Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2000
Publication Date: N/A
Interpretive Summary: Sarcocystis neurona is single-celled parasite that causes a fatal illness in horses called equine protozoal myeloencephalitis (EPM). EPM is the most commonly diagnosed cause of neurologic disorders in horses in the U.S. Horses become infected with S. neurona when they ingest food or water contaminated with sporocyst (resistant stage of S. neurona) excreted in the efeces of the opossum. The prevalence of S. neurona in opossums is unknown A scientist at the Beltsville Agricultural Research Center has found S. neurona in 8 of 47 (18.1%) of road killed opossums. This is the first survey of this parasite in opossums. The findings will be of interest to horse owners, veterinarians and Parasitologists.
Sarcocystis sporocysts were found in intestinal scrapings from 24 (54.5 96) of 44 opossums (Didelphis virginiana). The number of sporocysts varied from a few <10,000) to 245 million. Sporocysts from 23 of 24 opossums were fed to captive budgerigars (Melopsittacus undulatas) and the inocula from 21 opossums were infective, indicating the presence of S. falcatula. Sporocysts from 24 opossums were fed to gamma-interferon-knockout (KO) or nude mice; inocula from 14 opossums were infective to mice. Sarcocystis neurona was detected in tissues of KO mice by specific staining with anti-S. neurona antibodies and parasite was cultured in vitro from the brains of KO mice fed sporocysts from 8 opossums Sarcocystis speeri was identified by specific staining with anti-S. speeri antibodies in tissues of KO mice fed inocula from 8 opossums; 3 opossums h&d mixed S. neurona and S. speeri infections Thus, the prevalences of sporocysts of different species of Sarcocystis in opossums were: S. falcatula 21 of 44 (47.7%), S. neurona 8 of 47 (18.1%) and S. speeri 8 of 44 (18.1%) opossums. Sarcocystis neurona alone was found in 1 opossum, and S. speeri alone was found in 1 opossum. Mixed Sarcocystis infections were present in 21 opossums. The North American opossum (Didelphis virginiana) is the definitive host for at least pathogenic species of Sarcocystis, S. neurona, S. falcatula and S. speeri (Box et al., 1984; Dubey et al., 1991; Fenger et al., 1997; Dubey and Lindsay, 1998, 1999; Dubey et al., 1998). The objective of the present investigation was to determine the prevalence of Sarcocystis species in opossums because there is little information on this subject.