For the first time a new study suggests that when exposed in their natural ecosystem, wild pikas (a species closely related to rabbits) are mammalian hosts of H5N1 subtype avian influenza viruses and may also be a source of transmission to domestic mammals and humans.
The researchers from China report their findings in the September 2009 issue of the Journal of Virology.
Wild birds are the known natural reservoirs for the H5N1 subtype avian influenza virus, however, researchers are unsure of their role in the spread of the virus to other free-ranging wild mammals within their natural habitats. Highly pathogenic H5N1 avian influenza viruses are now endemic in bird populations throughout Southeast Asia and 391 human cases, of which 60% were fatal, have been reported since 2003. Although human-to-human transmission has yet to occur, H5N1 viruses pose a serious public heath threat.
In the study researchers traced the circulation of the H5N1 virus in wild pikas and confirmed a natural H5N1 virus infection in their native environment. Genetic testing of the H5N1 virus isolated in pikas revealed two distinct evolutionary groups, a mixed/Vietnam H5N1 virus sublineage (MV-like pika virus) and a wild bird Qinghai-like H5N1 sublineage (QH-like pika virus). Further analysis of the MV-like pika virus found it to be the same as goose H5N1 virus. When tested in mice the MV-like pika virus was nonpathogenic, however, the QH-like pika virus was highly pathogenic in mice. Finally, in an attempt to recreate the virus infection of pikas, rabbits were intranasally vaccinated with the H5N1 virus of pika origin resulting in infection.
"Our findings first demonstrate that wild pikas are mammalian hosts exposed to H5N1 subtype avian influenza viruses in the natural ecosystem and also imply a potential transmission of highly pathogenic avian influenza virus from wild mammals into domestic mammalian hosts and humans," say the researchers.
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