Effect of intermittent oral administration of ponazuril on experimental Sarcocystis neurona infection of horses

Am J Vet Res. 2008 Mar;69(3):396-402. doi: 10.2460/ajvr.69.3.396.


Objective: To evaluate the effect of intermittent oral administration of ponazuril on immunoconversion against Sarcocystis neurona in horses inoculated intragastrically with S neurona sporocysts.

Animals: 20 healthy horses that were seronegative for S neurona-specific IgG.

Procedures: 5 control horses were neither inoculated with sporocysts nor treated. Other horses (5 horses/group) each received 612,500 S neurona sporocysts via nasogastric tube (day 0) and were not treated or were administered ponazuril (20 mg/kg, PO) every 7 days (beginning on day 5) or every 14 days (beginning on day 12) for 12 weeks. Blood and CSF samples were collected on day - 1 and then every 14 days after challenge for western blot assessment of immunoconversion. Clinical signs of equine protozoal myeloencephalitis (EPM) were monitored, and tissues were examined histologically after euthanasia.

Results: Sera from all challenged horses yielded positive western blot results within 56 days. Immunoconversion in CSF was detected in only 2 of 5 horses that were treated weekly; all other challenged horses immunoconverted within 84 days. Weekly administration of ponazuril significantly reduced the antibody response against the S neurona 17-kd antigen in CSF. Neurologic signs consistent with EPM did not develop in any group; likewise, histologic examination of CNS tissue did not reveal protozoa or consistent degenerative or inflammatory changes.

Conclusions and clinical relevance: Administration of ponazuril every 7 days, but not every 14 days, significantly decreased intrathecal anti-S neurona antibody responses in horses inoculated with S neurona sporocysts. Protocols involving intermittent administration of ponazuril may have application in prevention of EPM.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Administration, Oral
  • Animals
  • Antibodies, Protozoan / blood
  • Antibodies, Protozoan / cerebrospinal fluid
  • Blotting, Western / veterinary
  • Brain / parasitology
  • Coccidiostats / administration & dosage*
  • Encephalomyelitis / immunology
  • Encephalomyelitis / parasitology
  • Encephalomyelitis / prevention & control
  • Encephalomyelitis / veterinary*
  • Female
  • Histocytochemistry / veterinary
  • Horse Diseases / cerebrospinal fluid
  • Horse Diseases / immunology
  • Horse Diseases / parasitology*
  • Horse Diseases / prevention & control*
  • Horses
  • Male
  • Sarcocystis / immunology*
  • Sarcocystosis / immunology
  • Sarcocystosis / parasitology
  • Sarcocystosis / prevention & control
  • Sarcocystosis / veterinary*
  • Triazines / administration & dosage*


  • Antibodies, Protozoan
  • Coccidiostats
  • Triazines
  • ponazuril