Ovine gammaherpesvirus-2 associated manifestations with concomitant polioencephalomalacia, bovine alphaherpesvirus 1-related pneumonia, and caseous lymphadenitis in a sheep.

Ovine gammaherpesvirus 2 (OvGHV2), is a member of the Macavirus genus, shares the 15 A antigenic epitope that is common to members of the malignant catarrhal fever virus (MCFV) complex, and induces sheep-associated malignant catarrhal fever (SA-MCF) in susceptible mammalian hosts. Sheep, the adapted hosts, rarely show pathological evidence of infection. This study describes the unusual SA-MCF lesions in a lamb, with concomitant polioencephalomalacia (PEM), bovine alphaherpesvirus 1 (BoAHV1)-associated pneumonia, and caseous lymphadenitis. A 4-month-old, male, Santa Ines sheep died after presenting clinical manifestations of a neurological syndrome suggestive of PEM. Routine post-mortem evaluations identified rib impressions on the plural surface of the lungs, pulmonary and lymph node abscesses, and marked flattening of the cerebral gyri and narrowing of the sulci. Histopathology revealed interstitial pneumonia, suppurative bacterial bronchopneumonia, pulmonary abscesses, lymphoplasmacytic interstitial nephritis, myocarditis, and hepatitis. The brain had histological evidence of PEM. Immunohistochemistry detected intralesional intracytoplasmic antigens of MCFV within epithelial cells of the lungs, liver, kidney, and small intestine. OvGHV2 DNA was amplified from the spleen, liver, kidney, and myocardium. Other common infectious disease pathogens of sheep were not detected. Accordingly, neuropathological manifestations of PEM, with concomitant caseous lymphadenitis, and infections by BoAHV1 and OvGHV2 were diagnosed. The neurological disease is hypothesized to have disrupted the normal biological functions in this lamb, while immunosuppression caused by BoAHV1 might have reactivated a latent OvGHV2 infection. Consequently, it seems that sheep may present pathological evidence of OvGHV2-induced lesions when there is a concomitant debilitating disease condition.