INTRODUCTION: Sheep associated-malignant catarrhal fever is a frequently fatal, lymphoproliferative, and vascular disease caused by ovine gammaherpesvirus 2 (OvGHV2), a member of the malignant catarrhal fever virus (MCFV) complex. OvGHV2-related epidemics normally have reduced morbidity with elevated lethality. METHODOLOGY: This study investigated the causes of elevated morbidity, mortality, and lethality in cattle maintained on Brachiaria grass pastures and with neurological and enteric disease syndromes from nine farms in Paraná, Southern Brazil. RESULTS: The principal histopathological findings included necrotizing lymphocytic vasculitis, proliferative vascular lesions, and toxic cholangiohepatitis. An immunohistochemical (IHC) assay utilizing the 15A monoclonal antibody (15A-MAb), which is specific for MCFV, revealed positive intracytoplasmic immunoreactivity within the epithelial cells of the lungs, intestine, liver, and kidneys in most animals, confirming infections by MCFV. PCR detected singular infections by OvGHV2 (n = 3) and bovine gammaherpesvirus 6 BoGHV6 (n = 3) in cattle with positive intracytoplasmic immunoreactivity by the 15A-MAb IHC assay. In one animal with positive immunoreactivity to the 15A-MAb IHC assay, neither Macavirus was identified through molecular testing. CONCLUSIONS: These findings suggested that these two Macavirus were associated with the positive IHC findings. Additionally, the non-detection of OvGHV2 and BoGHV6 in the organs of one animal, despite typical vascular lesions and with positive IHC results, suggests that another Macavirus may be involved. Moreover, the identification of BoGHV6 DNA in cattle not infected by OvGHV2 but containing MCFV antigens, indicates cross-reactivity of BoGHV6 with the 15A-MAb assay. The possibe role of Bracharia on the occurrence of these infections is discussed.