Gut Parasites

What is Cyclospora Cayetanensis?

Saskia Knight, Gut Health Nutritionist
Written by Saskia Knight, DipNT Published 20 January 2025
Sonia Khan, Pharmacist
Medically reviewed by Sonia Khan, Pharmacist Last reviewed 17 August 2026

Cyclospora cayetanensis is a tiny parasite that causes cyclosporiasis, an infection of the intestines. Its main symptom is watery diarrhoea that can last for weeks and sometimes months, and the symptoms often come and go just as you think you are recovering. Cyclospora spreads when people consume contaminated food or water and does not usually spread from person to person.

In the UK, infections are rare and almost always picked up abroad. Travellers to tropical and subtropical areas, particularly Central and South America, Southeast Asia and the Caribbean, are most at risk, and the UK’s best-documented outbreaks have been linked with travel to Mexico. If you are planning a trip, the NHS Fit for Travel service publishes guidance on Cyclospora infection for travellers.

How is it spread?

Cyclospora cayetanensis is most commonly spread by consuming food or water that contains the parasite’s oocysts. Oocysts are microscopic parasite 'eggs', and they are the infectious form of the parasite.

When a person swallows food or water contaminated with these oocysts, they 'hatch' in the intestines and release the active form of the parasite, which multiplies in the lining of the small intestine.

Freshly passed oocysts are not infectious straight away. They need days to weeks outside the body to mature (sporulate) before they can infect someone else, which is why the infection does not usually pass directly from person to person, and why outbreaks trace back to food and water rather than to contact with an infected person. A 2019 review in The Lancet Infectious Diseases sets out this unusual life cycle.

Cyclospora cayetanensis is spread through:

Contaminated food:

Imported fresh fruit, vegetables and herbs (classically berries, basil, coriander and salad leaves) can become contaminated during growing or washing, especially where crops are irrigated with untreated water.

In the UK, most reported infections are linked to travel or imported produce rather than locally grown foods.

Contaminated water:

Drinking untreated or contaminated water in high-risk regions can lead to infection.

Is Cyclospora found in the UK?

The parasite is not established in the UK, and the background risk here is low. A 2024 review that pooled 150 surveys from 42 countries, covering 166,611 people, found that about 3.4% of people tested worldwide carried Cyclospora, but only around 0.4% in high-income countries. Nearly all UK cases are in people who have recently returned from tropical or subtropical regions, including Central America, South America, Southeast Asia and the Caribbean.

The clearest UK pattern is a recurring one. In the summer of 2015, Public Health England and Health Protection Scotland investigated 176 confirmed Cyclospora infections in travellers returning from the Riviera Maya region of Mexico, 79 of them in the UK. The same early-summer wave returned in 2016 and again in 2017, when 78 UK cases had been reported by late July, largely in travellers who had stayed in holiday resorts in the same region. If you develop watery diarrhoea after a trip to Mexico or another high-risk area, tell your GP where you have been.

Before travelling to a high-risk area, it is worth reading the UK Health Security Agency’s advice for travellers on Cyclospora. This is public health guidance rather than a study, and it is written for exactly this situation.

What symptoms does Cyclospora cause?

The main symptom of cyclosporiasis is frequent, watery diarrhoea. In most otherwise healthy people the illness settles on its own, but it can drag on for weeks if untreated, and the symptoms may come and go (relapse) over time, a pattern described in a 2019 review by US food safety scientists.

Common symptoms:

When should you see a GP?

See your GP if you have recently visited a high-risk area and have any of the symptoms above. Tell them where you travelled, because travel history changes which infections the laboratory tests a stool sample for.

Persistent diarrhoea also matters in its own right. Short-lived diarrhoea is usually caused by viruses or bacteria; once it has lasted two weeks or more, parasites such as Cyclospora, Giardia and Cryptosporidium become more likely culprits, particularly after travel. A clinical review in JAMA puts persistent diarrhoea at around 3% of people travelling to lower-income countries.

Get medical advice promptly if you have any of the following:

  • Watery diarrhoea lasting longer than 7 days
  • Signs of severe dehydration, such as a dry mouth, passing little or no urine, or dizziness
  • Being unable to keep fluids down because of vomiting
  • Severe stomach pain or bloating
  • Blood in your stool, or black, tarry stools
  • Unexplained weight loss
  • A change in bowel habit that has lasted more than three weeks
  • New digestive symptoms starting over the age of 50, or a family history of bowel or ovarian cancer

Gut Parasites share many of the same common symptoms. If you suspect you have a parasite you should contact your GP; a home test is never a substitute for medical advice about the warning signs above.

Who is most at risk?

The UK is generally considered a low-risk area because the parasite is not established here. The people most at risk of infection are:

Travellers to high-risk areas such as Central and South America, Southeast Asia and the Caribbean, particularly people eating fresh produce and salads in resorts.

People with weakened immune systems, for example because of HIV or cancer treatment, who can have more severe or prolonged infections, sometimes with complications beyond the gut. If this applies to you, see a doctor early rather than waiting for the illness to pass.

How is it diagnosed?

Cyclosporiasis is confirmed with a stool test, which looks for the parasite’s oocysts or its DNA in a sample of faeces. The test identifies what is present; interpreting the result and making the diagnosis is a job for your doctor.

Oocysts are shed intermittently and may not appear in every sample, so doctors often ask for more than one stool sample over a few days.

How to test for Cyclospora cayetanensis

Laboratories can look for Cyclospora in several ways, including examining a stained sample under a microscope and DNA-based methods such as PCR (polymerase chain reaction) testing. A stool sample can be collected at home and sent to a laboratory, and in the UK the NHS route is through your GP, who can arrange stool testing if you have symptoms after returning from a high-risk country.

Our gut parasite test identifies 28 different types of parasites, pathogenic bacteria and viruses via an at-home stool sample test. A home test can tell you what was found in your sample; it does not diagnose any condition, and results need clinical interpretation.

How is it treated?

In most otherwise healthy people, Cyclospora eventually clears on its own, although that can take weeks, and the symptoms can return before they finally settle. Rest and plenty of fluids matter in the meantime, and a pharmacist can advise on rehydration.

Where treatment is needed, Cyclospora is unusual among gut parasites: the standard anti-parasitic medicines used for infections such as Giardia do not work against it. The antibiotic that does work is trimethoprim-sulfamethoxazole, known in the UK as co-trimoxazole, and even after treatment symptoms sometimes come back. It is a prescription-only medicine, and whether to treat, and with what, is a decision for your GP. This is one reason a proper diagnosis matters: a treatment aimed at the wrong parasite will not work.

What helps with recovery?

Gut parasites can cause gut dysbiosis, which is an imbalance of the bacteria within the gut microbiome, and that imbalance can bring unpleasant symptoms of its own. While your gut settles, some gentle habits may help:

High-fibre foods: fruits, vegetables, whole grains, nuts, legumes and seeds. Introduce fibre slowly and remember to drink plenty of fluids.

Fermented foods with live cultures: yoghurt, kefir, and fermented vegetables such as kimchi and sauerkraut may help support the balance of bacteria in your gut.

Avoid alcohol, caffeine, and greasy, sugary or spicy foods while you have symptoms, as they can make diarrhoea worse.

Read our guide on good gut foods for a full breakdown of foods that can help to improve your gut health.

Can it be prevented?

Cyclospora spreads through contaminated food and water. Sensible precautions reduce the risk, but there is no guaranteed way to completely prevent infection if you are exposed to the parasite.

Food safety hygiene:

Wash fresh produce thoroughly: rinse fruit and vegetables under running water before eating, even if you plan to peel them.

Avoid raw produce when travelling: in high-risk regions, avoid uncooked leafy greens, herbs and berries unless you are sure they have been safely prepared.

Cook food thoroughly: heat kills the parasite, so freshly cooked meals are safer.

Water safety:

Drink bottled or boiled water when travelling in high-risk areas.

Avoid adding ice cubes to your drinks.

Hygiene:

Wash your hands thoroughly with soap and water after using the toilet and before eating.

Avoid drinking from, or swimming in, untreated natural water sources such as lakes and rivers in high-risk regions.

For destination-specific food and water advice before a trip, check TravelHealthPro, the UK’s official travel health advice service. Like the UKHSA page above, this is guidance for travellers rather than research.

The role of gut health in recovery

Research suggests that the make-up of your gut bacteria may influence how a gut infection plays out, and that an infection can in turn unsettle that balance. Much of this work comes from laboratory and animal studies, so it is best read as promising rather than proven.

Screening a stool sample for parasites, alongside a wider look at the balance of your gut bacteria, can help you understand how your gut is doing as it recovers. No test can tell you whether you will catch an infection, and no home test diagnoses one.

This guide is for information only and does not replace medical advice. If your diarrhoea is persisting after travel, or you have any of the warning signs listed above, see your GP first.

Sources

Guidance rather than studies: the NHS Fit for Travel page on Cyclospora infection, the UK Health Security Agency’s advice for travellers on Cyclospora (GOV.UK), and TravelHealthPro destination advice, all linked above.

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Medically reviewed by Nutritionist Saskia Knight BA DipNT