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United States Department of Agriculture

Agricultural Research Service


item Furr, M
item Mckenzie, H
item Saville, W
item Dubey, Jitender
item Reed, S
item Davis, W

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2005
Publication Date: 1/7/2006
Citation: Furr, M., Mckenzie, H., Saville, W.J., Dubey, J.P., Reed, S.M., Davis, W. 2006. Prophylactic administration of ponazuril reduces clinical signs and delays seroconversion in horses challenged with sarcocystis neurona. Journal of Parasitology 92:637-643.

Interpretive Summary: Sarcocystis neurona is a single-celled parasite. It causes a fatal disease in horses called Equine Protozoal Myeloencephalitis (EPM). EPM also occurs in other animals. Opossums are the definitive host for this parasite, and the main reservoir of infection. Opossums become infected by consuming the encysted stage of the parasite (sarcocyst) in infected animal tissue and they excrete millions of the resistant stage (oocysts) in their feces. Horses become infected by ingesting food and water contaminated with oocysts. Scientists at the Beltsville Agricultural Research Center Equine Medical Center , Leesburg, Virginia have found that prophylactic treatment with ponazuril can reduce clinical signs due to EPM. The results will be of interest to biologists, parasitologists, and veterinarians.

Technical Abstract: The ability of ponazuril to prevent or limit clinical signs of equine protozoal myeloencephalitis (EPM) following 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 prior to infection (study day 0) and continuing for 28 days post infection. 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 while only 71 and 40% of horses in the 5.0 and 2.5 mg/kg ponazuril group,respectively developed neurologic abnormalities. This was significant at P=0.034 using Fischers exact test. In addition, seroconversion was decreased in the 5.0 mg/kg group when compared to the control horses (100% versus 40%; P=0.028). Horses with neurologic signs were killed and a post-mortem examination 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.

Last Modified: 09/19/2017
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