Caprine arthritis-encephalitis: clinicopathologic study.

Chronic arthritis caused by caprine arthritis-encephalitis virus was observed after the introduction of new animals into a goat herd. There were high frequency of carpal hygroma and clinical signs of stiffness. The disease was progressive and produced a debilitating lameness among 30% of the affected animals. Laboratory findings were limited to alterations in synovial fluid which showed increased numbers of lymphocytes. Pathologic changes were observed in the joints, bursae, and adjacent tissues. Vascular injury and capillary leakage resulted in exudation into synovial cavities. Fibrin coated the synovial lining and formed (amorphous) long thread-like or broad-based villi. The articular cartilage was eroded. Cartilage erosion and penetration of the articular cartilage by pannus were associated with the presence of subchondral pseudocysts. The morphologic changes in bone and synovial tissues were like those described in human rheumatoid arthritis, except that rheumatoid nodules were not observed.