Serological surveillance of H5 and H9 avian influenza A viral infections among pigs in Southern China.

Pigs are susceptible to both human and avian influenza viruses (AIV). Moreover, they are suspected of being the intermediate hosts or mixing vessels of pandemic influenza viruses. Researchers suspect that the influenza viruses are able to undergo reassortment or to adapt to various mammalian hosts while they incubate in pigs. For the present report, we conducted a serological surveillance of pigs in southern China from 2008 to 2012 to establish the prevalence of antibodies against H5N1 and H9N2 AIV. A total of one hundred pig farms from the Guangdong, Zhejiang, Fujian, and Yunnan Provinces were sampled, yielding a total of 3960 serum specimens. The haemagglutination inhibition (HI) tests revealed no evidence of H5 infection when the Clade 2.3.2 virus was used as the antigen, but a 4.6% positive rate of H9 infection was observed when using the Beijing/1/94-like virus as the antigen. The positive sera for H9 infection were further verified with neutralization tests, which confirmed a 3.7% rate of positive sera of H9 infection. In summary, the results imply that the swine populations in southern China had not been affected greatly by the H5N1 avian influenza virus. Nevertheless, these swine H9N2 influenza viruses might pose a threat to human health, and so researchers should continue to carry out swine influenza virus surveillance in China.