Parasites in the gut: worms, protozoa and Blastocystis

Healthy state

Intestinal parasites are organisms that live in the gut at the human’s expense. A distinction is made between single-celled protozoa such as Giardia, Cryptosporidium, amoebae, Blastocystis and Dientamoeba, and worms (helminths) such as pinworms, roundworms, whipworms, hookworms, tapeworms or threadworms (Strongyloides). Worldwide about one in four people (around 1.5 billion) carry roundworms, whipworms or hookworms, above all where sewage is not safely disposed of. An estimated 600 million people or more are affected by Strongyloides.

They are usually transmitted through contaminated water or food, through person-to-person smear infection or, for hookworms and Strongyloides, through larvae that enter through the skin of people walking barefoot. With the soil-transmitted worms, the eggs in stool are not yet infectious; they ripen in the soil for about three weeks, so there is no direct person-to-person infection here. The pinworm is different: its eggs are infectious quickly and spread via hands, bedding and dust. It mainly affects children of nursery and primary-school age and is common even in countries with good water supplies.

The gut defends itself in its own way. Against worms, the immune system mounts a response of its own (a type 2 response): mast cells Mast cells Immune cells beneath the skin and mucous membranes, filled with histamine and other messengers. They raise the alarm in allergies, infections and stress. More in the chapter “Mast cells: alarm cells in the gut, histamine and the disputed MCAS” and eosinophils, a kind of white blood cell, are activated, the lining makes more mucus and gut movement is stimulated to flush the worms out. Against Giardia, which attaches itself to the small-intestine lining, secretory IgA IgA (secretory IgA) The antibody of the mucous membranes. It is released into the gut in large amounts, where it holds germs in the mucus without causing inflammation. More in the chapter “IgA: the antibody that keeps the gut clean, and what vitamin A, D and omega-3 have to do with it” plays a role; in people lacking antibodies, Giardia infections often run a more stubborn course. A blood count can show raised eosinophils with worm infestation, a non-specific sign that allergies cause too.

Not every finding is a disease. Blastocystis is one of the most common single-celled organisms in the human gut and, depending on the region, is found in one fifth to over two thirds of people, often without symptoms. In several studies Blastocystis even went with a more diverse gut flora Microbiome, gut microbiota The community of all microbes in the gut, mainly bacteria, plus viruses, fungi and archaea. Most live in the colon. More in the chapter “Building microbial diversity” and was more common in healthy people than in people with bowel inflammation. Whether such co-residents are part of a healthy balance is open. All that is certain is that finding one is not a diagnosis.

Disrupted state: causes and effects

Giardia, Cryptosporidium and Entamoeba histolytica, for example, clearly make people ill. One to two weeks after the cysts are swallowed, Giardia causes diarrhoea with bloating, foul-smelling fatty stools, cramps and weight loss. Because it damages the surface of the small-intestine cells, milk sugar and fat can be digested less well for a while afterwards, and a lactose intolerance sometimes lasts for weeks. Giardia can also have long-lasting effects: after an outbreak in Bergen, Norway, six years later around 39 percent of those affected had irritable bowel and 31 percent chronic fatigue, clearly more than people who had not been infected. Both slowly declined over the years.

Cryptosporidium causes watery diarrhoea that begins after 2 to 10 days (about 7 on average) and lasts one to two weeks; people with healthy defences usually recover without treatment, and some have no symptoms at all. It becomes dangerous when defences are severely weakened, and the diarrhoea can then become chronic. The organisms are very resistant to ordinary chlorine, which is why they spread via swimming pools, paddling pools and drinking water.

The role of Blastocystis and Dientamoeba fragilis is disputed. For Blastocystis, some subtypes are more linked with symptoms, others more with health. For Dientamoeba, an analysis of over 27,000 stool tests found no link with symptoms, and in a placebo Placebo A dummy treatment without an active ingredient. Comparing with it shows how much a remedy achieves beyond expectation and chance. -controlled study in children, treatment brought no benefit.

Worms often make themselves felt differently from what you would expect. Pinworms mainly cause nocturnal itching around the anus. Hookworms feed on blood and in the long run lead to iron deficiency and anaemia, especially in young women and children. The fish tapeworm can use up vitamin B12. Threadworms (Strongyloides) can stay unnoticed in the body for decades after a stay in warm countries and become life-threatening under corticosteroids or other drugs that dampen the immune system.

An idea has also come out of worm infections: where worms are common, there are fewer allergies and inflammatory bowel diseases Inflammatory bowel disease Umbrella term for Crohn’s disease and ulcerative colitis: long-term, relapsing inflammation of the gut that needs medical treatment. More in the chapter “Immune system and inflammation”, probably because worms put the brakes on the immune system (the hygiene hypothesis). Trials with pig whipworm eggs in Crohn’s disease were based on this. In the largest study so far, with 252 adults, three doses brought no advantage over placebo. It follows that you should not acquire worms “for your health”, neither from the internet nor in a self-experiment.

Be wary of offers of a “parasite cleanse” and of tests that find parasites in almost everyone. Real parasites are detected with suitable stool tests, and treatment depends on the organism found.