Photomicrographs from a sea otter (Enhydra lutris) found dead in Washington State, USA.

Photomicrographs from a sea otter (Enhydra lutris) found dead in Washington State, USA. (A) Brain – Multiple developing stages of Sarcocystis neurona are present within a glial nodule, including immature schizonts with multi-lobed nuclei (arrowheads); a schizont with developing merozoites (asterisk); and multiple schizonts within two phagocytic cells (arrows). H&E stain. A schizont stains IHC positive for S. neurona (inset). (B) Eye - Multiple protozoal schizonts are present within a focal area of the retina of the left eye (arrows). In this area the inner and outer nuclear layers are focally disorganized and the retina is infiltrated by small numbers of lymphocytes and macrophages. H&E stain. (C) Heart – A thick-walled, mature Sarcocystis sp. cyst (arrow) is present within a myofiber. H&E stain. (D) Skeletal muscle – A Sarcocystis sp. cyst (arrow) is present within a myofiber.  H&E stain.