Sarcocystis muris--a rare case in laboratory mice.

In a lifespan transgeneration study under standard laboratory conditions using a total of 4682 CBA/J mice, unusual intramuscular inclusions were found in the diaphragm, heart and skeletal muscle of one mouse using light microscopy. Located within the myocytes, they caused no visible tissue reaction. Cross-sections of these spherical and cystic lesions showed numerous banana-shaped structures, identified as permanent parasitic bradyzoites, which permitted these infections to be diagnosed microscopically as sarcocystosis.