Intestinal worms (worm eggs, tapeworms, pinworms)

Worms (helminths) are multicellular parasites that can live in the human gut. They are detected in stool: by molecular genetics using PCR, which picks up the genetic material of tapeworms, roundworms, pinworms (oxyurids), hookworms, dwarf tapeworms, whipworms and threadworms, or by microscopy for worm eggs and larvae. Single-celled gut parasites such as Giardia, Cryptosporidium or Blastocystis are not worms; they are examined with the parasite PCR and described on their own pages. Because worms do not shed their eggs evenly, stool is often examined from several days.

Which worms occur in the gut

The most common worms in Central Europe are pinworms (Enterobius vermicularis), especially in children; they are passed on via eggs from hand to mouth. Beef and pork tapeworms (Taenia) enter the gut via raw or undercooked meat, the dwarf tapeworm (Hymenolepis nana) directly from person to person. Roundworms (Ascaris) and whipworms (Trichuris) are taken up via eggs from contaminated soil, vegetables or water. Larvae of hookworms (Ancylostoma and Necator, the “New World hookworm”) and threadworms (Strongyloides) penetrate the skin, for example when walking barefoot on damp ground. These species are found mainly in warm regions and in Germany are detected mostly after stays there.

What happens when worms settle in the gut?

Most worms do not multiply in humans; how heavy the infestation is depends on how many eggs or larvae were taken up. A few worms often cause no symptoms. Female pinworms migrate to the anus at night and lay their eggs there – this leads to itching, restless sleep and, through scratching, to renewed uptake. Hookworms attach to the small-intestinal lining and take up blood; with heavy infestation this results in iron deficiency. Whipworms anchor themselves in the colon lining and can trigger inflammation with mucus and blood. Roundworm larvae migrate through the lungs, which can cause a temporary cough; many adult roundworms compete for nutrients. As an exception, threadworms can multiply within the body and remain for decades.

How the body responds to worms in the gut

Against worms, the immune system switches to a distinct form of defence controlled by type 2 helper cells. Messengers such as interleukin-4, -5 and -13 increase eosinophil granulocytes and IgE antibodies, make the goblet cells produce more mucus and make the gut muscles work harder – the aim is to detach the worms and expel them. This is why eosinophils in the blood count are often raised with worm infestation, especially while larvae migrate through tissue. Tapeworms and pinworms, which stay inside the gut, often trigger this response only weakly. With weakened defences, for example under cortisone, the threadworm can multiply heavily and spread throughout the body.

No worms detected – what does it mean?

Without detection by PCR and microscopy, infestation with the worms tested for is unlikely. One limitation concerns pinworms: their eggs are laid on the skin around the anus and are therefore often not found in stool; here an adhesive tape sample taken in the morning is used in addition. Detection can also be missing shortly after infection, as long as the worms are not yet adult and do not lay eggs. Visible worm parts in stool, such as tapeworm segments, can be recognised independently of the laboratory test and are taken into account in the interpretation.

The interpretation is given in your report.