Veterinary Parasitology 95 (2001) 167–178 Comparison of Sarcocystis neurona isolates derived from horse neural tissue L.S. Mansfield a,b,c,∗ , H.C. Schott II a , A.J. Murphy c , M.G. Rossano a , S.M. Tanhauser d , J.S. Patterson c , K. Nelson a , S.L. Ewart a , J.V. Marteniuk a , D.D. Bowman e , J.B. Kaneene a,c a Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA b Department of Microbiology and Molecular Genetics, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA c Animal Health Diagnostic Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA d Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA e Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA Abstract Sarcocystis neurona is a protozoan parasite that can cause neurological deficits in infected horses. The route of transmission is by fecal–oral transfer of sporocysts from opossums. However, the species identity and the lifecycle are not completely known. In this study, Sarcocystis merozoites from eight isolates obtained from Michigan horses were compared to S. neurona from a Califor- nia horse (UCD1), Sarcocystis from a grackle (Cornell), and five Sarcocystis isolates from feral opossums from Michigan. Comparisons were made using several techniques. SDS–PAGE analysis with silver staining showed that Sarcocystis spp. from the eight horses appeared the same, but different from the grackle isolate. One Michigan horse isolate (MIH6) had two bands at 72 and 25 kDa that were more prominent than the UCD1 isolate and other Michigan horse isolates. Western blot analysis showed that merozoites of eight of eight equine-derived isolates, and the UCD1 S. neurona isolate had similar bands when developed with serum or CSF of an infected horse. Major bands were seen at 60, 44, 30, and 16 kDa. In the grackle (Cornell) isolate, bands were seen at 60, 44, 29, and 16 kDa. DNA from merozoites of each of the eight equine-derived isolates and the grackle-derived isolate ∗ Corresponding author. Present address: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA. Tel.: +1-517-432-6309; fax: +1-517-432-2310. E-mail address: mansfie4@cvm.msu.edu (L.S. Mansfield). 0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0304-4017(00)00388-5