First Serosurvey of Porcine Circovirus Type 3 in Central Luzon, Philippines

Porcine circovirus type 3 (PCV3) is an emerging circovirus detected worldwide in pigs with and without clinical disease, including reproductive and systemic disorders. However, baseline information on PCV3 exposure in Philippine swine populations remains limited. A cross-sectional serosurvey was conducted in selected provinces of Central Luzon, Philippines, from May to June 2025. A total of 337 serum samples from slaughter pigs were tested using an indirect enzyme-linked immunosorbent assay based on recombinant PCV3 open reading frame 2 (ORF2) capsid antigen. Samples with sample-to-positive (S/P) ratios ≥ 0.5 were classified as seropositive. Overall, 143 of 337 pigs were seropositive, corresponding to an apparent seroprevalence of 42.4% (95% confidence interval [CI]: 37.1–47.9%). Province-level apparent seroprevalence was 46.1% in Bulacan, 38.0% in Nueva Ecija, and 42.2% in Pampanga, with no significant difference among provinces (p = 0.470). However, seroprevalence differed significantly between slaughterhouses in Bulacan (66.1% in Malolos versus 27.3% in Meycauayan; p < 0.0001). These findings provide the first serological evidence of PCV3 exposure in slaughter pigs from selected provinces of Central Luzon. Because molecular testing was not performed, the results should be interpreted as evidence of an antibody response to PCV3 rather than confirmation of active infection. Expanded surveillance integrating serology, qPCR, sequencing, farm-level epidemiological data, and clinicopathological investigations is warranted.