Knowledge Transfer Task Force

Article 14 - Unraveling the cyclospora mystery

November 30, 2020

Related Resources:
Kniel - Analysis of the presence of Cyclospora in waters of the Mid-Atlantic States and evaluation of removal and inactivation by filtration
Lenaghan - Determination of physical and chemical mechanisms to prevent Cyclospora infection
Lopez - Cyclospora prevalence in irrigation water in fresh produce growing regions
Mattioli - Sources and prevalence of Cyclospora cayetanensis in Southeastern US water sources and growing environments

This article originally appeared in The Packer, and is reprinted here with permission. © 2020 The Packer

While the human race struggles under the siege of COVID-19, other pathogens continue to burden the American public as well. The last thing someone with COVID-19 or with a compromised immune system needs is to also become infected with a foodborne pathogen. 

Cyclospora cayetanensis is a public health challenge that is relevant to today’s fresh produce industry, and it is a mystery waiting to be solved.

Historically, U.S. doctors tested for the parasite if a patient suffered gastrointestinal symptoms after visiting a cyclospora-endemic country. Doctors didn’t conduct the test, however, if a patient had remained within U.S. borders, as cyclospora was not thought to be present here.

In recent years, the increasing frequency of cyclosporiasis outbreaks in the U.S. – many associated with domestic fresh produce – leaves us to wonder if the pathogen has been present here after all, undiscovered simply because it hadn’t been tested for.

Cyclospora attacks the human gastrointestinal system. While some infected persons experience no symptoms, others are not so fortunate, suffering severe diarrhea and other stomach-related symptoms.  While it is rarely deadly, it can require hospitalization.

Cyclospora has a biologically complex life cycle tied to its ability to infect humans.  Shed from human feces, cyclospora oocysts escape into the environment to mature and become transmissible again through the food we eat – mostly fresh produce – or the water we drink.  Oocysts are thought to require at least 1-2 weeks in favorable conditions to mature. (Luckily, direct person-to-person transmission is thus unlikely.)

Several details of how the parasite replicates and develops – and how it moves through the environment to contaminate food and water – are still unknown. 

Fresh produce may become contaminated with cyclospora when sewage and other domestic wastewater – treated or untreated – is discharged into surface waters that are subsequently used for crop irrigation.  For a useful illustration of cyclospora’s complex biology, check out this resource from the Centers for Disease Control and Prevention.        

Studying cyclospora and how to control it poses many challenges. For example, it can be hard to find a large enough environmental sample to DNA fingerprint it, and it cannot be cultured in a laboratory like other pathogens.

Because the cyclospora oocyst is thick-walled and much larger in size than viruses and bacteria, it has proven difficult to inactivate in agricultural water. It also survives exposure to chemical disinfectants currently used in produce packing/processing facilities.

2018 was a pivotal year, with two U.S. outbreaks resulting in more than 2,200 diagnosed cases of cyclosporiasis. One reason for that sharp increase may be due to the availability of new diagnostic devices like Biofire and Nanoporetech that perform rapid tests for multiple diseases in a lab or hospital setting. 

Notably, both of those outbreaks were associated with U.S.-grown produce; one involved broccoli, cauliflower and carrots, the other lettuce contained in salad mixes. 

In the summer of 2020, another outbreak that sickened 700 people led the Food and Drug Administration to test irrigation canals in Florida, where they detected cyclospora but haven’t been able to match it to the outbreak strain. 

Recognizing the threat this pathogen poses to fresh produce food safety, Center for Produce Safety has invested $2 million in produce-specific cyclospora research studies in recent years; several projects are underway now. 

One of those ongoing projects is led by the CDC’s Dr. Mia Mattioli. Mattioli comments that “the recent results of FDA’s investigation of the 2020 outbreak were the first evidence of cyclospora in the southeastern growing region and the first time produce grown in this region was associated with [illnesses].” 

Her research is evaluating cyclospora prevalence in produce growing environments of the Southeast.  With the University of Georgia, researchers will evaluate cyclospora in irrigation ponds and on fresh produce in the region, using packinghouse rinse water as a proxy.

The study will also test municipal wastewater sludge samples and on-farm porta-potties to better understand how the pathogen might be transmitted and thus better understand the potential for it to enter the growing environment. Mattioli is quick to point out that on-farm porta-potties are not currently suspected as a source of contamination of the growing environment because sanitation vendors typically follow regulations governing disposal of human waste.

So it’s still a mystery as to how a pathogen that is usually associated with human feces is getting onto fresh produce. 

We need to know what the key conditions are that allow cyclospora to flourish and persist in the produce growing environment.  What temperature, pH level and soil conditions support the pathogen’s two-week incubation period required for oocysts to sporulate and become infectious?

Could leaking septic systems and/or wastewater effluents containing the pathogen discharge into surface waters or seep into ponds or wells used for irrigating crops? On that question, a 2019 CPS-funded project led by Gerardo Lopez, Ph.D., University of Arizona, found low levels of cyclospora in Arizona irrigation canal water.

Researchers concluded that it is important to monitor human wastewater and nearby worker camps, as well as any intruding animals which could transfer the pathogen to fresh produce if they picked up the parasite from human waste or fecal-contaminated garbage.

Additionally, a CPS-funded study begun this year by University of Tennessee’s Scott C. Lenaghan, Ph.D., seeks to develop a model to forecast propagation of cyclospora oocysts to help explore control measures that could inactivate the pathogen in irrigation water.

His group is studying the effectiveness of gamma radiation, ultraviolet radiation, ozonation and chlorine dioxide gas, among other chemicals. 

Taking another angle, a study CPS funded this year led by Kalmia Kniel, Ph.D., of University of Delaware, is exploring the use of zero valent iron – essentially scrap iron fragments – to remove or inactivate the parasite in filtration-based systems.

Results of these exciting projects will enhance our industry’s knowledge about cyclospora and provide tools to help us mitigate the risks it poses to public health and to our industry’s livelihood. 

Additionally, several researchers are improving the typing, sampling and detection methods needed to study this pathogen.  Much more research is needed determine the prevalence and persistence of cyclospora, its life cycle as it moves between humans and the environment, and how best to trace outbreaks to their source.  

Vic Smith of JV Smith Companies, headquartered in Yuma, Ariz., and chairman of the CPS board of directors, sums up perfectly the value of CPS’s work to the fresh produce industry: “While much remains to be discovered about C. cayetanensis, CPS is helping our industry by quickly prioritizing our research needs, engaging world-class scientists to answer industry’s questions, and helping industry businesses to apply the resulting science proactively to their operations.” 


Doug Grant chairs Center for Produce Safety’s Knowledge Transfer Task Force and is a CPS board member; he is executive vice president and chief operating officer of The Oppenheimer Group.