Cryptosporidiosis Infections

Immunocompetent and Immunodeficient Persons

The disease, cryptosporidiosis, is caused by the coccidian protozoan, Cryptosporidium. The genus contains over 20 species and infects at least 40 different hosts. In humans, C. parvum infection is primarily characterized by profuse, watery diarrhea. The duration of symptoms and outcome of the disease, however, vary according to the immunologic status of the host. Among persons with acquired immunodeficiency syndrome (AIDS), cryptosporidiosis can cause significant morbidity.

Most sources name E. E. Tyzzer as the first to describe Cryptosporidium: In 1907, Tyzzer observed the microorganism in rodent gastric glands. However, in 1895, Clarke also noted a coccidian in the stomach of mice. The genus, Cryptosporidium (which means "hidden spore"), was originally considered a benign commensual (Mannheimer & Soave, 1994, p. 483). Between 1907 and 1955, the microorganism was described in a variety of animal species including turkeys, rattlesnakes, and fox. However, because Cryptosporidium was considered nonpathogenic, it received little attention. It wasn't until the mid-twentieth century that an association was made between Cryptosporidium and diarrhea. Initially, the disease was described in cows, horses, and pigs. Then, in 1976, the first human case of cryptosporidiosis was reported (Sun, 1994, pp. 16-17). A 3-year-old child in rural Tennessee presented with "severe gastroenteritis of 2

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e a somewhat higher prevalence than immunocompetent adults. Cryptosporidium is also a common cause of diarrhea in AIDS patients. It infects approximately 14 percent to 33 percent of all patients with AIDS and diarrhea. In the U.S., the estimated prevalence among AIDS patients is 10 percent to 15 percent (Ritchie & Becker, 1994, pp. 767-775). However, 13 percent to 22 percent of AIDS patients in Africa, and as many as 41 percent of AIDS patients in Haiti harbor Cryptosporidium (Sun, 1994, pp. 16-17). Obviously, cryptosporidiosis occurs in both immunocompetent and immunodeficient persons. Although these two groups have certain features in common, they typically follow two distinct clinical courses. In general, the symptoms of Cryptosporidium infection are highly variable. For example, there are isolated reports of asymptomatic disease. In addition, symptoms may range from self-limited diarrhea to fatal enteritis. The incubation period for humans is roughly 5 to 21 days. Most patients experience profuse, "almost cholera-like watery diarrhea" (Wittner, Tanowitz, & Weiss, 1993, pp. 569-571). This diarrhea may range from a few loose bowel movements to more than 70 stools (greater than 20 liters) per day. In addition to d

Category: Medical - C