A review of the epidemiological, clinical, and pathological aspects of malignant catarrhal fever in Brazil.

Sheep-associated malignant catarrhal fever (SA-MCF), the form of MCF that occurs in Brazil, is a severe, frequently fatal, infectious disease caused by ovine gammaherpesvirus-2 (OvHV-2), in which sheep are the asymptomatic hosts and cattle and other cloven-hoofed animals are the accidental hosts. This review provides a critical analysis of the historical, epidemiological aspects and the estimated economic impacts associated with SA-MCF in Brazil. Moreover, the clinical manifestations and pathological lesions associated with SA-MCF in cattle are reviewed and discussed and the phylogenetic distribution of OvHV-2 in Brazil is presented. OvHV-2 is the only MCF virus identified in animals from Brazil. It is recommended that a histopathologic diagnosis of SA-MCF be based on all aspects of vascular disease in the affected animal and not only lymphocytic/necrotizing vasculitis and/or fibrinoid change. Conformation of the intralesional participation of OvHV-2 in these alterations can be achieved by immunohistochemistry and/or in situ hybridization assays. Additionally, it is proposed that OvHV-2 should be considered as a possible infectious disease agent associated with the development of bovine respiratory disease in cattle. Furthermore, the possible role of the small intestine in the dissemination of OvHV-2 is discussed.