Seroprevalence of malignant catarrhal fever in cattle and sheep from South Brazil.

Malignant Catarrhal Fever (MCF) is caused by a group of gammaherpesviruses in the genus Macavirus. The virus is transmitted via nasal shedding from adapted hosts, such as sheep, which do not develop the disease, to non-adapted hosts such as cattle, pigs, bison, and deer, which can develop an often-fatal form of the disease. There is currently no specific treatment or vaccine available to control MCF, and the resulting losses significantly affect livestock industries worldwide. To assess the seroprevalence of MCF in southern Brazil, blood samples were collected from sheep and cattle reared simultaneously on twenty farms in the western region of Rio Grande do Sul state. A competitive enzyme-linked immunosorbent assay was used to detect specific antibodies to MCF viruses, and the prevalence was calculated for each herd or flock based on the total number of samples analyzed. We found seropositive sheep in every flock evaluated, and a prevalence of 89.8%. Among cattle herds, 5.2% of the animals tested were positive. Although no clinical cases were observed during the study, the management practices used on these farms, combined with the high prevalence of seropositive sheep, represent a potentially significant risk for cattle in the region. This work provides insights into the epidemiology of MCF in southern Brazil and supports efforts to improve strategies for controlling viral transmission and disease in cattle.