Serological report of influenza a (H7N9) infections among pigs in Southern China

Background: In 2013, a novel H7N9 avian influenza virus (AIV) was isolated from ill humans in Shanghai and Anhui Province, China. Since then, the virus has spread quickly throughout China. Previous isolation of H7N2 virus from swine suggests that additional H7 subtype AIVs may be transmitted through pigs. However, prior to the recent zoonosis of H7N9, there were very few studies on the seroprevalence of the H7 subtypes in this species. Thus, there is a need to perform serological surveys for novel H7N9 as well as other H7 subtype AIVs in swine. This surveillance may help us understand risk factors for outbreaks of influenza A (H7N9) virus. Results: Only 2.0% (26/1310) of the pig sera had antibodies with an HI titer >= 1:20, and none had an MN titer >= 1:80, against the H7 antigen. Thus, no samples were found to be positive against H7N9. However, 13.6% (178/1310) of the pig sera had antibodies with HI titer >= 1:20 and 8.5% (112/1310) by MN titer >= 1:80 against H9 antigen. Thirty-seven percent (484/1310) of the pig sera had antibodies with HI titer >= 1:20 and 18.2% (238/1310) had MN titer >= 1:80 against pandemic 2009. Conclusions: Pigs in southern China have been shown to be infected with multiple avian influenza viruses. As the prevalence of novel influenza A viruses (e.g., H7N9 avian influenza virus) may be increasing among poultry in China, similar seroepidemiological studies of pigs should be conducted in the future.