Parasites (gut)

Gut parasites can cause complaints that resemble irritable bowel and are therefore examined alongside other findings with persistent bowel complaints. Blastocystis hominis and Dientamoeba fragilis are frequently found alongside persistent bowel complaints – but just as often in people without complaints; their significance as pathogens is disputed. Giardia lamblia causes acute and chronic malabsorption. PCR diagnostics are considerably more sensitive than classical microscopy.

Which parasites occur in the gut

Gut parasites fall into two large groups. Single-celled organisms (protozoa) such as Giardia, Cryptosporidium, Cyclospora and Entamoeba multiply in the gut itself, so that a few pathogens taken up can become very many. Worms (helminths) such as pinworms, roundworms or tapeworms, by contrast, mostly do not multiply in humans; their number depends on how many eggs or larvae are taken up. Location matters too: Giardia, Cryptosporidium and Cyclospora colonise the small intestine, where nutrients are absorbed; Entamoeba, Blastocystis and Dientamoeba live in the large intestine. For Blastocystis and Dientamoeba, it is disputed whether they cause complaints at all.

How gut parasites affect the mucosa and the immune system

Parasites in the small intestine mainly damage the villi: the absorptive surface shrinks, digestive enzymes of the lining are lost, and watery diarrhoea, fatty stools and nutrient gaps are more likely. Parasites that attack the wall of the large intestine, on the other hand, trigger inflammation with mucus or blood in the stool. The immune response differs as well: against single-celled organisms, mainly T cells, interferon-γ and secretory IgA are at work. Against worms, the body switches to a defence using eosinophil granulocytes, IgE antibodies and increased mucus production intended to flush the worms out of the gut – which is why eosinophils in the blood tend to rise with worm infestation rather than with single-celled organisms.

What happens when parasites multiply heavily in the gut?

How heavily single-celled organisms multiply depends mainly on immune defence; with weakened defences, infections can last a long time and be severe. Dense colonisation displaces parts of the bacterial flora, loosens the gut barrier and makes demands on nutrients: certain tapeworms take up vitamin B12, and hookworms cause blood loss and thus iron deficiency. Many carriers nevertheless have no complaints. After intestinal infections have passed, studies have observed an increased frequency of persistent irritable bowel complaints; persistent low-grade inflammation, increased mast cells in the gut wall and heightened sensitivity of the gut nerves are being investigated as mechanisms.

The interpretation is given in your report.