title: Are Sarcocystis neurona and Sarcocystis falcatula synonymous? A horse infection challenge.
abstract: Equine protozoal myeloencephalitis (EPM) is a debilitating neurologic disease of the horse. The causative agent. Sarcocystis neurona, has been suggested to be synonymous with Sarcocystis falcatula, implying a role for birds as intermediate hosts. To test this hypothesis, opossums (Didelphis virginiana) were fed muscles containing S. falcatula sarcocysts from naturally infected brown-headed cowbirds (Molothrus ater). Ten horses were tested extensively to ensure no previous exposure to S. neurona and were quarantined for 14 days, and then 5 of the horses were each administered 10(6) S. falcatula sporocysts collected from laboratory opossums. Over a 12-wk period, 4 challenged horses remained clinically normal and all tests for S. neurona antibody and DNA in serum and cerebrospinal fluid were negative. Rechallenge of the 4 seronegative horses had identical results. Although 1 horse developed EPM, presence of S. neurona antibody prior to challenge strongly indicated that infection occurred before sporocyst administration. Viability of sporocysts was confirmed by observing excystation in equine bile in vitro and by successful infection of naive brown-headed cowbirds. These data suggest that S. falcatula and S. neurona are not synonymous. One defining distinction is the apparent inability of S. falcatula to infect horses, in contrast to S. neurona, which was named when cultured from equine spinal cord.
authors.affiliation: Department of Pathobiology, College of Veterinary Medicine, University of Florida, Gainesville 32611-0880, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Cutler
authors.forename: R J
authors.initials: RJ
authors.lastname: MacKay
authors.forename: P E
authors.initials: PE
authors.lastname: Ginn
authors.forename: E C
authors.initials: EC
authors.lastname: Greiner
authors.forename: R
authors.initials: R
authors.lastname: Porter
authors.forename: C A
authors.initials: CA
authors.lastname: Yowell
authors.forename: J B
authors.initials: JB
authors.lastname: Dame
mesh_terms: D000818:Animals; D001715:Bird Diseases / Q000469:parasitology; D001717:Birds; D004660:Encephalitis / Q000469:parasitology / Q000473:pathology / Q000662:veterinary; D006734:Horse Diseases / Q000469:parasitology* / Q000473:pathology; D006736:Horses / Q000469:parasitology; D006790:Host-Parasite Interactions; D009893:Opossums / Q000469:parasitology*; D012522:Sarcocystis / Q000145:classification* / Q000254:growth & development / Q000472:pathogenicity*; D012523:Sarcocystosis / Q000469:parasitology / Q000473:pathology / Q000662:veterinary*