Natural Cryptosporidium muris infection of the stomach in laboratory mice.

Histopathological findings were described in naturally infected laboratory mice in conjunction with the presence of oocysts in the feces related to cryptosporidiosis of the stomach. Diagnosis of infection was made by the observation of oocysts which were indistinguishable from those of Tyzzer's original description of Cryptosporidium muris seen in feces. In addition to this, endogenous developmental stages of the parasite in histologic preparations of tissues obtained at the time of postmortem examination were observed only in the gastric glands of the stomach. In light microscopy, numerous small, spherical to ovoid, basophilic developmental stages of the parasite, embedded in the epithelial microvilli of the stomach, were observed. Most gastric glands were dilated and filled with numerous free or embedded parasites. The gastric glands contained degenerated and atrophied epithelial cells. However, no signs suggested acute inflammation. No lesions or parasites were found in other portions of the gastrointestinal tract or other epithelial tissues of the body.