IDENTIFICATION OF OPOSSUMS (DIDELPHIS-VIRGINIANA) AS THE PUTATIVE DEFINITIVE HOST OF SARCOCYSTIS-NEURONA

Sarcocystis neurona is an apicomplexan that causes equine protozoal my eloencephalitis (EPM) in North and South America. Horses appear to be an aberrant host, because the merozoites continually divide in the cen tral nervous system, without encysting. The natural host species has n ot previously been identified. The small subunit ribosomal RNA (SSURNA ) gene of S. neurona was compared to those of Sarcocystis muris, Sarco cystis cruzi, Toxoplasma gondii, and Cryptosporidium parvum to identif y a unique region suitable for a species-specific amplification primer . The S. neurona SSURNA primer was used in a polymerase chain reaction (PCR) assay for the purpose of identifying this organism in feces and intestinal digest of wildlife specimens. Sporocysts were isolated fro m 4 raccoons (Procyon lotor), 2 opossums (Didelphis virginiana), 7 sku nks (Mephitis mephitis), 6 cats (Felis catus), 1 hawk (Accipiter sp.), and 1 coyote (Canis latrans). The S, neurona SSURNA PCR assay and a c ontrol PCR assay using protist-specific primers were applied to all sp orocyst 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.