First detection of porcine circovirus 3 (PCV3) associated with reproductive failure on a Thai pig farm

Abstract Porcine Circovirus 3 (PCV3) has been detected in pigs worldwide, including Thailand. It is associated with a range of clinical problems, including reproductive disorders, but its pathogenic role remains unclear. To date, PCV3 detection in Thailand has been reported only in pigs with respiratory signs. An outbreak of stillbirths and mummified fetuses occurred at a farrow-to-nursery farm in 2023. Clinical assessment, farm management review, and molecular testing for African swine fever virus (ASFV), porcine parvovirus (PPV1, PPV2, PPV3, PPV4, PPV5, PPV6, and PPV7), porcine reproductive and respiratory syndrome virus (PRRSV-1 and PRRSV-2), PCV2, PCV3, and PCV4 were performed. PCV3 DNA was detected in all the samples, whereas other major reproductive pathogens were not detected. A positive PCV3 sample was subjected to full-genome sequencing and phylogenetic analysis. The complete genome (2,000 nt) of this strain shares 99.35%-99.70% identity with other PCV3 strains in the GenBank database and is classified into the genotypes PCV3a1 or PCV3b, similar to previously reported strains causing reproductive disorders in other countries. No significant environmental or nutritional stressors were identified. The findings of this study provide the first molecular evidence in Thailand, suggesting that PCV3 may be the cause of reproductive failure and possible vertical transmission. PCV3 should be considered in the differential diagnosis of reproductive disorders in swine production.