Cyclospora cayetanensis and Cyclosporiasis: An Update

Abstract

Cyclospora cayetanensis is a coccidian parasite of humans, with a direct fecal-oral transmission cycle. It is globally distributed and an important cause of foodborne outbreaks of enteric disease in many developed countries, mostly associated with the consumption of contaminated fresh produce. Because oocysts are excreted unsporulated and need to sporulate in the environment, direct person-to-person transmission is unlikely. Infection by C. cayetanensis is remarkably seasonal worldwide, although it varies by geographical regions. Most susceptible populations are children, foreigners, and immunocompromised patients in endemic countries, while in industrialized countries, C. cayetanensis affects people of any age. The risk of infection in developed countries is associated with travel to endemic areas and the domestic consumption of contaminated food, mainly fresh produce imported from endemic regions. Water and soil contaminated with fecal matter may act as a vehicle of transmission for C. cayetanensis infection. The disease is self-limiting in most immunocompetent patients, but it may present as a severe, protracted or chronic diarrhea in some cases, and may colonize extra-intestinal organs in immunocompromised patients. Trimetoprim-sulfamethoxazole is the antibiotic of choice for the treatment of cyclosporiasis, but relapses may occur. Further research is needed to understand many unknown epidemiological aspects of this parasitic disease. Here, we summarize the biology, epidemiology, outbreaks, clinical symptoms, diagnosis, treatment, control and prevention of C. cayetanensis; additionally, we outline future research needs for this parasite.

Keywords: Cyclospora; control; diagnosis; epidemiology; humans; life cycle.

Figure 1

Life cycle of Cyclospora cayetanensis. Caption: If a susceptible human ingests sporulated oocysts in contaminated food or water, the sporozoites inside the sporocysts excyst in the gut lumen and invade enterocytes of the epithelium of duodenum and jejunum where the sporozoites transform into trophozoites. Trophozoites subsequently form 2 types of schizonts (asexual multiplication). Type I schizonts contain 8–12 merozoites. Type II schizonts contain 4 merozoites. Then, type II merozoites form gamonts (sexual multiplication). There are two types of gamonts: microgamonts and macrogamonts. Microgamonts fertilize macrogamonts to form the zygote. Oocysts then are formed in enterocytes and are excreted unsporulated in the feces. The prepatent period is thought to be around one week. Unsporulated oocysts are not infectious—they need to sporulate to became infective for a host. Under laboratory conditions, at 22 °C and 30 °C, sporulation will take between 7 and 14 days to occur outside the host. A sporulated oocyst contains two sporocysts, each with two sporozoites.

Figure 2

Oocysts of Cyclospora cayetanensis. Caption: Cyclospora cayetanensis oocysts. (A,B), unstained, differential Interference contrast, (C) acid-fast stain, (D) hot-safranin stain, (E), ultraviolet fluorescence microscopy. Oocyst in B is sporulated. Bars in A-E = 5 µm. Images (C–E) were from public images from DPDx CDC.