Zeller et al. collected more than 4,000 nasal swabs from pigs in Cambodia between March 2020 and July 2022; the authors then performed whole-genome sequencing and evolutionary and phylogeographic analyses to explore virus strains and spread. The H1N1 subtype was present in 80% of samples. European avian-like (EA) H1N2 reassortant genotypes were generated through the intercontinental movement of different viral lineages, and China was the leading source contributing to dissemination of EA swine viruses in Asia. Diverse lineages of H1 were in circulation within Cambodia, with the majority of the new H1 and N1 sequences derived from the human H1N1/pdm09 lineage, suggesting that human-to-swine transmission occurred as early as August 2017, followed by enzootic spread of a genetically distinct H1N1/pdm09 sublineage among pigs in Cambodia. Modelling studies suggested that pork production at origin was positively correlated to the spatial spread of EA H1N1 swIAV. By contrast, the consumption of pork in both origin and destination regions was negatively correlated with virus spread.
Global swine populations provide a suitable environment for reassortment and human adaptation of avian and mammalian influenza viruses that can contribute to the emergence of zoonotic influenza and pandemic viruses. Zeller et al. show an increasingly complex genomic landscape of swIAV in Southeast Asia that is shaped by repeated introduction and reassortment of virus lineages, a process that is known to heighten pandemic risk. As demand for pork in the region grows, genomic surveillance at the human–swine interface will become increasingly important for early warning of disease emergence — and to avoid future pandemics.
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