Therapeutics for Equine Protozoal Myeloencephalitis


Key points

  • Equine protozoal myeloencephalitis (EPM) is a diagnosis of exclusion and relies on the presence of neurologic signs, ruling out other neurologic disorders, and the detection of antibodies to Sarcocystis neurona or Neospora hughesi in serum and cerebrospinal fluid using quantitative immunodiagnostic tests.

  • Three treatment formulations approved by the US Food and Drug Administration are commercially available for the treatment of EPM and these formulations are broadly equivalent in therapeutic efficacy. Two of these formulations are specifically antiapicomplexan and a positive response to these agents strongly supports an EPM diagnosis. Treatment should be continued until no further clinical improvement is observed. Relapse following cessation of treatment may occur in a percentage of cases and is not an insignificant clinical problem.

  • Nonempiric treatment recommendations have been proposed to treat relapsing horses. These include prolonging the standard treatment course, combining various classes of antiprotozoal agents, using higher doses of triazine antiprotozoal agents, instituting maintenance therapy following the initial treatment course, and administering immunomodulators.

  • Intermittent use of antiprotozoal agents has shown promise in the prevention of EPM. Such protocols have been able to reduce clinical signs, delay seroconversion, and decrease intrathecal anti–S neurona antibody response under experimental conditions. Seroprevalence of anti–S neurona antibodies has been shown to significantly decline in horses continuously exposed to S neurona through the daily extended use of antiprotozoal agents.

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