Cystoisospora (Isospora) and Cyclospora Species

Pathogens

Both C. belli and Cyclospora cayetanensis are intestinal coccidia of the phylum Apicomplexa. Noninfectious, unsporulated oocysts are passed in stools. Sporulation outside the host usually occurs within 7–15 days under ideal conditions (23°C−27°C). When sporulation occurs, oocysts presumably become infectious to a susceptible host. C. belli can be distinguished from Cyclospora spp. by their size and the number of sporozoites in each sporocyst; C. belli have four sporozoites per sporocyst, compared with two sporozoites per sporocyst in Cyclospora spp. ^,

Epidemiology

C. belli infection is endemic in tropical and subtropical climates, especially in developing countries in South America, Africa, and South Asia. ^, The organism has been reported as an etiologic agent of traveler’s diarrhea in visitors to endemic areas and has been implicated in outbreaks in facilities for handicapped people. ^, Cystoisosporiasis has been documented in 15% of patients with acquired immunodeficiency syndrome (AIDS) in Haiti but in <0.2% of patients with AIDS in the US. The presence of the organism almost always is associated with symptoms, and in the US, reports of C. belli usually involve persons with AIDS. Infection in other immunocompromised populations, such as patients with cancer or patients receiving immunosuppressive medications, also has been reported.

C. cayetanensis infections have been documented in both immunocompetent and immunocompromised hosts worldwide. Epidemiologic studies in Peru and Nepal have demonstrated seasonal variation in the number of infections. In Peru, infections peaked between April and June. In Nepal, no infections were diagnosed in the cooler, dry months between December and April. Asymptomatic carriage of the organism has been noted in Peruvian natives. However, in studies of tourists and foreign residents in Nepal, identification of the organism was always associated with diarrhea.

Infection with C. belli and Cyclospora follows ingestion of mature oocysts. Because sporulation occurs outside of the host, direct person-to-person transmission does not occur. Both Cystoisospora and Cyclospora have been linked to contaminated food and water, although Cyclospora is more frequently associated with food and waterborne sources. The first reported outbreaks of diarrheal illness associated with Cyclospora in the US occurred among employees and physicians in a Chicago hospital in 1990; stagnant water supplied to the physicians’ dormitory was implicated. Multiple outbreaks associated with contaminated foods, including berries, lettuce, snow peas, and basil, and water have been reported.