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Investigation of the SnSAG gene family of surface antigens in the coccidian parasite Sarcocystis neurona
Department of Veterinary Sciences
Equine protozoal myeloencephalitis (EPM) is a common and debilitating neurolgic disease of horses that is caused by the protozoan pathogen Sarcocystis neurona. Efforts to correctly diagnose, treat, and prevent EPM have been partly hampered by a lack of information about the pathogen. This project will investigate a group of parasite surface proteins that are very immunogenic and likely important for the pathogen's survival. The information gained from these studies could lead to better EPM diagnostics and a protective vaccine.
2010 Project Description
Expression of the Sarcocystis neurona SnSAGs has been examined during the three major life cycle stages (merozoites, bradyzoites, sporozoites). These analyses have demonstrated that the SnSAG surface proteins are differentially regulated in each of the stages. Western blot analyses of S. neurona strain SN138 sporozoites indicated that SnSAG2, SnSAG3, and SnSAG4 are present during this life cycle stage but the SnSAG5 major surface antigen of this strain is not expressed or is significantly down-regulated relative to the other SnSAGs. Immunohistochemical staining of SN138 strain S. neurona bradyzoites implied that all four major SnSAGs expressed by this strain (SnSAG2-SnSAG5) are down-regulated during this latent parasite stage, which is consistent with what has been found for the TgSAGs of the related parasite Toxoplasma gondii.
This research has been conducted by a graduate student at the M.H. Gluck Equine Research Center as part of her dissertation project. Collaboration with investigators at Virginia Tech, Rood and Riddle Equine Hospital and the equine testing company Equine Diagnostic Solutions (EDS), LLC has demonstrated the utility of the modified SnSAG ELISAs as ancillary tests for diagnosis of equine protozoal myeloencephalitis (EPM). Information about the ELISAs and their use for EPM diagnosis was disseminated via multiple abstracts and presentations at the 2010 American College of Veterinary Internal Medicine meeting. The assays have been licensed by EDS and are now offered for commercial testing of serum/CSF samples submitted by veterinary practitioners.
In collaboration with Dr. Udeni Balasuriya at the M.H. Gluck Equine Research Center, recombinant equine arteritis virus cDNAs were designed and constructed to express the SnSAGs. Preliminary analyses of the recombinant viruses suggested that infectious viral particles were produced from the cDNAs and the incorporated SnSAG was faithfully expressed in infected cells. These EAV:SnSAG recombinant viruses will be tested for their ability to elicit immune responses against the parasite proteins.
The SnSAG surface antigens are abundant and highly immunogenic parasite proteins expressed by the equine pathogen Sarcocystis neurona. In-depth characterization of the SnSAGs and the identification of new parasite surface proteins is providing insight into the importance of these molecules during S. neurona infection and intracellular propagation.
As well, this information is being used to enhance our efforts to develop improved diagnostics and protective vaccination against the debilitating neurologic disease EPM. Specifically, the findings of this project have shown that there is variation in the profile of SnSAGs expressed in different strains of S. neurona and during different life cycle stages. These parasite antigenic variations will impact the immune response in infected horses and must be considered when developing and using new diagnostic tests or vaccines.
Furr, M., Howe, D., Reed, S., and Yeargan, M. 2010. Antibody coefficients for the diagnosis of Equine Protozoal Myeloencephalitis. Journal of Veterinary Internal Medicine, doi: 10.1111/j.1939-1676.2010.0658.x.
Yeargan, M.R., and D.K. Howe. 2010. Improved detection of equine antibodies against Sarcocystis neuronausing polyvalent ELISAs based on the parasite SnSAG surface antigens. Veterinary Parasitology, doi: 10.1016/j.vetpar.2010.10.034.