Excerpt from Cyclosporiasis

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Background

Cyclospora cayetanensis is a coccidian parasite that infects the GI tract of both immunocompetent and immunocompromised hosts. This organism was first described in human feces in 1979. Since the advent of the acquired immunodeficiency syndrome (AIDS) epidemic, C cayetanensis has been increasingly recognized as an enteric pathogen.¹

Cyclospora species are ubiquitous and infect various animals, including vipers, moles, rodents, and myriapods. Humans are the only known hosts of C cayetanensis. The first known outbreak of cyclosporiasis in the United States occurred in 1990 in a Chicago hospital's physicians' dormitory and was attributed to an infected water source. In 1996-97, US epidemics of cyclosporiasis were attributed to infected Guatemalan raspberries,^{2, 3} basil, and mesclun lettuce.^{4, 5, 6, 7} An outbreak resulted from exposure to contaminated berries at a social function in Ontario, Canada in 1999. More recent outbreaks have been associated with imported Thai basil⁸ and snow peas in a cluster of infections in Pennsylvania in 2004.^{9, 10} Otherwise, only sporadic cases, primarily involving travelers, have been documented.

Pathophysiology

Cyclospora species are variably acid-fast, round-to-ovoid organisms that measure 8-10 µm in diameter. Cyclospora species exogenously sporulate and have 2 sporocysts per oocyst. Transmission follows ingestion of oocysts in fecally contaminated water or produce. Direct person-to-person transmission is considered unlikely because the oocysts are not infectious when excreted; the oocysts undergo sporulation outside the human host before becoming infective. The median incubation period is 1 week, during which time the organism invades enterocytes of the small intestine.

Disease manifests as protracted and relapsing gastroenteritis. Cyclospora species are characterized by an anterior polar complex that allows penetration into host cells, but the life cycle of the parasite and the mechanisms by which it interacts with human host target cells to cause disease are poorly understood.

Frequency

United States

The frequency of cyclosporiasis is unknown.

International

Most fecal isolates have been obtained from residents of developing countries or from travelers returning from these regions. Cyclosporiasis is endemic in Haiti, Nepal, and Peru, with a strong seasonal predominance during rainy spring and summer months. Cyclosporiasis has also been reported in travelers returning from Mexico, Southeast Asia, Puerto Rico, Indonesia,¹¹ Morocco, Pakistan, and India.

Mortality/Morbidity

Death is exceptionally rare. Very little morbidity results from this infection, except in persons with underlying immunosuppression, in whom chronic diarrhea can develop.

Race

No racial predilection has been reported.

Sex

Cyclosporiasis equally affects both sexes.

Age

Persons of all ages can be affected, although cyclosporiasis primarily affects children in developing countries where the disease is endemic.

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