Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 10, 1999
Publication Date: N/A
Interpretive Summary: Sarcocystis neurona is a protozoan (single-celled) parasite. It causes equine protozoal myeloencephalitis (EPM) in horses. EPM is the most common cause of neurological disorders in horses. Affected horses may develop lameness, paralysis, and some die acutely. Sarcocystis neurona is found in the brain and spinal cord of horses. The opossum (Didelphis virginiana) is sconsidered the reservoir host for S. neurona and the resistant stage of th parasite (oocyst) is shed in opossum feces. However, S. neurona has not been isolated from opossum feces. Scientists at Beltsville Agricultural Research Center, Montana State University and Virginia Tech have distinguished S. neurona from a closely related S. falcatula, also found in opossum feces. In addition, they have discovered a new S. neurona-like species in opossum feces. These results will be of use to biologists, parasitologists and veterinarians.
Sarcocystis neurona was isolated in nude mice and gamma- interferon knockout mice fed sporocysts from faeces of naturally infected opossums (Didelphis virginiana). Mice fed sporocysts became lethargic and developed encephalitis. Protozoa were first found in the brain starting 21 days post innoculation. Sarcocystis neurona was first recovered in cell culture from the homogenate of liver, spleen, and brain of a nude mouse 11 days after feeding sporocysts. The protozoa in mouse brain and in cell culture multiplied by schizogony and mature schizonts often had a residual body. Sarcocystis falcatula, which has an avian- opossum cycle, was not infective to nude or knockout mice. Protozoa were not found in tissues of nude mice or knockout mice after subcutaneous injection with culture-derived S. falcatula merozoites and sporocysts from the faeces of opossums presumed to contain only S. falcatula. Results demonstrate that S. neurona is distinct antigenically and structurally from S. falcatula and opossums are hosts for both species.