Cyclospora: An Elusive Emerging Pathogen

Most of us food microbiologists are really bacteriologists and feel incapable of working with viruses or parasites. At least I feel that way! For that reason, I’ve tried to avoid having to deal with Cyclospora, but with almost 2,300 domestically acquired, presumably food-related cases last year, it’s worthy of attention. The most concerning issue with Cyclospora is not the nature of illness it causes; while unpleasant, it’s generally not life threatening, and we’re not currently aware of long-term sequalae. The main problem with Cyclospora cayetanensis is that, compared to other foodborne pathogens, we know essentially nothing about it, except that humans are the only host.

A little background: Cyclospora cayetanensis is truly an emerging pathogen, with the first U.S. outbreak associated with Guatemalan raspberries less than 25 years ago. Historically, cases have been associated with foreign travel; however, in recent years, there have been many domestically acquired cases. Until last year, on the rare occasions when a food vehicle could be identified, imported fresh produce was the culprit. Last year represented the first time the pathogen was detected in U.S.-grown produce, and it happened more than once.

Two major outbreaks were identified last year: one associated with romaine lettuce, the other with fresh vegetables. However, illnesses epidemiologically related to these outbreaks accounted for only about a third of the roughly 2,300 cases of domestically acquired illnesses last year. The cause of the other two-thirds is unknown, partly due to our limitations in typing this organism. Fresh Express, a major leafy green processor implicated in one outbreak, assembled a Blue Ribbon panel which has published an interim report and a corresponding fact sheet in an attempt to raise awareness and offer suggestions to address this unusual pathogen.

Doing whole genome sequencing (WGS) on a eukaryote is much more complicated than applying the technique to bacteria. To date, WGS and other typing approaches are still in development. The organism has a complicated life cycle, requiring a week or two outside the host to morph into an infectious form. At this point, researchers debate how to determine if the organism is actually alive and viable, if it is infectious, how long it remains infectious once sporulated, and other basic information.

We are clearly in our infancy in understanding this pathogen. The lack of typing means we cannot distinguish multiple, concurrent outbreaks based on characteristics of the organism. There is a complete reliance on epidemiology to try to discern different outbreaks. Infected individuals begin showing symptoms roughly one week after exposure. Because the illness is not particularly severe (and the organism is not considered to cause a serious adverse health consequence [i.e., SAHCODHA hazard]), people may be unlikely to seek medical attention, delaying the recognition of an outbreak.

Very few researchers study this pathogen, and even fewer are in academia. Most research is being conducted by FDA and CDC, and the Center for Produce Safety, which is largely industry funded, has awarded several research grants to better understand the prevalence of in U.S. waterways.

Because humans are the only known host (so far), the obvious mitigation is preventing contact between human feces and fresh produce. In the absence of more information, the produce industry will continue to implement Good Agricultural Practices, such as handwashing and appropriate servicing of portable toilets. But unlike other organisms transmitted via the fecal-oral route, the one- to two-week life cycle required to become infectious means that direct contact (e.g., lack of handwashing) is unlikely to cause illness. And since Cyclospora is resistant to chemical treatment, who knows how spores may travel through and persist in the environment? This begs the question: Is fresh produce really the only vehicle for cyclosporiasis? The burden of illness won’t decrease until we invest in developing the tools needed to answer some pretty basic questions.