An outbreak of porcine malignant catarrhal fever in a farrow-to-finish swine farm in the United States

Malignant catarrhal fever is a sporadic, often fatal viral disease affecting multiple species, including swine. Ovine herpesvirus type 2 (OvHV-2), the cause of sheep-associated malignant catarrhal fever, incites nonspecific clinical signs and occasional death in swine. An outbreak of malignant catarrhal fever in a farrow-to-finish swine farm in the United States was confirmed by identifying OvHV-2 DNA in two clinically affected adult swine previously exposed to sheep. Forty-one swine exhibited clinical signs of lethargy, anorexia, and fever, with recovery or death in 22 and 19 animals, respectively. Abortion was also reported in two clinically affected pregnant females. Ovine herpesvirus type 2 DNA was identified by polymerase chain reaction (PCR) in spleen, brain, and lung tissue. A BLAST homology search of the sequenced PCR amplicon matched the conserved region of the OvHV-2 tegument protein. Porcine malignant catarrhal fever is difficult to diagnose due to the nonspecific clinical signs, rarity of occurrence, and sporadic nature of the disease. Polymerase chain reaction assays and serologic testing are available to assist in an accurate diagnosis. Veterinarians should consider malignant catarrhal fever a potential differential diagnosis in swine with poorly defined clinical signs, intermittent death, and previous exposure to sheep.