Original Scientific Article 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 5-6th parity. In contrast, the lowest seropositivity was found in samples from the youngest sows (1-2nd 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. https://macvetrev.mk/LoadArticlePdf/417 2025-07-24 i ix https://doi.org/10.2478/macvetrev-2025-0025 Swine influenza A virus seroprevalence pigs commercial farms Macedonian Branko Angjelovski false 1 Department of Farm Animals Internal Medicine, Faculty of Veterinary Medicine-Skopje, Ss. Cyril and Methodius University, Lazar Pop-Trajkov 5-7, 1000 Skopje, N. Macedonia AUTHOR Miroslav Kjosevski false 2 Department of Animal Hygiene and Environmental Protection, Faculty of Veterinary Medicine-Skopje, Ss. Cyril and Methodius University, Lazar Pop-Trajkov 5-7, 1000 Skopje, N. Macedonia AUTHOR Aleksandar Janevski false 3 Department of Pathology and Forensic Veterinary Medicine, Faculty of Veterinary Medicine-Skopje, Ss. Cyril and Methodius University, Lazar Pop-Trajkov 5-7, 1000 Skopje, N. Macedonia AUTHOR Jovan A. Bojkovski false 4 Department of Ruminants and Swine Diseases, Faculty of Veterinary Medicine, University of Belgrade, 11000 Belgrade, Republic of Serbia AUTHOR Aleksandar Dodovski false 5 Department of Avian Diseases, Faculty of Veterinary Medicine-Skopje, Ss. Cyril and Methodius University, Lazar Pop-Trajkov 5-7, 1000 Skopje, N. Macedonia AUTHOR Er, C., Skjerve, E., Brun, E., Hofmo, P.O., Framstad, T., Lium, B. (2016). Production impact of influenza A(H1N1) pdm09 virus infection on fattening pigs in Norway. 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