Cryptosporidiosis (Cryptosporidium spp.)--A CDC Review.

* Causal Agent--Many species of Cryptosporidium can infect humans and a wide range of animals. Although Cryptosporidium parvum and Cryptosporidium hominis (formerly known as C. parvum anthroponotic genotype or genotype 1) are the most prevalent species causing disease in humans, infections by C. felis, C. meleagridis, C. canis, and C. muris also have been reported.

* Life Cycle--Sporulated oocysts, containing four sporozoites, are excreted by the infected host through feces and possibly through other routes, such as respiratory secretions. Transmission of Cryptosporidium parvum and C. hominis occurs mainly through contact with contaminated water (e.g., drinking or recreational water). Occasionally food sources such as chicken salad may serve as vehicles for transmission. Many outbreaks in the United States have occurred in water parks, community swimming pools, and daycare centers. Zoonotic and anthroponotic transmission of C. parvum and anthroponotic transmission of C. hominis occur through exposure to infected animals or exposure to water contaminated by feces of infected animals. Following ingestion (and possibly inhalation) by a suitable host, excystation occurs. The sporozoites are released and parasitize epithelial cells of the gastrointestinal tract or other tissues such as the respiratory tract. In these cells, the parasites undergo asexual multiplication (schizogony or merogony) and then sexual multiplication (gametogony) producing microgamonts (male) and macrogamonts (female). Upon fertilization of the macrogamonts by the microgametes, oocysts develop and sporulate in the infected host. Two types of oocysts are produced: the thick-walled type, which is commonly excreted from the host, and the thin-walled type, which is primarily involved in autoinfection. Oocysts are infective upon excretion, thus permitting direct and immediate fecal-oral transmission. Note that oocysts of Cyclospora cayetanensis, another important coccidian parasite, are unsporulated at the time of excretion and do not become infective until sporulation is completed.

* Geographic Distribution--Since the first reports of human cases in 1976, Cryptosporidium has been found worldwide. Outbreaks of cryptosporidiosis have been reported in several countries, the most remarkable being a waterborne outbreak in Milwaukee, Wisconsin, in 1993 that affected more than 400,000 people.

* Clinical Features--Infection with Cryptosporidium spp. results in a wide range of manifestations, from asymptomatic infections to severe, life-threatening illness. Watery diarrhea is the most frequent symptom and can be accompanied by dehydration, weight loss, abdominal pain, fever, nausea, and vomiting. In immunocompetent people, symptoms are usually short-lived (one to two weeks): they can be chronic and more severe in immunocompromised patients. While the small intestine is the site most commonly affected, symptomatic Cryptosporidium infections also have been found in other organs, including other digestive-tract organs, the lungs, and possibly conjunctiva.

* Laboratory Diagnosis--Acid-fast staining methods, with or without stool concentration, are most frequently used in clinical laboratories. For greatest sensitivity and specificity, immunofluorescence microscopy is the method of choice (followed closely by enzyme immunoassays). Molecular methods are mainly a research tool.

* Treatment--There is no established specific therapy for human cryptosporidiosis. Rapid loss of fluids because of diarrhea can be managed by fluid and electrolyte replacement. Infection in healthy, immunocompetent persons is self-limited. Nitazoxanide has provided some encouraging results in the management of cryptosporidial diarrhea in immunocompetent patients and has been approved by the Food and Drug Administration for treatment of cryptosporidiosis in immunocompetent children under 12 years of age. Immunocompromised people and those in poor health are at highest risk for severe illness. For people with AIDS, anti-retroviral therapy, which improves immune status, also reduces oocyst excretion and decreases diarrhea associated with cryptosporidiosis.

(Adapted from "Parasites and Health: Cryptosporidiosis," CDC Division of Parasitic Diseases. For more information, visit www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/default.htm.)