Cysts of a Sarcocystis species were found in large numbers
in skeletal muscle of an otter (Lutra lutra) which was raised
in Norway and died in captivity in Sweden. This is the first report of
Sarcocystis infection in the otter. The sarcocysts
were 0·3–2·3 mm long and 0·06–0·25
mm wide. As judged by light microscopy the sarcocyst walls were thin (<3
μm) with
a serrated surface but without visible projections. By transmission electron
microscopy, the sarcocyst wall measured
0·6–1·8 μm and had minute undulations covering the
entire sarcocyst surface giving the wall a wavy appearance. Septa
were indistinct. The sarcocysts contained few metrocytes and numerous bradyzoites.
Sarcocysts were not found in 69
other otters subjected to necropsy in Sweden.