Efficacy of ponazuril 15% oral paste as a treatment for equine protozoal myeloencephalitis.

Equine protozoal myeloencephalitis (EPM) is a neurologic disease of horses most commonly caused by the protozoan parasite Sarcocystis neurona. Until recently the only treatment option was the combination of a sulfonamide with pyrimethamine. The present study was performed to assess the efficacy of ponazuril, an anticoccidial triazine-based compound, as a treatment for naturally occurring EPM. One hundred one horses with EPM were randomly allocated to treatment with ponazuril 15% oral paste at either 5 or 10 mg/kg body weight for 28 consecutive days. Horses were evaluated clinically and by analysis of blood and cerebrospinal fluid (CSF) before and 28 and 118 days after the start of treatment. Clinical success was defined as either an improvement in neurologic score by at least one grade (on a 0 to 5 scale) or conversion to negative status on Western blot for S. neurona antibodies by 90 days following cessation of treatment. Overall, 62% of the horses, including 28 of 47 treated with ponazuril at 5 mg/kg and 35 of 54 treated with 10 mg/kg, met the criteria for successful treatment. The Western blot for CSF became negative in 10% (10/101) of the horses. Quantification of the anti-17kDa antibody response in Western blot (relative quantity CSF) did not reveal a significant change in response to treatment. However, immunoglobulin index did decrease significantly during treatment (P = .01). The findings of this study support the efficacy of ponazuril for the treatment of EPM.