Detection of Sarcocystis neurona infection in horses

Equine protozoal myeloencephalitis (EPM) is a well-recognized neurological disease in North and South America caused primarily by Sarcocystis neurona. Detection of antibodies to the parasites associated with disease by western blot is the current method to assess possible infection. A major disadvantage of currently available tests is whole parasite preparations are used as antigen which is time consuming and labor intensive. Moreover, whole parasite antigen preparations may contain epitopes conserved among other members in the genera Sarcocystis and potential other apicomplexan parasites which could result in cross-reactivity with antibodies directed to these parasites. The sera from exposed animals react strongly to ∼29 kilodalton S. neurona surface Antigen 1 (SnSAG1) by immunoblot analysis suggesting that this is an immunodominant surface antigen. The SnSAG1 gene was expressed as recombinant antigen in insect cells using the baculovirus system. The present study indicates that recombinant SnSAG1-Bac antigen, expressed in baculovirus system, can be a potential diagnostic antigen for detection of S. neurona antibodies because it was recognized by antibodies in sera/CSF of S. neurona naturally infected and experimentally immunized horses and non-equid species. In addition, it proved to be S. neurona-specific because anti-sera against related parasites of Sarcocystidae family such as Neospora caninum, Neospora hughesi, a Hammondia sp. and T. gondii did not show any cross-reactivity to the recombinant SnSAG1-Bac antigen.