Cyclosporiasis is an intestinal illness caused by Cyclospora cayetanensis, a one-cell parasite. The majority of cases are seen in the warmer months.In the last several years, outbreaks of the illness have been reported in the United States and Canada.yclosporiasis is an intestinal illness caused by Cyclospora cayetanensis, a one-cell parasite. The majority of cases are seen in the warmer months.