thailand and Vietnam have been published and these isolates (from humans, wild cats, and a variety of wild and domestic poultry) have polymorphisms specific for Vietnam, Thailand, or both countries. Many of the polymorphisms are not found in other H5N1 isolates, but in fact are found in mammalian isolates, most notably H1N2.
The above Kyoto virus is described in a MAFF report dated 6/30/2004. The table on page 26 appears to show the homology between a representative Kyoto isolate and a number of other H5N1 isolates (Ck/Korea/ES/03, Dk/China/E319-2/03, Dk/Anyang/AVL-1/01, Thailand/KAN-1/04, Ck/Supanburi/2/04, Dk/Angthong/72/04, Qa/Angthong/72/04, Vietnam/1096/04, HK/213/03, Ck/HK/YU562/01, HK/156/97).
All 8 genes are listed and a full data set is listed for most isolates. The isolate from Korea is 99% homologous for all 8 genes. The percent homology is considerably lower for other isolated. For HA and NA of the Thailand and Vietnam isolates, the percent homology is 96% and 97% respectively for HA and NA. Thus, there are considerable differences between the isolates from Japan and the isolates from Vietnam or Thailand.
Extrapolating weak antibody data from a small number of farm workers with repeated exposure to killed virus to exposure to avian influenza infected poultry is not justified because of the publicly available sequence and case fatality data from Vietnam and Thailand H5N1 infected people and animals.
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H5N1 "Infections" in Japanese Farm Worker(s)