Blastocystis hominis infection
Blastocystis hominis infection
Blastocystis hominis (B. 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 B. hominis is called blastocystosis.
Researchers don't yet fully understand the role that B. hominis plays in causing an infection. Certain subtypes of this parasite may be more likely to cause infection, or may pose a risk only when combined with other types of infection. In some cases, the parasite simply resides in the digestive tract without causing harm.
There are no proven treatments for Blastocystis, and the infection usually clears up on its own. However, if signs and symptoms don't improve, your doctor may recommend trying medications.
Signs and symptoms that might be associated with blastocystis include:
When to see a doctor
Once thought to be a harmless yeast, B. hominis is a parasite, a microscopic single-celled organism (protozoan). It behaves like a tiny animal — hunting and gathering other microbes for food. Many protozoa inhabit your gastrointestinal tract and are harmless; others cause disease.
Whether B. hominis is the type of protozoa that causes disease is controversial. While many people who carry B. hominis have no signs or symptoms, others have diarrhea and other gastrointestinal problems. Because B. hominis often appears with other organisms, experts aren't sure whether B. hominis causes disease on its own.
It's possible that some people are susceptible to illness caused by B. hominis infection, while others carry the parasite without signs or symptoms.
Many types of protozoa 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 B. hominis is transmitted, but experts suspect it's through oral-fecal contact. Experts do know that the incidence of infection associated with B. hominis increases in places with inadequate sanitation and poor personal hygiene.
Blastocystosis is common, and anyone can get the infection. You may be at higher risk if you travel where sanitation is inadequate or where the water may not be safe.
If you have diarrhea associated with B. hominis, 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.
Preparing for your appointment
You're likely to start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to an infectious disease specialist or a gastroenterologist.
Because appointments can be brief, it's a good idea to be well prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.
What you can do
Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out.
For blastocystis, some basic questions to ask your doctor include:
In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment.
What to expect from your doctor
What you can do in the meantime
If no oral rehydration solutions are available, you can make your own by combining 1 quart (about 1 liter) of bottled or boiled water with 8 level teaspoons (about 40 milliliters) of table sugar and 1 level teaspoon (about 5 milliliters) of table salt.
Anti-diarrheal medications aren't generally recommended, because they can make some diarrheal illnesses worse.
Tests and diagnosis
The cause of your diarrhea may be difficult to diagnose. Even if B. hominis is present on a fecal exam, it may not be causing your symptoms. Your doctor likely will take your medical history, ask you about recent activities, such as traveling, and perform a physical exam. A number of lab tests help diagnose parasitic diseases and other noninfectious causes of gastrointestinal symptoms:
Treatments and drugs
If you have blastocystis without signs or symptoms, then you don't need treatment. Mild signs and symptoms may improve on their own within a few days.
Potential medications for treating blastocystis include the antibiotic metronidazole (Flagyl), the combination medication sulfamethoxazole and trimethoprim (Bactrim, Septra, others), and the antiprotozoal medication iodoquinol (Yodoxin, others). However, keep in mind that response to medication for B. hominis infection varies greatly from person to person. And, because the symptoms you're having might be unrelated to blastocystis, it's also possible that any improvement may be due to the medication's effect on another organism.
You may be able to prevent blastocystis or other gastrointestinal infection by taking a number of precautions while traveling in high-risk countries.
Watch what you eat
Don't drink the water
If it's not possible to buy bottled water or boil your water, bring some means to purify water: Consider a water-filter pump with a microstrainer filter that can filter out small microorganisms. Look in camping stores for a filter that is certified by the National Science Foundation.
Another approach is to chemically disinfect water with iodine or chlorine. Iodine tends to be more effective, but reserve it for short trips, because too much iodine can be harmful to your body. You can purchase iodine tablets or crystals at camping stores and pharmacies. Be sure to carefully follow the directions.
Take precautions against passing a parasite to others
Last Updated: 2010-07-31
© 1998-2014 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "Mayo Clinic Health Information," "Reliable information for a healthier life" and the triple-shield Mayo logo are trademarks of Mayo Foundation for Medical Education and Research.
Terms and conditions of use