Blastocystis hominis

Blastocystis hominis

Blastocystis hominis (B. hominis) is a single-celled parasite found in the large intestine. B. hominis has different forms because the parasite can look empty and resemble a yeast cell, or it can be filled with granules. The parasite forms cysts and can therefore survive outside the body for a long time. There are different types of B. hominis; 17 have been identified in the Netherlands. Of the people in the Netherlands who become infected with this parasite, approximately half are infected with types 3 and 4. It is still unclear whether certain subtypes cause more symptoms. A remarkable phenomenon is that B. hominis is often found together with another intestinal parasite: Dientamoeba fragilis. Testing for both parasites is recommended. B. hominis is very common in humans and animals. Laboratory research shows that 48% of people with intestinal complaints carry B. hominis.

Blastocystis hominis: Testing and diagnosis

For the diagnosis, the genetic technique Polymerase Chain Reaction (PCR) is used to detect B. hominis. A piece of DNA specific to this intestinal parasite is extracted from the stool. This piece is multiplied many times and can then be measured. The result of that measurement is expressed in cycles. If B. hominis is detected in the DNA between 16 and 35 cycles, then the parasite is present.

Risk factors for infection with Blastocystis hominis

A person becomes infected with this parasite only through contact with the stool of an infected person. Children are often infected because they have intensive physical contact with one another and frequently put objects, such as toys, in their mouths. If a partner or other family members are infected, it is important to have the other people involved tested as well. The presence of B. hominis causes symptoms more often in people with a weakened immune system and chronic conditions such as liver cirrhosis, diabetes, cancer, AIDS and leukemia.

Treatment of a Blastocystis hominis infection

If an infection with B. hominis causes symptoms, treatment can be chosen. In that case, the other family members are also tested and, if infected, treated as well. Even if the intestinal parasite does not cause symptoms in them, treatment is recommended in order to reduce the risk of reinfection. If medication is chosen, the use of Flagyl is discouraged. Flagyl does damage the parasites, but is often still unsuccessful. The chance of successful treatment with medicines such as clioquinol is fairly small (approximately 50%). This chance may increase when following a low-starch diet.

Do not treat
The symptoms can decrease considerably by following a low-starch diet. Treatment is then not necessary. B. hominis can ferment starch and produce gases that cause abdominal bloating and flatulence. A low-starch diet often reduces the symptoms. Following such a diet is therefore often sufficient. If you have no symptoms from an infection with B. hominis, treatment is not necessary. Following a low-starch diet is then enough. If you are infected, it is important to pay attention to hygiene, because you can infect others.

Prevention

Blastocystis hominis, like other parasites, is transmitted through contact with stool. Because the parasite can survive outside the body for a long time, good hygiene is very important. See also: hand washing and hygiene measures.

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