Clinical, pathological, and molecular aspects of malignant catarrhal fever in Russia: a case report.

Malignant catarrhal fever (MCF) is a highly fatal viral disease caused by ovine gammaherpesvirus-2 (OvHV-2) that primarily affects cattle around the world. Sheep act as asymptomatic carriers, silently perpetuating the virus. Despite its global presence, MCF remains poorly understood in Russia due to limited surveillance, voluntary disease reporting, and its exclusion from routine differential diagnoses. This study aimed to investigate a suspected case of MCF in a Yakut-breed cow on a private farm in Pskov Oblast, Russia, bordering Estonia. The cow resided in a mixed sheep and cattle herd with direct sheep contact. Clinical examination and histological analysis revealed characteristic MCF lesions. Phylogenetic analysis of the cow's OvHV-2 revealed a mosaic structure. The polymerase01, gene clustered with strains from the Netherlands and Germany, while the tegument gene grouped with isolates from India and Egypt. This highlights the global nature of OvHV-2 genetic diversity. Overall, this study provides the first documented case of MCF in Russia and underscores the sporadic nature of the disease in cattle. The identification of novel pathological changes and the unique viral genetic makeup necessitate further investigation of MCF in Russia.