Prevalence and genetic characterization of porcine circovirus type 2, 3 and 4 in the upper Northern region of Thailand.

Porcine circovirus (PCV) poses challenges to swine health and production worldwide, with PCV2, PCV3, and may be PCV4 contributing to porcine circovirus-associated diseases (PCVAD). This study investigated the prevalence and genetic diversity of PCV2, PCV3, and PCV4 in fattening pigs from 42 farms in Chiang Mai, Lamphun, and Lampang Provinces, Thailand. A total of 396 blood samples were tested using real-time PCR, and positive samples were selected for partial capsid (cap) gene sequencing. Real-time PCR detected PCV2 in 22.73% of samples and PCV3 in 4.29%, with co-infection found in 2.78%. PCV4 was not detected. Although the Chi-square test (𝜒² = 0.937, P > 0.05) showed no significant association between PCV2 and PCV3 infections and the odds ratio for PCV2 and PCV3 infection was 1.92 (95% CI: 0.69-5.33, P > 0.05), and the relative risk (RR) was 1.85, but suggesting a potential link between PCV2 infection and increased PCV3 infection. Genetic analysis identified all PCV2-positive samples as PCV2d and PCV3-positive samples belonged to clades 3a and 3b, with geographical clustering. Lamphun samples contained only 3a, while both 3a and 3b were found in Lampang. These findings highlight the dominance of PCV2d and the need for targeted vaccination. While PCV2 vaccines are available, commercial vaccines for PCV3 and PCV4 remain unavailable, emphasizing the importance of ongoing surveillance and research for effective disease control in Thai swine farms.