Blastocystis hominis is a microscopic parasite sometimes found in the stools of healthy people as well as in the stools of those who have diarrhea, abdominal pain or other gastrointestinal problems. Infection with blastocystis is called blastocystosis.
Researchers don’t yet fully understand the role that blastocystis plays, if any, in causing an infection. Certain subtypes of blastocystis may be more likely to cause symptomatic infection, or may pose a risk only when combined with other types of infection. In some cases, blastocystis simply resides in the digestive tract without causing harm.
Signs and symptoms that might be associated with blastocystosis include:
- Abdominal cramps
- Excessive gas (flatulence)
- Anal itching
- Loss of appetite
- Weight loss
When to see a doctor
See your doctor if you have signs and symptoms, such as diarrhea or cramps, that last longer than three days.
Once thought to be a harmless yeast, blastocystis is a parasite, a microscopic single-celled organism (protozoan). Many protozoans inhabit your gastrointestinal tract and are harmless or even helpful; others cause disease.
Whether blastocystis is the type of protozoa that causes disease is controversial. While many people who carry blastocystis have no signs or symptoms, the organism is also found in others who have diarrhea and other gastrointestinal problems. Because blastocystis often appears with other organisms, experts aren’t sure whether it causes disease on its own or is an innocent bystander in this setting.
It’s also possible that some people may be carriers of blastocystis and don’t exhibit any signs or symptoms of infection, while other people are more susceptible to infection.
Many types of protozoans get into the intestinal tract through oral-fecal contact, such as occurs when a person doesn’t wash his or her hands thoroughly after using the toilet before preparing food. No one knows for certain how blastocystis is transmitted, but experts suspect it’s through oral-fecal contact. Experts do know that the prevalence of blastocystis increases in places with inadequate sanitation and poor personal hygiene.
If you have diarrhea associated with blastocystis, it’s likely to be self-limiting. However, anytime you have diarrhea, you lose vital fluids, salts and minerals, which can lead to dehydration. Children are especially vulnerable to dehydration.
Information provided by, Mayo Clinic Staff.