Diclazuril treatment ineffective at preventing Equine Protozoal Myeloencephalitis relapse in established mouse model.

Abstract

The debilitating and potentially fatal neurologic disease, Equine Protozoal Myoencephalitis (EPM), is one of the most common neurologic diseases seen in the equine population of the United States. Disease develops as a result of unintentional ingestion of the pathogenic parasite, Sarcocystis neurona. Treatment options consist of the anticoccidial drug Diclazuril and numerous other antiprotozoal drugs. Weeks to months after cessation of antiprotozoal drug treatment and corresponding neurologic improvement, horses may present with clinical disease symptoms again. Little is known whether this reoccurrence of symptoms is from relapse or reinfection. We sought to understand if relapse was possible following appropriate treatment with diclazuril, a commonly used medication for the treatment of EPM. Using a mouse model of equine EPM, we subjected infected mice to treatment with or without diclazuril for 30 and 60 days. All untreated mice developed neurologic symptoms consistent with S. neurona infection within 30 days post infection. All diclazuril treated mice developed neurologic symptoms cessation of treatment. Cerebellum samples were examined for lesions characteristic of those associated with S. neurona infection and immunohistochemically for presences S. neurona. Sera immunoglobulin levels were analyzed to evaluate treatment’s effect on humoral immunity. In conclusion horses treated appropriately with 60 days of diclazuril may be at risk for relapse and more effective treatment options should be explored.