Naturally Occurring Sheep-Associated Malignant Catarrhal Fever in North American Pigs

Two cases of sheep-associated malignant catarrhal fever (MCF) in pigs were diagnosed on a small farm in New York, and in Kentucky. In both cases, the initial diagnosis was based on histopathological changes representing typical lymphoproliferative vasculitis in multiple tissues of the affected pigs. Ovine herpesvirus 2 (OvHV-2) DNA was detected by polymerase chain reaction in the tissues of affected pigs in both cases. The amplified sequences were identical between the clinically affected pigs and the OvHV-2-infected sheep. Additional virological and bacteriological examination showed that the affected pigs were negative for agents that cause Aujeszky's disease, classical swine fever, porcine enterovirus, and rabies. An antibody against a conserved epitope among MCF viruses was detected in 1 clinically affected pig and 2 unaffected cohort pigs, as well as in all the associated sheep. To the authors' knowledge, this is the first report of porcine MCF in North America, and suggests that OvHV-2 is associated with clinical MCF in pigs.