Cyclospora cayetanensis, a unicellular coccidian parasite that causes protracted, relapsing gastroenteritis in humans, was recognized only relatively recently (coccidians are unicellular parasites in the protist phylum Apicomplexa and are known largely as parasites in the intestines of various vertebrates, e.g., Cryptosporidium and Isospora in humans). Looking back, investigators now believe that the first three documented human cases of Cyclospora infection were diagnosed in 1977 and 1978 in Papua New Guinea, but little was published about Cyclospora until the 1990s. Until the 1990s, the genus Cyclospora was only known to include species that infect non-primates (e.g., rodents, moles, and snakes). (Ortega et al. 1994; Herwaldt 2000) Subsequently, parasites identified as Cyclospora were found to infect several primate species. Cyclospora cayetanensis is only known to infect humans. Molecular phylogenetic studies have suggested that C. cayetanensis (and possibly other "Cyclospora" infecting primates) may actually fall within the genus Eimeria rather than Cyclospora (and conceivably has already been previously described as a species of Eimeria) (Pieniazek and Herwaldt 1997; Morrison et al. 2004 and references therein). The role of other animals as reservoirs or intermediate hosts of Cyclospora cayetanensis has been examined with conflicting results. (Ortega and Sanchez 2010 and references therein).
In industrialized regions, cyclosporiasis has been most often linked with either food-borne outbreaks or foreign travel. It appears that in industrialized nations, most people are susceptible to infections, whereas in areas of endemicity, infections are limited mainly to the very old and the very young. Epidemiological studies have shown that increased risk of Cyclospora infection is associated with consumption of untreated water or food, lack of adequate sanitation, contact with soil, and the presence of animals in the household. Outbreaks of cyclosporiasis in the United States have been associated with produce, particularly raspberries, imported from areas where Cyclospora is endemic. Cyclospora infection is often identified in travelers from areas of endemicity (e.g., parts of Haiti, Guatemala, Peru, and Nepal). (Chacín-Bonilla 2008; Ortega and Sanchez 2010)
Although this parasite is believed to require days to weeks outside the host to become infectious, it has repeatedly caused foodborne outbreaks, including large multi-state outbreaks in the United States and Canada. (Herwaldt 2000)
Some of the earliest diagnosed cases of Cyclospora infection in humans were opportunistic infections in AIDS patients in the 1980s (symptoms of infection can be quite severe in this population). Ortega and Sanchez (2010) provide a broad review of Cyclospora infection in humans, including a description of morphology and life cycle, histopathology, epidemiology, diagnosis and treatment, and detection and control in the environment. (Ortega and Sanchez 2010 and references therein)
Cyclosporiasis has been reported from many countries, but is most common in tropical and subtropical areas. Since 1990, at least 11 outbreaks of cyclosporiasis, affecting around 3600 people, have been documented in the United States and Canada. (Source: Centers for Disease Control Parasites and Health Website)