Description of a species of Sarcocystis (Apicomplexa: Sarcocystidae), a parasite of the northern saw-whet owl, Aegolius acadicus, and experimental transmission to deer mice Peromyscus maniculatus

Sporocysts of Sarcocystis were recovered from the intestinal mucosa of a northern saw-whet owl (Aegolius acadicus). Sporocysts measured 12.0 × 9.7 μm (9.6–14.0 × 8.0–12.0 μm; n = 100). Doses of 0, 500, and 2500 sporocysts were administered orally to five deer mice (Peromyscus maniculatus) and five Swiss-Cox white mice (Mus musculus) At necropsy, 28 days postinoculation, deer mice administered 500 and 2500 sporocysts had sarcocysts in skeletal muscles and cardiac muscle. White mice were negative at all dose levels. Sarcocysts had a thin wall (< 1 μm) that consisted of a primary cyst wall and a coarse granular layer composed of 36.6 nm granules (25.6–51.2 nm; n = 11). Thickness of the primary cyst wall was 62.5 nm (38.4–116.1 nm; n = 10). Metrocytes were 2.3 × 1.7 μm (1.5–3.5 × 1.2–2.5 μm; n = 25). Bradyzoites were 5.2 × 1.1 μm (4–7 × 1–2 μm; n = 25).