Swine Influenza a Virus (SWIAV) Seroprevalence in Macedonian Commercial Farrow-to-Finish Pig Farms

Swine influenza caused by the influenza A virus significantly affects pig production and pig health due to acute respiratory disease and huge economic losses. Pigs play an essential role in the epidemiology of influenza because they act as a mixing vessel for the formation of potentially pandemic zoonotic strains. The objective of our study was to assess the seroprevalence of Swine influenza A viruses (swIAV) in commercial pig farms in Macedonia. A total of 373 blood samples were collected from piglets aged 1 to 4 weeks of sows with different parities from 19 different commercial farrow-to-finish pig farms. For the detection of anti-IAV antibodies, sera samples were analyzed using a competitive ELISA. All farms were seropositive to swIAV. Seropositivity was detected in 258 (69.2%) samples, ranging between 10 and 100% at farm level. The highest seroprevalence was found in piglets from sows in 5-6^th parity. In contrast, the lowest seropositivity was found in samples from the youngest sows (1-2^nd parity), which indicates that the virus has circulated for a longer period in these farms. Furthermore, large farms with more than 120 sows had a significantly greater percentage of seropositive animals than small farms with less than 120 breeding sows (83% vs. 54%, respectively). In conclusion, our results demonstrated that swIAV circulates endemically in Macedonian commercial farrow-to-finish pig farms, underscoring the need of immunization in preventing infection on these farms.