Comprehensive Survey of PCV2 and PCV3 in Domestic Pigs and Wild Boars Across Portugal: Prevalence, Geographical Distribution and Genetic Diversity

Porcine circoviruses are significant pathogens that affect swine populations worldwide, with implications for animal health and productivity. While PCV2 is well-documented, particularly due to widespread vaccination programs, PCV3 is less understood, and its epidemiological impact is still under investigation. This study broadly screened for PCV2 and PCV3 in pigs and wild boars across Portugal to assess their prevalence and genetic diversity. Stool samples from 160 pigs belonging to different groups (Quarantine, Nursery, Fattening, Breeding Stalls, Gestation, and Maternity), as well as organ samples from 120 wild boars, were analyzed. Samples were collected from 12 of the 18 mainland Portuguese districts with positive cases being detected in nine of them. Pigs had a lower prevalence of PCV2 (1.9%) than PCV3 (11.2%), but the opposite was true in wild boars (76.7% for PCV2 and 55.0% for PCV3). The lower PCV2 prevalence in pigs can be attributed to the PCV2 vaccination program implemented. Additionally, these viruses were significantly more prevalent in wild boars (90.8% were infected with at least one of the viruses) than in domestic pigs (only 12.5%). This significant difference highlights the impact of the controlled environment in pig farms on disease prevention in opposition to the higher exposure risks faced by wild boars in their natural habitat. Compared to our previous study from 2023, we observed a slight decrease in the percentage of positive cases for both PCV2 and PCV3. Furthermore, the positive cases detected in pigs in 2023 belonged to the PCV2d and PCV3c clades. In contrast, the samples from pigs in the present study belong to the PCV2a and PCV3c clades. Conversely, samples from wild boars belonged to the PCV2d and PCV3a clades. These results reveal genotype differences between wild and domestic pigs and shifts from 2023 to 2024. Our findings provide new insights into the circulation of these viruses and emphasize the importance of vaccination and continued monitoring for a deeper understanding of their epidemiology to mitigate potential risks to swine health and production.