Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2004
Publication Date: 5/24/2004
Citation: Saville, W.A., Dubey, J.P., Oglesbee, M.J., Sofaly, C.D., Marsh, A.E., Elitsur, E., Vianna, M.C., Lindsay, D.S., Reed, S.M. 2004. Experimental infection of ponies with sarcocystis fayeri and differentiation from Sarcocystis neurona infections in horses. Journal of Parasitology. 90:1487-1491. Interpretive Summary: Sarcocystis neurona is a single-celled parasite that causes a fatal neurologic disease in horses, equine protozoal myeloencephalitis (EPM). It is difficult to diagnose EPM in live animals. Scientists at the Beltsville Agricultural Research Center and the Ohio State University report that infection with a related parasite, Sarcocystis fayeri, can interfere with diagnosis using an indirect fluorescent antibody test. The results will be of interest to biologists, parasitologists and veterinarians.
Technical Abstract: Sarcocystis neurona and S Sarcocystis neurona arcocystis fayeri infections are common in horses in Americas. Their antemortem diagnosis is important because the former causes a neurological disorder in horses whereas the latter is considered nonpathogenic. There is a concern that equine antibodies to S. fayeri might react with S. neurona antigens in diagnostic tests. In the present study 4 ponies without demonstrable serum antibodies to S. neurona by Western immunoblot were used. Three ponies were fed 105 to 107 sporocysts of S. fayeri obtained from dogs that were fed naturally-infected horse muscles. All ponies remained asymptomatic until the termination of the experiment day 79 post inoculation (PI). All serum samples collected were negative for antibodies to S. neurona using the Western blot at the initial screening, just prior to inoculation with S. fayeri (day 2) and weekly until day 79 PI. Cerebrospinal fluid (CSF) samples from each pony were negative for S. neurona antibodies. Using the S. neurona agglutination test, antibodies to S. neurona were not detected in 1:25 dilution of sera from any samples except pony no. 4 on day 28; this pony had received 107 sporocysts. Seven serum samples using indirect fluorescent antibody tests (IFAT) were positive for S. neurona antibodies from 1:25 to 1:400 dilutions. Sarcocystis fayeri sarcocysts were found in striated muscles of all inoculated ponies with heaviest infections in tongue. All sarcocysts examined histologically appeared to contain only metrocytes. Ultrastructurally, S. fayeri sarcocysts could be differentiated from S. neurona sarcocysts by the microtubules (mt) in villar protrusions on sarcocyst walls; in S. fayeri the mt extended from the villar tips to the pellicle of zoites whereas in S. neurona the mt were restricted to the middle of the cyst wall. Results indicate that horses with S. fayeri infections may be misdiagnosed as S. neurona infections using the IFAT and further research is needed on the serologic diagnosis of S. neurona infections.