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H7N3 in Vietnam
December 24, 2007
The dangerous, human-transmissible avian influenza A (H7N3) strain, previously recorded in Korea, Canada and Holland, has reemerged in several Asian countries including Vietnam, according to the National Steering Committee for Avian Influenza Prevention and Control.
The H7N3 virus found in Vietnam, however, is classified as low-pathogenic, not readily transmitted to humans.
The above comments on the emergence of H7N3 in Vietnam, coupled with the media myth of poor human transmission, are cause for concern. H7 is readily transmitted to humans, although assays for H7 are poor. The most extensive documented transmission to humans was during the H7N7 outbreak in the Netherlands in 2003. Initially, over 80 cullers were reported to be infected with H7N7. Most infections were mild, but one veterinarian died. The death is the only avian influenza human death reported that was not H5N1. However, a follow-up study on antibodies in contacts of the cullers indicated that over 1000 people were infected.
Although the Netherlands outbreak was high path, human cases have been reported in most H7 outbreaks. The most recent was the H7N2 outbreak in England, where there were more suspect human cases than avian cases even though the H7N2 was low path. The final count of human cases in England remains confused. At a “Breaker” session at the Options VI meeting in Toronto in June, the spread of the H7N2 in humans was described. Although this outbreak was in the summer, when monitoring should have been facilitated by the low level of seasonal flu, the report in Toronto was far from complete. A more finalized version of the human cases was promised, but there has been no such report in the past six months.
Recently, H7N3 avian influenza was reported in Saskatchewan, Canada and H7N8 was reported in South Korea. The H7N8 bird flu outbreak in South Korea was also low path, but there was little information on human cases. In the past North Korea reported an H7 infection, but no information was forthcoming on the N serotype.
The co-circulation of H7 and H5 is cause for concern. H5 has a high case fatality rate, but low transmission. H7 has a high transmission rate but a low case fatality rate. Co-circulation can lead to co-infections and exchange of genetic information between H7 and H5 via reassortment or recombination.
More information on the H7N3 outbreak in Vietnam would be useful, along with monitoring of H7N8 contacts in South Korea.
Recombinomics Paper at Nature Precedings