Natural fatal Sarcocystis falcatula infections in free-ranging eagles in North America.

Three bald eagles (Haliaeetus leucocephalus) and 1 golden eagle (Aquila chrysaetos) were admitted to rehabilitation facilities with emaciation, lethargy, and an inability to fly. Intravascular schizonts and merozoites were present in 2 bald eagles, mainly in the lung tissue, whereas the third bald eagle and the golden eagle had lymphohistiocytic encephalitis with intralesional schizonts and merozoites. In all eagles, protozoal tissue cysts were present in skeletal musculature or heart. The protozoal organisms were morphologically compatible with a Sarcocystis sp. By immunohistochemistry, the protozoal merozoites were positive for Sarcocystis falcatula antigen in all cases when using polyclonal antisera. Furthermore, the protozoa were confirmed to be most similar to S. falcatula by polymerase chain reaction in 3 of the 4 cases. To the authors' knowledge, this report presents the first cases of natural infection in eagles with S. falcatula as a cause of mortality.