Flu: no sign so far that the human pandemic is spread by pigs

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Sir

Further to your Editorial 'Animal farm: pig in the middle' (Nature 459, 889; 2009), the World Organisation for Animal Health (OIE) would like to clarify what is understood so far about how animals are associated with the human influenza A/H1N1 pandemic.

Although the human H1N1 virus contains gene sequences that have been identified in influenza viruses from swine, these are not present in exactly the same combination. The OIE has encouraged its members to intensify surveillance of pigs for infection, but there has been no evidence so far that swine are playing any role in the epidemiology or in the worldwide spread of the virus in the human population. It is likely that we shall never know the specific origin of this pandemic virus.

As you mention, the OIE has campaigned against calling the human disease 'swine flu'. Although the World Health Organization (WHO), the UN Food and Agriculture Organization (FAO) and the OIE have since agreed officially to rename the virus 'pandemic (H1N1) 2009', common use of the misleading term 'swine flu' is in danger of continuing. This initially prompted several countries to ban import of pigs and pig products or to destroy all their pig populations, without any benefit to public or animal health. It could cause further economic harm, in the same way that the H5N1 'avian flu' crisis of 2004 unnecessarily triggered a drop in people's consumption of poultry products. Such an unjustified disruption of trade would affect small farmers and animal producers around the world, more than a billion of whom are already living in poverty.

In 2005, the FAO and OIE set up a joint network of expertise on animal influenza. The network, OFFLU, was created to help the WHO obtain rapid access to circulating animal viruses for the early preparation of human vaccines. After the emergence of the pandemic virus in humans, OFFLU called for laboratories worldwide to aid public health by publicly sharing gene sequences of influenza virus identified in swine. As a result, it is proposed to expand the current OIE reference laboratories for avian influenza to cover all animal influenza viruses and to increase research on the behaviour of these viruses at the human–animal interface.

The OIE will continue to advise its members and the public on the control of potential zoonotic diseases, for example by strengthening veterinary infrastructure and stepping up surveillance and reporting capabilities in all countries, regardless of their trade potential.

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Vallat, B. Flu: no sign so far that the human pandemic is spread by pigs. Nature 460, 683 (2009) doi:10.1038/460683b

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