Concurrent histological lesions and molecular detection of porcine circovirus 3 in pigs with skeletal abnormalities and humpy-back posture

Porcine circovirus 3 (PCV-3) is associated with various pathological conditions, including systemic disease and reproductive disorders; however, its role in skeletal abnormalities has never been elucidated. This study included 36 cases displaying spinal malformations, rib swelling, head edema, gait abnormalities, and/or increased late-term abortions. Investigated animals consisted of 9 aborted fetuses, 9 piglets, 12 weaners, and 6 finishers. Histologically, PCV-3 associated lesions were identified in 23/36 cases (64%), including (peri-)arteritis and rib fractures with prominent callus formation. Central nervous system (CNS) lesions, in addition to vascular changes, comprised meningoencephalitis and gliosis. Thirteen animals (36%) did not display histological lesions. PCV-3 DNA was detected by real-time PCR (qPCR) in 25/36 animals (69%), with high viral loads in the bone and CNS. Three aborted fetuses tested positive for PCV-3 despite lacking macroscopic and histologic lesions. <i>In situ</i> hybridization (ISH) revealed the presence of PCV-3 RNA in multiple organs, including arteries, the heart, CNS, and bone. Signals were detected in periosteal arteries and osteoblasts, within calluses, and in arteries within the surrounding skeletal muscles. This study strengthens the association between PCV-3 and multisystemic inflammatory diseases, expanding its known pathogenicity to include skeletal lesions and spinal deformities. It is the first documentation of PCV-3 genome in histologically altered bone. This finding could suggest a possible etiological role in musculoskeletal abnormalities. In addition, this study is the first to report PCV-3-associated lesions in slaughter-ready finisher pigs. The integration of histological investigations, PCR, and ISH techniques is essential for the diagnosis of PCV-3-associated diseases and related lesions.