Sarcocystis falcatula-associated encephalitis in a free-ranging great horned owl (Bubo virginianus).

A great horned owl (Bubo virginianus) was admitted to a rehabilitation clinic with severe neurologic signs that were unresponsive to supportive care. The animal was euthanatized because of a poor prognosis. Marked granulomatous encephalitis with focal brainstem malacia was detected microscopically. The brainstem was the most severely affected brain location and the only place in which schizonts and merozoites, morphologically compatible with Sarcocystis spp., were detected. Immunohistochemistry with the use of polyclonal antisera indicated the presence of Sarcocystis falcatula. The species identification of the protozoa as S. falcatula was confirmed by polymerase chain reaction. To the author's knowledge, this is the first report of spontaneous S. falcatula-associated encephalitis in a great horned owl.