Evidence of Spillover and Recombination Between Domestic Pigs and Wild Boars Provides New Insights into Porcine Circoviruses.

Porcine circovirus types 2 (PCV2) and 3 (PCV3) are major pathogens affecting swine health and productivity, yet important gaps remain in understanding their evolution and circulation in Europe, particularly within wild boar populations that may serve as reservoirs. This study examined the genetic diversity and evolutionary dynamics of PCV2 and PCV3 in Portugal, drawing on viral genomes obtained from domestic pigs and wild boars to explore transmission patterns, spillover events and the contribution of recombination to viral emergence. We identified two PCV2 genotypes (PCV2a and PCV2d) and two PCV3 genotypes (PCV3-2a and PCV3-3g) circulating in Portuguese swine. Phylogeographic reconstruction revealed multiple introductions of both PCV2 and PCV3 from China into Europe, followed by regional diversification and subsequent spread within European wild boar populations. Evidence of bidirectional viral exchange between domestic pigs and wild boars was also observed. Recombination played a notable role in PCV2 evolution, with consistent signals detected among PCV2a sequences and indications that the PCV2h genotype likely originated from a recombinant event involving a Portuguese PCV2a strain and a Chinese PCV2d strain. By contrast, no recombination was detected in PCV3, suggesting that its evolution is primarily mutation-driven. Overall, these findings highlight the complex evolutionary history of swine circoviruses in Europe and underscore the importance of continuous genomic surveillance in both domestic and wild hosts. The study reinforces the value of a One Health approach for monitoring and controlling emerging circoviruses with implications for animal health and livestock production.