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10 : Cyclospora: Whence and Where to?
To the casual reader of the lay press and to the nonparasitologist, Cyclospora appears to have come "out of nowhere". A discussion of this apparently changing Cyclospora dynamic teaches about how new microbial threats to health are recognized and understood. Cyclospora was detected in fecal specimens from three unrelated individuals in Papua New Guinea in the absence of any other known diarrheal disease agents. The phylogenetic relationships between the human-associated Cyclospora and the Eimeria suggest that the former may also exhibit restricted host species range. Cyclospora is transmitted from person to person via ingestion of contaminated water and food. Water has been a consistently identified risk factor for cyclosporiasis in most regions of the world where Cyclospora is endemic, although it has rarely been detected in the incriminated water supply. Immunologically compromised hosts also appear to be at greater risk of disease from both Cyclospora and Eimeria, persons infected with human immunodeficiency virus (HIV) are well-represented among the reported cases of cyclosporiasis. The infectious dose of Cyclospora for humans is unknown. Estimates based upon well-characterized inocula in an epidemic setting indicate that as few as 10 to 100 oocysts may be sufficient. Many investigators have emphasized the utility of epifluorescence microscopy for improving the detection of the autofluorescent Cyclospora oocysts in rapid screening of fecal samples. Ultimately, a means of propagating the human-associated Cyclospora, a reliable and relevant disease model, and a system for genetic manipulation are required.