Human-Origin Influenza A(H3N2) Viruses Revealed in Swine Farms During the Period 2022-2025 in Kazakhstan

Seasonal human influenza A viruses (H1N1 and H3N2) are frequently transmitted to swine populations. Continued transmission of these viruses among swine results in genetic and phenotypic changes, creating new lineages of swine influenza viruses that differ from their parent strains. This contributes to increased viral genetic diversity and the emergence of zoonotic risks. The aim of this study was to assess the prevalence of influenza viruses, including presumably human-origin A(H3N2) strains, on swine farms in Kazakhstan from 2022 to 2025. Real-time RT-PCR was used to test nasal swab antigens, and hemagglutinin inhibition test, and ELISA were used to determine serum antibody levels. Influenza A/H1N1 and A/H3N2 viruses, as well as the A(H7) hemagglutinin genes, were detected in swine. Serological analysis confirmed the presence of antibodies to the A/H1N1pdm09 and A/H3N2 viruses. The influenza A(H3N2) isolates were found to be genetically similar to human viruses of the J.2 or 3C.2a1b.2a.2a.3a.1 clade, possibly indicating transmission from humans to animals. The ongoing exchange of influenza viruses between humans and swine poses a threat of future pandemics. These studies highlight the need for continuous monitoring of swine influenza in Kazakhstan to understand virus evolution and protect public health.