Determination of the activity of pyrimethamine, trimethoprim, sulfonamides, and combinations of pyrimethamine and sulfonamides against Sarcocystis neurona in cell cultures

Equine protozoal myeloencephalitis (EPM) is a neurologic syndrome in horses from the Americas and is usually caused by infection with the apicomplexan parasite, Sarcocystis neurona. The activities of pyrimethamine, trimethopr im, sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfamethoxazole , sulfamethazine, and sulfathiazole were examined against developing S. neu rona merozoites in bovine turbinate cell cultures. A microtiter plate host cell lesion based assay was used to determine the effects of agents on deve loping merozoites. A cell culture flask assay was used to determine if sele ctive concentrations of the agents killed or only inhibited development of S. neurona. Pyrimethamine was coccidiocidal at 1.0 mu g/ml and trimethoprim was coccidiocidal at 5.0 mu g/ml. None of the sulfonamides had activity wh en used alone at 50.0 or 100.0 mu g/ml. Combinations of sulfonamides (5.0 o r 10.0 mu g/ml) with 0.1 mu g/ml pyrimethamine demonstrated improved activi ty. (C) 1999 Elsevier Science B.V. All rights reserved.