Causative Agent

Cyclospora cayetanensis is also a coccidian member of the Apicom-plexa, and its oocysts are similar to those of Cryptosporidium

Table 24.14 Cryptosporidiosis

Symptoms

Fever, loss of appetite, nausea, crampy abdominal pain, watery diarrhea, usually lasting 10 to 14 days.

Incubation period

Usually about 6 days (range, 4 to 12 days)

Causative agent

Cryptosporidium parvum, a coccidian member of the Apicomplexa. Its life cycle takes place entirely within the epithelial cells of the small intestine

Pathogenesis

Following ingestion of oocysts, the intestinal juices cause the release of four banana-shaped sporozoites. The sporozoites invade the epithelial cells, causing deformity of the cells and the intestinal villi and inciting an inflammatory response. Secretion of water and electrolytes increases, and absorption of nutrients decreases.The process is brought under control largely by cell-mediated immunity

Epidemiology

Oocysts of C. parvum are infectious when discharged with the feces.The infectious dose is small, and person-to-person spread readily occurs under unsanitary conditions. Infected individuals can discharge the oocysts for weeks after symptoms subside.The oocysts resist chlorination, and they pass through most municipal water filtration systems.The host range is wide, including cattle, pigs, and dogs.

Prevention and treatment

Pasteurization of beverages such as milk and apple juice, boiling of drinking water, or filtering it using a 1-mm or smaller pore size filter. Sanitary disposal of human and animal feces. No effective treatment exists

24.7 Protozoan Diseases of the Lower Alimentary System 627

parvum, except C. cayetanensis oocysts are larger, about 8 to 10 mm in diameter, and when passed in feces do not yet contain sporozoites. After days under favorable conditions outside the body, two sporocysts each containing two sporozoites develop within each oocyst, which is then infectious. Structural features place the protozoan with the Cyclospora, a genus described in 1881. Studies of its ribosomal RNA base sequence show that it is closely related to members of the genus Eimeria. This is an example of the turmoil arising from molecular biological findings as the newer science challenges the old on the naming of microorganisms.

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