Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 3, 1995
Publication Date: N/A
Interpretive Summary: Sarcocystis neurona is a protozoan (single celled) parasite of horses. Which causes a fatal neurologic disorder. The disease is confined to the Americas. Its life cycle and sources of infection are unknown. Scientists at the Beltsville Agricultural Research Center and the University of Kentucky have identified the American opossum as a possible source of infection based on DNA analysis of the parasite recovered from the intestine of naturally infected opossums. If proven, it will be an important finding in the control of this disease.
Sarcocystis neurona is an apicomplexan which causes equine protozoal myeloencephalis (EPM) in North and South America. Horses appear to be an aberrant host, because the merozoites continually divide in the central nervous system without encysting. The natural host species has not previously been identified. The small subunit ribosomal RNA (SSURNA) gene of S. neurona was compared to those of S. muris, S. cruzi, Toxoplasma gondii and Cryptosporidium parvum to identify a unique region suitable for a species specific amplification primer. The S. neurona SSURNA primer was used in a PCR assay for the purpose of identifying this organism in feces and intestinal digests of wildlife specimens. Sporocysts were isolated for 4 raccoons (Procyon lotor), 2 opossums (Didelphis virginiana) 7 skunks (Mephitis mephitis), 6 cats (Felis catus), 1 hawk (Accipiter sp.) and 1 coyote (Canis latrans). The S. neurona SSURNA PCR assay and a control PCR assay using protist specific primers were applied to all sporocyst DNA samples. All sporocyst DNA samples tested positive on the control assay. The SSURNA PCR assay yielded a 484 bp product only when applied to opossum samples. The SSURNA gene of both opossum sporocyst samples was sequenced to determine its relationship to the S. neurona SSURNA gene. The sequence had 99.89% similarity with S. neurona. This suggests that opossums are the definitive host of S. neurona.