Equine Protozoal Myeloencephalitis Associated with Neosporosis in 3 Horses

A 24-year-old Appaloosa gelding was evaluated for a 2-month history of pelvic limb incoordination. The gelding had been administered phenylbutazone (2 mg/kg PO q12h) for 1 week before admission, and no improvement was apparent. Two months before presentation, the gelding had been vaccinated against Eastern and Western equine encephalitis (EEE, WEE), tetanus, influenza, West Nile virus (WNV), and rabies. Deworming was adequate, with oral dewormers rotated between ivermectin and pyrantel pamoate every 2 months. On admission, the gelding was tachycardic (52 beats per minute), normothermic (37uC, 99.0uF), and eupneic (16 breaths per minute). Muscling appeared symmetric; however, the gelding placed more weight on the right pelvic limb than on the left and the tail was held to the right side. A complete neurologic evaluation revealed asymmetric hypermetria, characterized by a grade 2 of 5 ataxia on the left thoracic and left pelvic limbs and a grade 3 of 5 ataxia on the right thoracic and right pelvic limbs. There were no cranial nerve deficits, and both tail tone and were normal. The gelding was observed to urinate and defecate normally. A CBC revealed a leukocytosis (14,000/mL; reference range, 5,000–11,600/mL) characterized by a mature neutrophilia (12,200/mL; reference range, 2,600–6,800/ mL). Serum biochemical abnormalities included hyper-glycemia (124 mg/dL; reference range, 50–107 mg/dL). Findings of cervical radiographs revealed mild osteoar-throsis of the articular facets at C4-5 and C5-6. Lumbosacral cerebrospinal collection was performed, and clear cerebrospinal fluid (CSF) fluid was obtained and submitted for cytology, serology (immunoglobulin M [IgM] capture ELISA) for WNV, and indirect fluorescent antibody testing (IFAT) for equine pro-tozoal myeloencephalitis (EPM) (Sarcocystis neurona and Neospora hughesi). The CSF total nucleated cell count (TNCC) was normal (1/mL; reference range, ,6/ mL) with the cell population consisting primarily of small mononuclear cells (70%), large mononuclear cells (17%), and neutrophils (13%). The CSF protein concentration was normal (47 mg/dL; reference range, 20– 70 mg/dL). Red blood cell (RBC) concentration within the CSF was 8/mL. The IgM capture ELISA was negative for WNV. S neurona IFAT titers were negative in serum (,40) and CSF (,5), whereas the serum and CSF tested positive for N hughesi, with titers of 2,560 and 5, respectively. A diagnosis of EPM associated with N hughesi was made, and the gelding was started on a course of ponazuril (5 mg/kg PO q24h for 30 days) and phenylbutazone (2 mg/kg PO sid for 14 days). A repeat examination was performed after …