Serological Evidence of Co-Circulation of Different Subtypes of Swine Influenza Virus in Polish Pig Herds

The aim of the study was to estimate the current epidemiological situation concerning swine influenza (SI) in Poland. The study was based on an annual passive survey of 11,770 fatteners’ sera from 584 herds, taken at slaughterhouses within the last 30 months (from January 2010 till June 2012), as well as, an active monitoring conducted in 2011 and 2012, in 25 farms, using 388 sera taken from life pigs of different age/technological groups. The analysis of simultaneous circulation of different swine influenza virus (SIV) subtypes was taken into a deep consideration. The wide spread of SIV in Poland, including the occurrence of multiple SIV infections was demonstrated. In 2010 and 2011, the domination of H1N1 subtype and the most frequently co-circulation of H1N1 and H1N2 viruses was evidenced, while in the first 6 months of 2012, the co-circulation of H1N1 and H3N2 viruses was detected more often. Based on the obtained results, it can be stated that the epidemiological situation concerning SI in Poland is dynamic and similar to that observed in other European regions with high pigs’ density; however, the prevalence of antibodies and the occurrence of mixed SIV infections is lower than in Western Europe.