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INTRODUCTION

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Cyclospora cayetanensis is a coccidian parasite that causes acute or chronic, food- and waterborne diarrhea in both immunocompetent and immunocompromised hosts. Cyclospora is a distinct protozoan genus phylogenetically related to other coccidian parasites, including Cryptosporidium, Cystoisospora, Toxoplasma, and Sarcocystis. Initially described in 1979 as cyanobacteria-like (blue-green algae) bodies in the stools of patients in Papua New Guinea with prolonged diarrhea, anorexia, and fatigue, Cyclospora species are now known to be ubiquitous, infecting a variety of animals, birds, reptiles, insectivores, and rodents. However, C cayetanensis is the only species that is known to infect humans, and the role of animals as a natural reservoir is uncertain.

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PATHOGENESIS AND EPIDEMIOLOGY

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Cyclospora are obligate intracellular parasites able to complete all their life cycle within the human host. The species has an anterior polar complex that allows penetration into host cells, but the exact mechanism by which it interacts with human host target cells to cause disease is poorly understood. The oocysts of C cayetanensis are spherical to ovoid, about 8 to 10 μm in size, and surrounded by a thick wall. They are smaller than Cystoisospora belli and twice the size of Cryptosporidium parvum. Infection occurs after the ingestion of sporulated oocysts. During excystation, sporozoites are released and undergo asexual reproduction (merogony and schizogony) and sexual maturation (gametogony) within the host’s gastrointestinal epithelium. The gross appearance of the small intestines of symptomatic patients may reveal moderate to severe erythema. Histopathologically, acute and chronic inflammation is seen with intraepithelial lymphocytic infiltrates. Varying degrees of villous atrophy, crypt hyperplasia, parasitophorous vacuoles, reactive hyperemia, and vascular dilatation are observed. All stages of the C cayetanensis life cycle have been observed in the enterocytes. As opposed to cryptosporidiosis, when Cyclospora oocysts are passed in stools, they are unsporulated and noninfectious, making direct, person-to-person transmission unlikely. Oocysts sporulate in the environment in conditions of high temperature (22–32°C) and humidity in about 1 to 2 weeks producing 2 sporocysts per oocyst. The oocysts can persist in the soil, on food, and in water (where they can survive for 2 months at 4°C and for 7 days at 37°C). The oocysts can be resistant to most disinfectants used in food and water processing (eg, iodine or chlorine). Washing of fruits and vegetables, therefore, may not be sufficient to eliminate the risk of transmission. The high attack rates after foodborne infection suggest a low infective dose of about 10 to 100 organisms, but this has not been precisely quantified.

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Although C cayetanensis has a broad worldwide geographic distribution, infection is most frequently reported from tropical and subtropical countries, especially Latin America (eg, Peru, Guatemala, Mexico), the Indian subcontinent, Southeast Asia, and Caribbean Islands. In these endemic areas, cyclosporiasis prevalence ranges from 2% to 18%, and infection is associated with poor sanitation and contamination of water, food, and soil, with 70% of infections occurring in people younger than 20 years of ...

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