Initial experiences with the use of nitazoxanide in the treatment of equine protozoal encephalitis in northern California

Equine protozoal myeloencephalitis (EPM) is the most common neurological co ndition affecting houses In North and South America. Nitazoxanide* has been reported tp be effective against a wide variety of parasites and bacteria in both animals and humans, including protozoa, nematades, cestodes, tremat odes, almost all anaerobic obligate and facultative bacteria, and some aero bic bacteria, The purpose of this study was to determine the effectiveness of nitazoxanide for the treatment of EPM in horses, For inclusion in the st udy, horses had to have evidence of proprioceptive deficits in one or more limbs, and have a positive immunoblot (Western blot) assay for Sarcocystis neurona antibodies in cerebrospinal fluid. The degree of ataxia was graded from 0 (none) to 5 (severe). Seven horses fit the criteria for inclusion, f ive horse were grade 2, one horse was a grade 3, and one horse was a grade 4. Nitazoxanide was administered as a feed additive, as tablets, as a powde r, or as a paste at 50 tablets, as a powder, or as a paste at 50 or 75 mg/k g for approximately 28 days. Two horses became inappetent and depressed dur ing the course of treatment. However, no long-term sequelae were noted. Fou r horses became pregnant while on the medication, and remained pregnant at the end of the study period. Neurologic signs returned in two horses, and m edication was re-introduced. By the end of the trial (85 to 140 days), five horses were neurologically normal, one horse had improved from a grade 4 t o a grade 1, and one horse was unchanged. Cerebrospinal fluid samples were obtained from approximately 85 to 140 days after the start of medication. T he samples remained positive for Sarcocystis neurona antibodies by immunobl ot (Western blot). However, in six of the seven horses, the relative quanti ty of antibody had decreased, in its final formulation as a paste, nitazoxa nide was well accepted and well tolerated by horses. It improved the neurol ogical status of six of the seven horses. Nitazoxanide has the advantage ov er presently available medications in that it is cidal (in other species) r ather than static in action, it has been administered to pregnant rodents w ithout inducing signs of fetal abnormalities, and is available in a formula tion that is more easily administered to horses.