Cyclospora species as a cause of diarrhoea in humans

Within the past 10 years, the coccidian parasite Cyclospora cayetanensis has been clearly recognised as a cause of protracted diarrhoea in humans. Heavy infection results in inflammation and epithelial injury in the duodenum and jejunum. Of the multiple symptoms, diarrhoea may neither be the presenting nor predominant one. Following an incubation period of 12 hours to 11 days, the abrupt onset of watery diarrhoea occurring in a relapsing cyclic pattern is characteristic, lasting from six to eight weeks in immunocompetent patients, but three months in the immunocompromised. Of worldwide distribution, it is endemic in certain regions where it can be associated with rainy seasons. Outbreaks or isolated cases may also occur in developed countries. Contaminated water can transmit the oocysts, and usual control procedures for potable water supplies fail to detect the parasite, which resists chlorination. Diagnosis depends upon laboratory investigations, usually faecal microscopy. For reliable detection of characteristic oocysts in the faeces, special procedures may be necessary. Trimethoprim-sulphamethoxazole is established as the treatment of choice and leads to rapid relief of symptoms, although relapse in immunocompromised patients may require secondary prophylaxis.