Human killer let loose?

Fatal influenza virus strain found in pigs

Published: Wednesday 15 September 2004

a researcher from China's Harbin Veterinary Research Institute has recently stated that farmed pigs in some parts of the country have been infected with the h5n1 strain of the fatal avian influenza virus. The findings were presented at an international symposium on sars and avian influenza held recently in Beijing. The World Health Organization (who) has requested the researcher, Chen Hualan, to furnish further details about his study.

Pigs are known to be susceptible to infection with avian influenza viruses. However, natural infection of pigs with the h5n1 strain has not been previously reported. To assess the implications of Hualan's claim for human health, it is important to know whether the reported infection in pigs is common or not. A comparison of the h5n1 strain isolated in pigs with strains recently circulating in the poultry populations of Asia is needed to determine whether the virus is being passed directly from poultry to pigs.

Transmission of h5n1 from poultry to pigs is a matter of concern, as this increases opportunities for a new influenza virus with pandemic potential to emerge. Pigs have been implicated in the emergence of new influenza viruses responsible for two of the previous century's influenza pandemics. They have receptors in their respiratory tract that make them susceptible to infection with human and avian influenza viruses. If a pig is simultaneously infected with both human and avian influenza viruses, it can serve as a "mixing vessel", facilitating the exchange of genetic material between the two organisms in a process known as "reassortment". The resulting new virus, which will not be recognised by the human immune system, will have pandemic potential if it retains sufficient human genes to allow human-to-human transmission. Confirmation of h5n1 infection in pigs will add complexity to the epidemiology of this disease.

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