The ability of
ponazuril to prevent or limit clinical signs of equine protozoal
myeloencephalitis (EPM) after
infection with Sarcocystis neurona was evaluated. Eighteen horses were assigned to 1 of 3 groups: no treatment, 2.5 mg/kg
ponazuril, or 5.0 mg/kg
ponazuril. Horses were administered
ponazuril, once per day, beginning 7 days before
infection (study day 0) and continuing for 28 days postinfection. On day 0, horses were stressed by transport and challenged with 1 million S. neurona sporocysts per horse. Sequential neurologic examinations were performed, and serum and cerebrospinal fluid were collected and assayed for
antibodies to S. neurona. All horses in the control group developed
neurologic signs, whereas only 71 and 40% of horses in the 2.5 and 5.0 mg/kg
ponazuril groups, respectively, developed neurologic abnormalities. This was significant at P = 0.034 by using Fisher exact test. In addition, seroconversion was decreased in the 5.0 mg/kg group compared with the control horses (100 vs. 40%; P = 0.028). Horses with
neurologic signs were killed, and a post-mortem examination was performed. Mild-to-moderate, multifocal signs of
neuroinflammation were observed. These results confirm that treatment with
ponazuril at 5.0 mg/kg minimizes, but does not eliminate,
infection and clinical signs of EPM in horses.