Swine influenza virus surveillance programme pilot to assess the risk for animal and public health, the Netherlands, 2022 to 2023.

BackgroundSwine influenza has a considerable impact on pig populations and poses a pandemic threat to humans. However, little is known about the influenza A viruses circulating among pigs in the Netherlands.AimWe piloted a surveillance programme aimed at enabling swine influenza A virus (swIAV) surveillance in the Netherlands: investigated prevalence, genomic characteristics and recent evolution of circulating swIAV variants and compared them with relevant human and swine influenza viruses from the Netherlands and other European countries.MethodsWe collected and tested respiratory samples from pigs (2019-2023) for swIAV, characterised the viruses with molecular and virological methods and shared molecular data of swine and relevant human influenza A viruses in a national platform.ResultsWe detected swIAV throughout the year in 342 (42%) of 824 respiratory samples from 90 farms. Complete genome sequencing identified 73 H1N1, 51 H1N2 and one H3N2 viruses. Phylogenetic analyses identified viruses from each of the three H1 swine lineages (1A/B/C) and four subclades. Viruses from the 1A lineage clustered into three subgroups with distinct antigenic properties, which seemed descendent from separate introductions of human seasonal A(H1N1)pdm09 viruses. Phenotypically, no reduced susceptibility to existing antiviral drugs oseltamivir and zanamivir was found.ConclusionWe provided insights into swIAVs in pigs in the Netherlands, including antiviral susceptibility and antigenic differences. It highlighted occasional virus transmission between humans and pigs. Sharing swIAV data at a national level will be continued to reduce influenza burden in swine and support identification and characterisation of emerging swIAVs with zoonotic potential.