Crohn's disease appeared after a trip to Colombia

Who is Jim, and what happened after his trip?

A healthy swimmer who loved to travel

Jim was a perfectly healthy 36-year-old swimmer who had never had gut symptoms. The only time his stomach had bothered him, as far as he could remember, was a gastroenteritis at the age of nine. He loved surfing and travelling around the world, and his last trip was to Colombia. Before leaving, he had the recommended yellow fever vaccine, without any side effects.

Bites, a moving swelling and a small change in stool

He came back from Colombia after 15 days, and the only incident he could remember was being bitten by many mosquitoes during an excursion inland. A few days later he noticed a swelling in his lower abdomen. The swelling kept moving, until his testicles swelled as well. It lasted about a week and then went away on its own.

The only reason Jim saw a doctor was a slight change in the shape of his stool. The gastroenterologist ordered several blood tests and found a raised CRP, which was raised again ten days later. Then he ordered a calprotectin test, which came back at 880 and showed strong activation of white blood cells. A colonoscopy confirmed the diagnosis, showing a picture of Crohn's disease that certainly did not match the lack of gut symptoms. Jim started prednisone and mesalazine, and two months later he came to the practice where I work as a scientific collaborator.

Following his course was hard, because Jim had no symptoms at all. This is rare, but I have seen it before. He had just finished his first treatment and was asked to repeat calprotectin. The value was much better, at 336, but still not normal. I decided to take it a step further.

Which clues pointed beyond Crohn's disease?

During his trip, Jim had been exposed to a completely different diet. That may not be enough to bring an autoimmune disorder to the surface. In a person who is already predisposed, however, genetically or through the environment, such a violent change of the microbiome could do it.

How are parasites linked with inflammatory bowel disease?

Some protozoa and worms are linked with the main immune-mediated gut conditions, including celiac disease, IBD and IBS, and some can change the host's immune responses.⁴ Whether they drive the disease or simply find a good place to live in an inflamed gut is not yet clear.

What did his stool tests show?

The lack of beneficial bacteria was clear, and so were the two other inflammation markers besides calprotectin, eosinophil protein X (EPX) and secretory IgA. The most striking finding, though, was a large number of Blastocystis hominis, both cysts and active forms. In addition, several strains of Citrobacter were found in very large amounts.

How was Jim treated?

Parasites are hard to clear. Despite the usual view, protozoa such as Blastocystis hominis are often not cleared by metronidazole alone. A recent systematic review found reports of resistance and treatment failure, and in some studies metronidazole even increased the number of viable parasites.³ Repeated antiparasitic courses within a few months are more effective, as long as every other part of the disease is covered at the same time.

In this case, the large number of gram-negative bacteria (Citrobacter) called for antibiotic treatment at the same time, at least during the first antiparasitic course. A third medicine suited this case as well, budesonide, because the large number of activated eosinophils, probably caused by the parasites, needed to be calmed.

A clear colonoscopy

In Jim's case, budesonide was first given after the first month of antibiotic treatment, and that is when he felt much better. His urgency disappeared and his stools became completely formed. Finally, vitamin D was given until his blood level rose above 60 (63.3). Jim was able to stop prednisone without relapse, and he stayed on mesalazine with budesonide at intervals, as decided by his gastroenterologist. His last colonoscopy was clear, without any sign of relapse, and he feels less tired. Every case is different, so Jim's plan describes his care and is not a plan for anyone else.

Infographic

1. 1

   Diet shift

   In several cases, a sudden shift in diet changes the microbiome a lot and may bring a predisposition to autoimmunity to the surface.

2. 2

   Look-alike infections

   Parasitic infections can mimic inflammatory bowel disease, both in symptoms and in tests.

3. 3

   Parasites and IBD

   Some parasites are found more often in people with IBD. Whether they drive the disease is not yet clear.

4. 4

   Stool findings

   In this case, stool tests showed many Blastocystis hominis, very large amounts of Citrobacter and signs of eosinophil activation.

5. 5

   Hard to clear

   Metronidazole alone often does not clear Blastocystis. Repeated courses worked better when the bacteria and eosinophils were treated too.

6. 6

   The outcome

   In this case, the last colonoscopy was clear, without any sign of relapse.

Sources: Gaulke et al. 2018, Mohammadi et al. 2015, Ulusan Bağcı et al. 2025.

gutpathways.com

Save this infographicImage 4:5, with sources, from gutpathways.com

What does Jim's case show about parasites and Crohn's disease?

• ▲ Parasites are found more often in people with IBD, but whether they play an important role in how the disease progresses is not clear.⁴
• ▲ People usually feel better after metronidazole, but other parts of the infection, such as eosinophil activation, also need attention.
• ▲ People with a history of autoimmunity, or at high risk of IBD, should keep in mind that travel to countries with a very different cuisine changes the microbiome.
• ▲ Gut symptoms after trips to tropical countries should be checked as soon as possible.
• ▲ This case supports the idea that IBD always appears together with a disturbed gut microbiome.