Exposure to Sarcocystis spp. in horses from Spain determined by Western blot analysis using Sarcocystis neurona merozoites as heterologous antigen

Horses serve as an intermediate host for several species of Sarcocystis, all of which utilize canids as the definitive host. Sarcocystis spp. infection and formation of latent sarcocysts in horses often appears to be subclinical, but morbidity can occur, especially when the parasite burden is large. A serological survey was conducted to determine the presence of antibodies against Sarcocystis spp. in seemingly healthy horses from the Galicia region of Spain. Western blot analyses using Sarcocystis neurona merozoites as heterologous antigen suggested greater than 80% seroprevalance of Sarcocystis spp. in a sample set of 138 horses. The serum samples were further tested with enzyme-linked immunosorbent assays (ELISAs) based on recombinant S. neurona-specific surface antigens (rSnSAGs). As expected for horses from the Eastern Hemisphere, less than 4% of the serum samples were positive when analyzed with either the rSnSAG2 or the rSnSAG4/3 ELISAs. An additional 246 horses were tested using the rSnSAG2 ELISA, which revealed that less than 3% of the 384 samples were seropositive. Collectively, the results of this serologic study suggested that a large proportion of horses from this region of Spain are exposed to Sarcocystis spp. Furthermore, the anti-Sarcocystis seroreactivity in these European horses could be clearly distinguished from anti-S. neurona antibodies using the rSnSAG2 and rSnSAG4/3 ELISAs.