Molecular and histopathological characterization of sheep-associated malignant catarrhal fever (SA-MCF) outbreak in beef cattle.

An outbreak of suspected malignant catarrhal fever (MCF) was investigated by molecular and histopathological assays. Of the 70 Holstein beef calf herds, 14 were affected by multiple clinical signs suggestive of MCF infection. These beef calves were housed next to sheep flocks. In the complete blood count, the 14 affected calves had severe anaemia with leucopaenia, lymphopaenia and neutropaenia. Upon PCR amplification using a hemi-nested PCR assay for the detection of the Ovine herpesvirus 2 (OvHV-2), bovine tissue samples from the mesenteric lymph nodes and spleen and ovine blood samples were shown to be positive with the expected PCR bands amplified. Direct sequencing of the hemi-nested PCR product confirmed the identity of the causative virus as OvHV-2. The histopathological findings confirmed the clinical and laboratory diagnosis of MCF. Collective clinical, PCR and histopathological data confirmed the identity of this outbreak to be a sheep-associated malignant catarrhal fever (SA-MCF).