Swine influenza viruses (swIAVs) pose a significant zoonotic threat. Ongoing surveillance of swIAVs in Thailand is essential due to intensive pig farming, which promotes interspecies transmission and the emergence of novel or virulent viruses. This study aimed to conduct a multiyear survey to determine the prevalence and genetically characterize the swIAVs circulating in Thai pig populations from 2019 to 2025. A total of 1629 nasal swab samples from 21 pig farms across 11 provinces in Thailand were collected and tested for swIAV. Our results showed that 10.87% (177/1629) of the samples tested positive for swIAV using M gene‐specific real‐time RT‐PCR. Of the 177 positive samples, we successfully isolated 30 swIAVs, which were subtyped as swIAV‐H1N1 ( n = 14), swIAV‐H1N2 ( n = 3), and swIAV‐H3N2 ( n = 13). All 30 swIAVs were subsequently characterized by whole‐genome sequencing, which identified eight swIAV genotypes. Phylogenetic analysis confirmed reassortment among all subtypes (H1N1, H1N2, and H3N2). Most genes across all subtypes originated from the pandemic H1N1‐2009 (pdm) lineage, frequently reassorted with classical swine (CS), Eurasian Avian (EA), or human seasonal (HU) segments. Importantly, four new swIAV genotypes have not been reported in Thailand: endemic H1N1 (8EA), endemic H3N2 (6EA + 2HU), reassortant H1N1 (5pdm + 2EA + 1CS), and reassortant H3N2 (4pdm + 2CS + 2HU). Our results reinforced that pdmH1N1‐2009 was predominantly circulating or was introduced multiple times in pig farms, leading to various reassortments and diverse swIAV genotypes. Since endemic swIAV, pdmH1N1‐2009, and reassorted swIAVs are circulating within the pig population in Thailand, it is important to emphasize the routine monitoring of influenza viruses among pigs, farm workers, and veterinarians on pig farms. Ongoing improvements in surveillance are essential to prevent the emergence of genetically complex swIAVs with pandemic potential.
Chaiyawong et al. (Thu,) studied this question.