IMMUNOHISTOCHEMICAL STUDY TO DEMONSTRATE SARCOCYSTIS-NEURONA IN EQUINE PROTOZOAL MYELOENCEPHALITIS

A 5-year (1985-1989) retrospective immunohistochemical study was condu cted using an avidin-biotin complex (ABC) immunoperoxidase method to d emonstrate Sarcocystis neurona in histologically suspect cases of equi ne protozoal myeloencephalitis (EPM). Primary antibodies against S. ne urona and S cruzi were utilized for the ABC technique. The findings we re compared with those from cases in which the organisms were detected by examination of hematoxylin and eosin (HE)-stained neuronal section s. HE-stained sections detected the presence of the organisms in 20% o f the suspect cases; whereas the ABC technique confirmed the presence of S. neurona in 51% and 67% of the cases by S. neurona and S. cruzi a ntibodies, respectively. A review of clinical case histories showed th at 21/47 (45%) of the EPM horses with parasites in the tissue sections had prior treatment with antiprotozoal drugs and/or steroids. Using t he test results of S. neurona and S. cruzi as a standard reference, HE test sensitivity based on examination of up to 30 neuronal sections p er case was only 25%, and test specificity was 91%.