A literature review and pooled data analysis were carried out to examine the prevalence of antibodies against five influenza virus subtypes in pigs in China over a 10-year period (1999-2009). The average seropositive frequencies of subtypes H1, H3, H5, H7 and H9 were 3478/11,168 (31.1%), 2900/10,139 (28.6%), 77/5945 (1.3%), 0/1440 (0%) and 86/3619 (2.4%), respectively. There was a geographical variation in the seroprevalence of subtype H1, with the highest seroprevalence in pigs in South and East China. BLAST analysis of genetic sequences revealed that genome segments with moderate homology to the 2009 pandemic influenza A (H1N1) virus were present among swine influenza viruses isolated in China, especially in South and East China. It was concluded from both serological and genetic studies that subtypes H1, H3, H5 and H9 are currently co-circulating in pigs in China, with the H1 subtype most commonly detected, followed by H3.
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