Cryptosporidium: Its biology and potential for environmental transmission

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Abstract
Protozoans of the genus Cryptosporidium are small (2 to 6 μm, depending on life cycle stage) coccidian parasites that reside within the microvillous region of the mucosal epithelium of man and a variety of animals. Infections with Cryptosporidium spp. were considered rare in animals, and in man they were thought to be the result of a little‐known opportunistic pathogen outside its normal host range. Our concept of Cryptosporidium has changed within the past 4 years to that of a significant and widespread cause of diarrheal illness in several animal species, especially calves and humans. In immunocompetent humans, this protozoan may produce a mild to severe diarrheal illness lasting from several days to more than 1 month. In immune‐deficient persons, especially those with the acquired immune deficiency syndrome (AIDS), cryptosporidiosis usually presents a prolonged, life‐threatening, cholera‐like illness. Treatment of cryptosporidiosis, especially in immune‐deficient persons, has been for the most part unsuccessful. This paper reviews much of our present knowledge of the taxonomy, life cycle, epidemiology, pathology, treatment, and diagnosis of this zoonotic protozoan.