This article is part of my series, The Pathogen Files. Each file contains key facts about one foodborne pathogen or microbial toxin, to keep you up to date (or refresh your memory) and help you do better at your job.
Cyclospora – a growing food safety threat
What you need to know about Cyclospora
The information below is part of an article I first published in 2024. It is mostly sourced from a presentation by Michelle Danyluk, University of Florida, delivered at the International Association of Food Protection Annual Meeting (2024).
Cyclospora infection is a foodborne and waterborne illness caused by Cyclospora cayetanensis, a single-celled parasite (technically, a coccidian protozoan). In wealthy countries, it was rare until recently, and only seen in people who had travelled to tropical developing countries, where the parasite is endemic.
However, since the 1990s, Cyclospora infections have been seen commonly in wealthy countries as well as developing countries.
Cyclospora infections take around one week to develop and cause symptoms. The illness can last from a few days to more than a month. Symptoms include watery diarrhoea, bloating, flatulence, burping, abdominal pain, cramps, nausea, vomiting, loss of appetite, body aches, fatigue, and fever.
The most common food sources for Cyclospora infections are fresh produce such as leafy greens, salad mixes and fresh basil. In the United States, Cyclospora outbreaks were only linked to imported produce prior to 2018. However, after 2018 there started to be many cases of Cyclospora in people who had not travelled internationally, and at least some of these cases were presumed to be from domestically grown food.
I say ‘presumed’ because Cyclospora cannot be cultured in the laboratory and is not suitable for genetic subtyping, making it very difficult to link food samples and environmental samples with infected people.
How does Cyclospora cause foodborne illness?
Humans are considered the only reservoir for Cyclospora cayetanensis, and asymptomatic infection is common in people in some tropical developing countries.
Cyclospora is transmitted when infected human faeces contaminate food or water. It is not transmitted directly from person to person because it is not infectious until one to two weeks after being passed in a bowel movement. The infectious agent is the oocyst of the parasite (a sort of ‘egg’), which is excreted in the faeces of an infected person. The parasite forms the oocysts while living inside its human host.
After leaving its host’s body, the oocyst sporulates (‘hatches’). The sporulated oocysts cause illness when ingested in food, such as raw leafy greens, or perhaps in contaminated water.
Little is known about the biochemistry of Cyclospora oocysts, or their sporulation process. It’s not even known whether they sporulate while on food crops or elsewhere, such as in soil or water. Nor is it known how many oocysts survive in the environment, how long they survive on crops, whether they are killed by solar radiation, or how easy it is for them to cross-contaminate from soil or water onto food. It’s also not known whether they can be physically removed from food plants such as leafy greens.
Fortunately, thorough cooking inactivates Cyclospora oocysts.
It is thought that Cyclospora oocysts get onto food plants such as leafy greens through direct contact with contaminated hands – such as from farm workers – or from contact between contaminated irrigation water and crops. However, the transmission process from irrigation water to crops is unknown.
Irrigation water cannot easily be monitored for the presence of Cyclospora oocysts because they are very difficult to detect in water, and the methods used for recovering oocysts from environmental samples are often questioned, with a lack of consensus in the science community around the methodology.
Agricultural water treatment chemicals in common use have limited efficacy against Cyclospora.
How big is Cyclospora as a food safety problem?
We don’t have a lot of data about how many people are asymptomatically carrying Cyclospora at any given time, or how many oocysts people shed when infected. We also don’t know what the infectious dose is for Cyclospora.
This makes it difficult to understand how much of a risk it poses within food supply chains. However, case numbers in the United States appear to be on the rise, with some scientists now considering it endemic in the U.S.
Other scientists suggest that the increased effectiveness of clinical tests may be the reason for the sudden apparent increase in domestically acquired cases in wealthy countries.
Controls for Cyclospora
Some experts suggest we could solve the problem of Cyclospora by eliminating it entirely from the population, while others say we should prevent its spread using food safety controls.
Unfortunately, once the oocysts get onto food, it is difficult to know whether they are present, due to a lack of easy detection methods, and as mentioned previously, there are no known ways for removing them from food that is intended to be eaten raw.
Because it cannot grow or replicate outside the human body, prevention of Cyclospora must focus on keeping human faeces away from food and water. As Dr. Danyluk said of finding the source of contamination in Cyclospora outbreaks, the key is to… Focus on the poop 💩💩💩
Main source: Presentation by Michelle Danyluk, University of Florida, from a session titled Root Cause Analysis for Non-cultivable Foodborne Pathogens at IAFP 2024.
This is an extract of an article that first appeared in Issue 248 of The Rotten Apple