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Digestive Disorders > Lower Abdomen

Intestinal parasites – contagion, symptoms and treatment

Dr. med. André Sommer

Dr. med. André Sommer

Parasites are living things that survive at the expense of their host. Throughout human development, many parasites have specialized in survival in a human host. The gastrointestinal tract of humans in particular often serves as the entry point for these parasites. The intestine is easily accessible through food or contaminated drinking water. Which parasites often nest in the human gut? What are they? And how are infections with such parasites treated?

What types of parasites are there?

Parasites that affect humans are divided into three groups:

  • Protozoa (Protozoa)
  • Worms (Helminths)
  • Arthropods (Arthropods)

In addition, doctors differentiate whether the parasite is outside the human body (ectoparasites, e.g. lice) or inside the body (endoparasites, e.g. worms).

Worms and protozoa are the intestinal parasites with the greatest importance for humans. Because parasitic diseases (parasitosis) are rarer in Germany than in warmer and tropical regions, it is particularly important to take a detailed medical history of symptoms and to initiate appropriate examinations to identify and treat parasitic diseases.

What are the most common parasitic diseases of the intestine?

The most common parasitic diseases of the intestine are caused by worms and protozoa. From the group of worms, intestinal leeches (also “suction worms”), the group of roundworms and the so-called paired worms (also “flatworms”) play an important role. Among the unicellular organisms, amoebae, lamblia, cryptosporidia and blastocysts are among the most common pathogens.

Tip: The detection of parasites is often requested in the case of unclear digestive problems, but often does not provide any evidence, so that the complaints could be due to another cause. Nutritional therapy can alleviate the symptoms and improve quality of life. Therefore, as a first step, we recommend our therapy program, which is reimbursed by health insurance companies. Click here for more information.

1) Nematodes

The nematodes are a large group of parasites that can affect the human intestine. The main representatives of this group are

  • Pinworm (Enterobius vermicularis)
  • Roundworm (Ascaris lumbiricoides)
  • Whipworm (Trichuris truchiura)
  • Hookworm (Ancylostoma duodenale)

Pinworm (E. vermicularis)

It is assumed that around the world 200 million people are infected with E. vermicularis. It is the most common parasitic intestinal infection in humans. The worm, which can only be hosted by humans, attacks children especially often. The length of the worms is between six and twelve millimeters and is therefore very small.

The pinworm gets into the human body through contaminated food (unwashed fruit and vegetables) or through contact with contaminated material (toilets etc.) and can also be transmitted from person to person.

The worms are often noticed in the stool. They are white and are clearly visible through their meandering movements. The main symptom of infection with E. vermicularis is a severe itching that occurs in the anal region. In severe cases, it can lead to weight loss, urinary tract Infections or appendicitis.

The diagnosis of the disease is usually made by with an adhesive strip examination. With the help of an adhesive strip, a smear of the anus is obtained, which is examined under a microscope for the eggs of E. vermicularis.

Roundworm (Ascaris lumbiricoides)

Roundworms are most common in tropical regions. A. lumbiricoides infections are common in places with low hygienic standards. An adult roundworm can grow up to forty centimeters long. It survives in the intestine for up to two years. The eggs of the roundworm can be seen in a stool sample under the microscope, so the doctor can diagnose roundworm infection (ascariasis). Symptoms that can be triggered by roundworm infestation are nausea, vomit, weight loss and stomach pain.

Whipworm (Trichuris trichiura)

Adult whipworms are up to five centimeters long. Infection with these parasites is mainly limited to tropical regions. Most cases in Germany occur in people who have spent a vacation in a tropical country. Infection with the whipworm (trichuriasis) is diagnosed through the presence of worm eggs in the stool. Trichuriasis usually remains without symptoms. In rare cases it can lead to stomach pain, nausea and vomiting.

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Hookworm (Ancylostoma duodenale)

The name of this hookworm comes from the word for the human duodenum. Hookworms get into the body through the skin or contaminated food and nest there in the small intestine and duodenum. Hookworms that infest humans are rare in Germany. The dog hookworm, which is more common in Germany, cannot survive in the human body.

Infection with hookworms can lead to a loss of blood as the adult worms can consume up to thirty milliliters of blood per day. Those affected complain of fatigue and weakness. In addition, villi can be destroyed, resulting in severe stomach pain.

The doctor can detect a hookworm infection by the presence of eggs and larvae in the stool.

2) Intestinal fluke

Trematodes are also worms. You get them mainly by eating raw meat or raw fish. Infections with only a few intestinal flukes usually remain without symptoms and subside on their own. A more substantial infestation can lead to diarrhea, nausea, vomiting and stomach pain. An intestinal gel infestation is proven by the presence of eggs in the stool.

3) Blood flukes

Blood flukes (schistosomes) are rare in Germany. They occur primarily from ravel through Asia or Africa. The blood flukes can enter the body through the skin when bathing in contaminated water. Infection with blood flukes (schistosomiasis) begins in the liver. From there, they penetrate into other organs such as the intestine. Due to their characteristic appearance, schistosome eggs are easily detectable in the stool.

4) Unicellular organisms

Protozoa are another group of parasites that infect the human gut. Important representatives of these organisms are:

  • Amoeba
  • Lamblia
  • Cryptosporidium
  • Blastocysts

Amoeba (Entamoeba histolytica)

Amoeba pass into the body through contaminated water, unwashed fruit or vegetables. Infection with amoeba (amoebic dysentery) leads to severe diarrhea, often with the presence of blood or mucus, In addition, violent, cramping stomach pain can occur. Weight loss, fever and chills can also result from infection with E. histolytica. The doctor makes the diagnosis by detecting so-called amoeba cysts in the stool. The symptoms usually appear between one and four weeks after the infection. In some cases, however, amoeba dysentery only occurs years after the tropical trip.

Lamblia (Giardia lamblia)

Lamellia infections are mainly caused by poor hygienic conditions. The cysts enter the gastrointestinal tract through the mouth and multiply rapidly there. Typical symptoms of G. lamblia infection (giardiasis) are pain in the upper abdomen, diarrhea, nausea and vomiting. The pathogen is detected by microscopic examination of a stool sample.

Cryptosporidia (Cryptosporidium parvum)

Infection with cryptosporidia spreads from host to host, especially from infected pets, bovine and people. After infection with C. parvum (cryptosporidiosis), the pathogen is eliminated in large quantities with the stool. Abdominal pain and diarrhea occur over weeks, which usually heal on their own. So-called C. parvum oocysts can be detected in a stool sample.

Blastocysts (Blastocystis hominis)

Infection with B. hominis is often without symptoms. It is believed that up to 15 percent of the population suffer are infected. The pathogens spread mainly through contaminated food and contaminated water. If symptoms occur, it is usually mild diarrhea that subsides on its own. The pathogens can be detected in a stool sample under the microscope.

How are diseases with intestinal parasites treated?

Just as bacterial infections can be treated with antibiotics, there are many medications to treat parasitic infections, which are often grouped together as "antiparasitics". Most parasitic infections can be treated with a specific drug that works against the causative parasite.

Treatment of worm infections

With worm infections (worms = helminths) so-called "antihelminthics" are used. Mebendazole is an important representative of this group, which shows good effectiveness against roundworms. Praziquantel works against tapeworms and schistosomes.

Treatment of unicellular organisms

Infections with unicellular (Protozoa) are treated with "antiprotozoics". The group of antiprotozoics consists of very different drugs, all of which are directed against certain protozoa. Examples are furazolidone (for infections with G. lamblia) or metronidazole (with trichomoniasis).


Most parasitic intestinal infections occur rarely in Germany. The symptoms often include abdominal pain, nausea, vomiting and diarrhea. A parasitic intestinal infection should be considered, especially if such symptoms occur after a vacation in a warmer climate. Because the detection of pathogens or eggs in the stool makes them easy to diagnose, successful treatment can be initiated quickly.


Dr. med. André Sommer

Dr. med. André Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara Care.

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