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Blastocystis hominis infection


Disease: Blastocystis hominis infection Blastocystis hominis infection
Category: Infectious diseases

Disease Definition:

A microscopic parasite found in the stools of healthy people, as well as those who have diarrhea, abdominal pain or other gastrointestinal problems is called B. hominis (Blastocystis hominis). However, researchers are not sure if it actually causes an infection or it simply lives in the digestive system harmlessly.

Treatment won't be necessary if someone has Blastocystis hominis in their stools without any signs of infection. Sometimes, even if the person doesn't show symptoms, Blastocystis hominis infection goes away on its own. However, If symptoms don't disappear, the patient may be prescribed medications. Yet, the drugs used to treat Blastocystis hominis infections aren't always efficient.

Work Group:

Symptoms, Causes


Some of the signs and symptoms that a blastocystis infection may cause include:


  • Diarrhea
  • Nausea
  • Fatigue
  • Bloating
  • Anal itching
  • Abdominal cramps
  • Excessive gas (flatulence)

If a person experiences diarrhea, cramps and fatigue that last longer than 3 days, they should see a doctor because these are the symptoms that are associated with a blastocystis infection.


In the past, B. hominis was thougth to be harmless yeast. It’s fully known now as parasite, a microscopic single-celled organism (protozoan). It hunts and depends on other microbes for food. These protozoa live in a person's digestive tract, and although some of them may end up causing a disease, but most of them are harmless.

Until now, studies didn’t show whether B. hominis is a harmful type of protozoa. In most cases of Blastocystis hominis, people don’t show symptoms. Some others who have this parasite experience diarrhea and other symptoms. Yet, Blastocystis hominisis associated with other organisms may be the real reason behind those symptoms. Scientists still don’t know whether B. hominis is the cause of the disease or merely a signal of other causes of diarrhea. Additionally, some people may be more susceptible to the infection, while others may carry the parasite without showing any signs or symptoms.

Experts suspect that B. hominis is transmitted through oral-fecal contact, such as when someone doesn't wash their hands thoroughly after using the toilet and then prepares food; however, nobody knows exactly how B. hominis is transmitted.
Even though it’s still a mere anticipation, but experts do know that the infection associated with Blastocystis hominis grow in places with improper sanitation and poor personal hygiene.



Whenever someone has diarrhea, they lose vital fluids, minerals and salts, leading to dehydration. Children are especially susceptible to dehydration. Even though the diarrhea associated with Blastocystis hominis is usually self-limited, but it could still cause dehydration.


The reason behind a person's diarrhea might not be diagnosed. Their medical history could be checked, recent events such as travelling could be reported and the doctor might ask the patient to do a physical exam.  Some of the lab tests that are helpful in diagnosing parasitic diseases are:

Stool (fecal) exam:

Known as ova and parasite test, this test looks for any parasite or its eggs (ova) that cause symptoms like diarrhea, cramping and bloating. Several stool samples are taken, each in a different day. The doctor will give the patient a container with preservative fluid for their sample. If not, the person can refrigerate their sample until it is taken to the lab, however, they should be careful not to freeze it.


If the cause of diarrhea is not evident in the sample test, the patient may be suggested endoscopy. A tube is inserted into the person's mouth or rectum to find out the cause but the person will have to fast the midnight before the test and be tranquillized during the test.

Blood tests:

Though B. hominis might not show in a blood test, but a person may be recommended to check if there is no other cause of the signs. When the body is under attack of a parasite, the immune system tries to fend off the infection. This event leaves antibodies and/or parasite antigens in the blood. Examining a sample of blood for those antigens or antibodies may detect some parasites.


Swelling or scarring an internal organ might be caused by the parasite. In order to detect the swelling or scarring, a person may be recommended X-rays, magnetic resonance imaging (MRI) or a computerized tomography (CT).


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