Serological study and genetic characterization of swine influenza virus in four high pig density provinces in Thailand between 2006-2009

Abstract

Swine influenza is an acute respiratory disease in pigs caused by type A influenza viruses. Swine influenza virus (SIV) infection causes acute respiratory syndrome leading to economic loss. Moreover, swine may act as a ‘Mixing vessel’ and transmit a reassorted virus back to humans or vice versa similar to the pandemic influenza 2009. Importantly, both virological and serological investigation of influenza A virus in pigs will provide a better understanding of the epidemiology, epidemic prediction and vaccine development leading to effective control and prevention of the disease in both swine and humans. Genetic characterization of Thai SIV subtype H1N1 and H1N2 during 2005-2010 were evaluated and found that at least 2 clusters were identified in each subtype. Then, the antigenic property was evaluated using hyper-immune rabbit sera as positive controls tested by HI. Later, serology study of H1 and H3 Thai SIV using swine serum in the top 4 pig density provinces in 2008-2009 in Thailand demonstrating that over 50% had seropositive to H1 and H3. Moreover, pig-to-human transmission was demonstrated on Thai swine farms and swine exposed population had over 40 times likely being infected by SIV. Finally, co-circulation of pandemic (H1N1) 2009 and seasonal swine H1N1 viruses were found in a commercial pig farm. The result showed increase SIV circulation containing genetic variation with a mix combination of the North American and European lineages.