Cyclospora – An Elusive Intestinal Parasite Hiding on Raw Produce


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Cyclospora invades intestinal tissue and multiplies. Immature oocysts pass out in the stool. Image courtesy of the US CDC.

Cyclosporiasis does often respond to antibiotic treatment; however, receiving the right drug depends on accurate laboratory identification of the parasite.

One of the mysteries of C. cayetanensis is where it survives between human hosts, and whether any animals harbour and spread it.

Oocysts passed in human stool are in an unsporulated, or immature, stage, and must develop to sporulated oocysts before they can infect another human.

Thus, the infection is not passed directly from one person to another… but researchers don’t fully understand just which environmental conditions favor sporulation, and how infective oocysts get back to fresh produce.

Cyclospora After the 1996 Outbreak

In 1996, suspicion fell first upon strawberries from California, then turned to raspberries imported from Guatemala. The difficulties encountered in identifying the contaminated food were much the same then as they are today in Iowa: suspect food items are those typically consumed by many people, and the long time period between infection and the start of symptoms (one to three weeks) make the job of isolating commonly-consumed foods nearly impossible.

The evidence for contaminated raspberries in 1996, and similar outbreaks in the years that followed, led to import restrictions on Guatemalan raspberries, but Cyclospora wouldn’t be that easy to banish. Subsequent outbreaks implicated herbs, greens, and other fresh vegetables, typically imported and eaten raw. And in 2013, a paper by Dixon et al, published in the Journal of Food Protection, reported finding C. cayetanensis oocysts on produce grown in the United States and Canada as well.

Where Did the 2013 Cyclospora Originate?

The 2013 outbreak in Iowa and Nebraska is typical in many ways: it struck in late spring and early summer, raw fresh produce of some kind is the likely source, and the exact source remains elusive. It may never be determined.

Whatever the type of produce, it may have been contaminated in the field, perhaps with irrigation water, or during harvest, packaging, or transport. And while we’d like to think that happened far away, where food safety standards aren’t so rigid, we can’t be certain that that is the case. Cyclospora is evidently expanding its range, and until we understand how, and how to prevent it, these outbreaks will continue to occur.


Ashford, R. W. Occurrence of an Undescribed Coccidian in Man in Papua New Guinea. (1979). Annals of Tropical Medicine and Parasitology. 73:5.

Dixon B, Parrington L et al. Detection of Cyclospora, Cryptosporidium, and Giardia in Ready-to-Eat Packaged Leafy Greens. (2013). Journal of Food Protection 76:2

Drisdelle, Rosemary. Parasites: Tales of Humanity’s Most Unwelcome Guests. (2010). University of California Press.

Iowa Department of Public Health. Iowa Cyclospora Outbreak 2013 : Outbreak Update. 7.15.13 Accessed July 15, 2013.

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