Pathological, immunohistochemical, and molecular findings of equine protozoal myeloencephalitis due toSarcocystis neuronainfection in Brazilian horses

Equine protozoal myeloencephalitis (EPM) is an important neurologic disease of horses in the American continent caused bySarcocystis neuronaandNeospora hughesiinfection. This study describes the pathological, immunohistochemical, and molecular findings of fatal cases of EPM in southern Brazil. A review was performed on a total of 13 cases compatible with EPM, which were diagnosed by postmortem examination in the period of 2010-2017. Epidemiological information was obtained from necropsy reports. Gross and histological lesions were characterized, and cases were subjected to immunohistochemistry anti-Sarcocystis neurona,Toxoplasma gondii, andNeosporaspp. Molecular search was performed using ITS-1 gene PCRs. Microscopic lesions were multifocal in all cases, and more frequently observed in the spinal cord segments and in the rhombencephalon. Intralesional protozoans were histologically detected in five horses, while a positive immunostaining forS. neuronawas observed in eleven cases (11/13). Through molecular techniques, six positive cases for the ITS-1 gene were detected, and obtained sequences presented highest similarity withS. neurona. EPM due toS. neuronainfection represents an important neurologic disease of horses in Brazil and this disease should be considered as a main differential diagnosis in horses presenting neurologic signs.