Since 1996, the parasite Cyclospora cayetanensis has caused spring outbreaks of foodborne diarrhea in North America with eerie regularity. Frequently, it has been identified after sickening large groups of people who ate together at weddings and other events, or in residential facilities.
On June 2 and 3, 2010, Canadians learned Cyclospora was back for another year. This time it struck people who had attended the Big Sisters Chef’s Challenge in Sarnia, Ontario. The hors d’oeuvres tasting event, held on May 12, is thought to be the source of illness for at least 70 people, with eight cases confirmed as of June 4.
What is Cyclospora cayetanensis?
Cyclospora cayetanensis is a coccidian parasite related to Cryptosporidium and Toxoplasma gondii. A single-celled protozoan, it arrives on contaminated produce or in water, and multiplies in the small intestine, causing diarrhea of variable severity. The illness is known as cyclosporiasis.
Typical symptoms of cyclosporiasis include diarrhea, which can return after seeming to get better, cramps, and occasionally vomiting. Victims often feel fatigued, and the infection can take weeks to resolve on its own. Fortunately, cyclosporiasis can be treated with antibiotics.
Isolating the Source of Cyclospora
The source of the parasite in the 2010 Sarnia outbreak is likely to be elusive because the nature of the event – an hors d’oeuvres tasting charity fundraiser – means that people sampled many different foods. In addition, a relatively long incubation time of 10 to 14 days, plus additional time required for laboratory identification of the organism means that samples of perishable produce used at the event are long since gone.
Past outbreaks of cyclosporiasis have been traced back to imported raspberries, mesclun, basil, and snow peas. The link to raspberries was confirmed four years after it was first suspected when C. cayetanensis DNA was detected in a raspberry-cream filled wedding cake. This resulted in restrictions on the import of raspberries from Guatemala at certain times of year, but the parasite continues to arrive on other produce.
Investigators in Sarnia may be lucky enough to confirm the source if cases turn up from other events or venues where fewer types of fruits and vegetables were eaten.
How Does Cyclospora Get on Fruit and Vegetables?
The parasitic oocysts that sickened guests at the Sarnia Lambton Big Sisters event likely got deposited on fruit or vegetables in contaminated water. Cyclospora is not immediately infectious when passed in diarrhea as unsporulated oocysts, therefore it is not spread directly from person to person. Instead, it must continue development somewhere in the environment – possibly in water.
When crops are irrigated with contaminated water that contains the maturing oocysts and the produce is then eaten raw, the parasite is passed on. It’s also possible that farm workers handling produce with contaminated hands deposit immature oocysts that then mature in transit. It’s not clear why the parasite usually appears in spring but is relatively uncommon, at least in North America, during the rest of the year.
Spring outbreaks of cyclosporiasis have baffled public health workers in Canada and the United States since 1996. The immediate source of the parasite is often elusive, as is the environmental reservoir that results in contamination of fruit and vegetables.
Sources:
“Hiawatha Cleared in Cyclospora Incident.” Standardbred Canada June 3, 2010.
Ho, Alice Y. , Lopez, Adriana S., Eberhart, Michael G. et al. 2002 “Outbreak of Cyclosporiasis Associated with Imported Raspeberries, Philadelphia, Pennsylvania, 2000.” Emerging Infectious Diseases 6:6
“Outbreak of Cyclosporiasis Associated with Snow peas – Pennsylvania, 2004.” MMWR Weekly Sept 17, 2004.
Roberts, Larry S. and John Janovy Jr. Foundations of Parasitology 6th ed. Boston: McGraw Hill, 2000.
Rosemary Drisdelle - Rosemary Drisdelle has been published many times as a nonfiction writer and several times as a poet. Her first book, Parasites: Tales of ...
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