Submitted to: Journal of Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2008
Publication Date: 12/30/2008
Citation: Crowdus, C., Marsh, A., Saville, W.J., Lindsay, D.S., Dubey, J.P., Granstrom, D.E., Howe, D.K. 2008. SnSAG5 is an alternative surface antigen of Sarcocystis neurona strains that is mutually exclusive to SnSAG1. Journal of Parasitology. 158:36-43. Interpretive Summary: Sarcocystis species are single celled parasites that cause illness in humans and livestock. Humans can become infected with this parasite by ingesting infected pork and beef. Cattle and pigs can become infected by ingesting food and water contaminated with the resistant parasite stages excreted in feces of infected humans. Many species of Sacrcocystis are pathogenic to animals. Sarcocystis neurona causes fatal encephalitis in many animals, including pets. Scientists at the Beltsville Agricultural Research Center and University of Kentucky report antigenic variation among isolates of S. neurona. The results will be of interest to biologists, parasitologists, and veterinarians.
Technical Abstract: Sarcocystis neurona is an obligate intracellular parasite that causes equine protozoal myeloencephalitis (EPM). Previous work has identified a gene family of paralogous surface antigens in S. neurona called SnSAGs. These surface proteins are immunogenic in their host animals, and are therefore candidate molecules for development of diagnostics and vaccines. However, SnSAG diversity exists in strains of S. neurona, including the absence of the major surface antigen gene SnSAG1. Instead, sequence for an alternative SnSAG has been revealed in two of the SnSAG1-deficient strains. Herein, we present data characterizing this new surface protein, which we have designated SnSAG5. The results indicated that the protein encoded by the SnSAG5 sequence is indeed a surface-associated molecule that has characteristics consistent with the other SAGs identified in S. neurona and related parasites. Importantly, Western blot analyses of a collection of S. neurona strains demonstrated that six of 13 parasite isolates express SnSAG5 as a dominant surface protein instead of SnSAG1. Conversely, SnSAG5 was not detected in SnSAG1-positive strains. One strain, which was isolated from the brain of a sea otter, did not express either SnSAG1 or SnSAG5. Genetic analysis with SnSAG5-specific primers confirmed the presence of the SnSAG5 gene in Western blot-positive strains, while also suggesting the presence of a novel SnSAG sequence in the SnSAG1-deficient, SnSAG5-deficient otter isolate.