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

This study investigates the effects of periodic oral ponazuril administration on equine responses to Sarcocystis neurona, a parasite causing neurological diseases in horses. The findings suggest that weekly administration of ponazuril significantly reduces horse immune responses to S. neurona, with potential implications for preventing Equine Protozoal Myeloencephalitis (EPM).

Research design and methods

• The study involved 20 healthy horses that had not been previously exposed to S. neurona – as evidenced by the absence of S. neurona-specific IgG.
• Testing groups were divided as follows: five untreated control horses that were not inoculated with the parasite, and three groups that were each exposed to 612,500 S. neurona sporocysts via a nasogastric tube on the study’s first day.
• Among the exposed groups, one group did not receive any treatment, while the two others were administered 20 mg/kg of ponazuril orally either every seven days (starting from the fifth day) or every 14 days (starting on the twelfth day) for the duration of 12 weeks.
• The researchers took blood and cerebrospinal fluid (CSF) samples from every horse the day before the study and then every 14 days after the inoculation, which they analyzed via western blot to assess for immune response (immunoconversion).
• They also monitored the horses for symptoms of EPM and examined horse tissues histologically after euthanization.

Research findings

• All horses that were exposed to the parasite showed a positive immune response (as detected by western blot) within 56 days.
• Only two of the five horses treated weekly with ponazuril showed signs of immunoconversion in their CSF, with the rest of the inoculated horses showing signs within 84 days.
• Weekly ponazuril treatment significantly lowered the CSF’s antibody response against a marker of the S. neurona parasite (the 17-kd antigen).
• None of the groups of horses developed EPM symptoms. Likewise, histological examination of their central nervous system tissues did not reveal any signs of the parasite or consistent degenerative or inflammatory changes.

Conclusions and implications of the research

• The administration of ponazuril every seven days (but not every 14 days) significantly reduced the anti-S. neurona antibody response in the horses that were exposed to S. neurona.
• This implies that protocols involving the regular administration of ponazuril could potentially be used to prevent EPM, by modulating the immune response of horses to S. neurona.