Blastocystis is a microscopic single-celled organism that lives in the human gut and turns up on many stool tests.1Wikipedia. Blastocystis It is one of the most common gut organisms in the world, carried by more than a billion people.2PubMed Central. Commensal, pathogen, or passenger? Rethinking the role of Blastocystis in human health Finding it doesn’t settle whether it’s making you sick, and doctors still disagree about whether, and when, it needs treatment.3PubMed Central. Blastocystis: Consensus of treatment and controversies
What Kind of Organism Blastocystis Is
Blastocystis isn’t a bacterium, a virus or a worm. It is a single cell with a nucleus, a tiny organism known as a protist.4Wikipedia. Blastocystis Genetic work places it in the same broad group as algae, diatoms and water molds.5PubMed Central. Blastocystis: Taxonomy, biology and virulence Under a microscope it can look several ways, including a round form with a large central bubble, and a cyst form.6Wikipedia. Blastocystis The cyst is a tough resting stage that survives outside the body and passes the infection on.
Blastocystis comes in many genetic strain types, which labs call subtypes, written ST1, ST2, ST3 and so on.7PubMed Central. Epidemiological survey on prevalence and subtypes distribution of Blastocystis sp. in Southern Guizhou, China ST3 is often the most common in people, followed by ST1 and ST2.8PubMed Central. Subtypes and phylogenetic analysis of Blastocystis sp. isolates from West Ismailia, Egypt Some subtypes are mainly found in farm animals, such as ST5 in pigs and ST7 in poultry.9PubMed. Epidemiology of Blastocystis in farm animals: A review Subtyping is mostly a research tool, so your report will usually just say Blastocystis.
The name on that report can vary. You may see Blastocystis hominis, Blastocystis sp. or Blastocystis spp., and all of them mean the same organism. Older reports and some doctors still use “hominis,” which is an outdated name. On medical records the condition is sometimes called blastocystosis.
How common it is depends a lot on where you live. Rates are much higher in places with poorer sanitation, but carrying it is not a sign of uncleanliness or personal failure.
Does Blastocystis Cause Symptoms
Many people with Blastocystis have no symptoms at all.10CDC. Blastocystis Others with it in their stool report loose stools, belly pain, gas, constipation, anal itching or weight loss.11CDC. Blastocystis Infections can be silent, short-lived and symptomatic, or long-lasting with symptoms.12PubMed Central. Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection
Experts don’t agree on whether it is to blame. It was long dismissed as harmless, but some evidence points to harmful effects and some to protective ones.13PubMed Central. Commensal, pathogen, or passenger? Rethinking the role of Blastocystis in human health It may act differently depending on the person’s gut and strain type, rather than being simply good or bad.14PubMed Central. Commensal, pathogen, or passenger? Rethinking the role of Blastocystis in human health People who carry it also tend to have a more varied mix of gut bacteria.15PubMed Central. Colonization with the enteric protozoa Blastocystis is associated with increased diversity of human gut bacterial microbiota A diverse gut is usually seen as a healthy sign, which is one reason some experts see the organism as harmless.
People with IBS, which means long-term belly pain with changed bowel habits, are about twice as likely to carry Blastocystis.16PubMed. The role of Blastocystis sp. and Dientamoeba fragilis in irritable bowel syndrome: a systematic review and meta-analysis Yet the same strain types also turn up in people with no symptoms.17PubMed Central. Commensal, pathogen, or passenger? Rethinking the role of Blastocystis in human health So it may be a sign of an unsettled gut rather than its cause.18PubMed. Blastocystis subtypes and their association with Irritable Bowel Syndrome
Hives, rashes and itching have been reported in some carriers.19PubMed. Blastocystis, urticaria, and skin disorders: review of the current evidences In one comparison, though, chronic hives patients carried it only a little more often than healthy people, 21% versus 17%.20PubMed. Chronic urticaria associated with Blastocystis hominis infection In people with chronic hives who carried ST3, clearing the organism led to more remissions.21PubMed Central. The Eradication of Blastocystis spp. Subtype 3 Improves the Course of Chronic Spontaneous Urticaria
A positive test and your symptoms may simply be unrelated. Because many carriers feel perfectly well, you may have found it only because you had a stool test for another reason. Other parasites, bacteria, food intolerance and IBS cause similar symptoms, so ask your doctor what else the stool test checked for.
Some symptoms point elsewhere. Blood in the stool, fever, night sweats or major weight loss need prompt medical review. They aren’t typical Blastocystis signs and shouldn’t be explained away by it.
How Blastocystis Is Found on a Stool Test
The method your lab used matters. Looking at stained stool under a microscope missed about half of cases in one comparison.22PubMed Central. Comparison of Microscopy, Culture, and Conventional Polymerase Chain Reaction for Detection of Blastocystis sp. in Clinical Stool Samples A DNA-based stool test, often called PCR on reports, caught about 94% to 98%.23PubMed Central. Comparison of Microscopy, Culture, and Conventional Polymerase Chain Reaction for Detection of Blastocystis sp. in Clinical Stool Samples24PubMed. Detection of Blastocystis sp. in ulcerative colitis, Crohn’s and chronic diarrheal patients by microscopy, culture and real-time polymerase chain reaction So a negative microscope result doesn’t rule it out, while a positive one from either method is trustworthy. Labs can also grow the organism from stool in culture, which can detect more than a direct smear.25PubMed. Comparison of direct fecal smear microscopy, culture, and polymerase chain reaction for the detection of Blastocystis sp. in human stool samples
Reports usually name the method, such as ova and parasites, microscopy or PCR panel. If symptoms continue after a negative microscope test, ask whether a DNA test is possible. Results can also say how many organisms were seen, which some doctors use when deciding on treatment.
After treatment, a follow-up stool test is how clearance is checked. Use the same test type so the comparison is fair. Feeling better matters more than the test result.
Whether You Need Treatment
Doctors note that people with symptoms often improve without any treatment.26PubMed Central. Blastocystis: Consensus of treatment and controversies In children with symptoms, 40% were better within two weeks with no treatment at all.27PubMed. Clinical efficacy of Saccharomyces boulardii or metronidazole in symptomatic children with Blastocystis hominis infection Clear rules on when to treat don’t exist.28PubMed Central. Utilizing Probiotics for the Prevention and Treatment of Gastrointestinal Diseases Treating someone with no symptoms just because of a positive test is generally not recommended.
A sensible conversation with your doctor covers how long symptoms have lasted and how much they affect daily life, and whether other causes were tested. It also weighs possible drug side effects against an uncertain benefit, and considers whether to watch and wait for a few weeks first.
Treatment is more often chosen for people with persistent diarrhea or belly pain and no other explanation, and for people with chronic hives and no other cause found. Children with ongoing symptoms may also be treated, after a doctor’s assessment.
Waiting makes the most sense when symptoms are mild, steady or improving, and nothing alarming such as blood in the stool is present. If symptoms are getting worse, affecting eating, school or work, or causing weight loss or dehydration, waiting is not the right approach and you should be seen sooner. During the wait, a simple note of what you eat, your stool pattern and your symptoms gives your doctor something concrete to judge at the next visit.
Metronidazole as the Usual First Treatment
Metronidazole, an antiparasitic antibiotic, is the drug most often prescribed for Blastocystis.29PubMed Central. Update on the pathogenic potential and treatment options for Blastocystis sp A typical adult course is 250 to 750 mg three times a day for 10 days.30PubMed Central. Update on the pathogenic potential and treatment options for Blastocystis sp In children, 30 mg per kg twice daily for 10 days was used and cleared the organism in most within a month.31PubMed. Clinical efficacy of Saccharomyces boulardii or metronidazole in symptomatic children with Blastocystis hominis infection
Results vary widely. Reported success ranges from none to nearly all patients.32PubMed Central. Resistance towards metronidazole in Blastocystis sp.: A pathogenic consequence In one group of heavily infected adults, it cleared the organism in only 4 of 12.33PubMed. Blastocystis hominis and the evaluation of efficacy of metronidazole and trimethoprim/sulfamethoxazole The cyst form can withstand the drug, and low drug levels in the gut may even let the organism grow faster.34PubMed Central. Resistance towards metronidazole in Blastocystis sp.: A pathogenic consequence So finish the whole course as prescribed rather than stopping early.
Common side effects are a metallic taste and nausea. Tell your doctor about other medicines you take. Symptoms may ease within days or take weeks, and some people feel worse briefly from side effects. Report any numbness or tingling in your hands or feet to your doctor.
Alcohol is the big caution. Drinking while on metronidazole can cause flushing, a pounding heart, vomiting and severe nausea. The caution continues for a few days after the last dose because the drug takes time to leave the body. Alcohol can also hide in places people forget, such as some liquid cold medicines and mouthwashes, so check labels during the course. If you accidentally drink some, stop drinking and seek medical advice if symptoms are severe.
Other Treatment Options
The antibiotic trimethoprim-sulfamethoxazole (TMP-SMX), also sold as Bactrim or Septra, has shown good results.35PubMed. A Systematic Review about the Efficacy of Antiparasitic Agents in the Treatment of Blastocystis Species Nitazoxanide, another antiparasitic, has also worked in some patients.36PubMed Central. Update on the pathogenic potential and treatment options for Blastocystis sp In lab tests, strain types responded better to TMP-SMX and ivermectin than to metronidazole.37PubMed Central. In Vitro Antimicrobial Susceptibility Patterns of Blastocystis Even so, standard drugs and combinations have failed to clear it in some patients.38PubMed Central. Update on the pathogenic potential and treatment options for Blastocystis sp
The probiotic yeast Saccharomyces boulardii relieved symptoms in about 94% of children after a month, versus 73% with metronidazole.39PubMed. Clinical efficacy of Saccharomyces boulardii or metronidazole in symptomatic children with Blastocystis hominis infection Both cleared the organism equally well, about 93% to 94%.40PubMed. Clinical efficacy of Saccharomyces boulardii or metronidazole in symptomatic children with Blastocystis hominis infection Some probiotic bacteria reduced Blastocystis in lab dishes, though this is not yet proven in people.41PubMed Central. Utilizing Probiotics for the Prevention and Treatment of Gastrointestinal Diseases
S. boulardii is sold over the counter, but check with a doctor for children or anyone with a weak immune system. The evidence comes from one trial in children. It may suit people who want to avoid antibiotics.
A second attempt usually means a change. Doctors often switch drug rather than repeat the same one, and sometimes two drugs are combined. A follow-up stool test checks the result.
TMP-SMX is a sulfa drug, so anyone with a past allergy or rash to sulfa medicines should tell the doctor before it is prescribed. Common side effects include nausea and rash. A rash that appears during the course should be reported rather than ignored, since occasionally it can be serious. It is usually taken with plenty of fluids, and it can interact with some other medicines, so give your doctor a full list of what you take. It isn’t suitable for everyone, such as people in early pregnancy or with certain kidney problems, which is part of why doctors pick the drug case by case.
Why Treatment Sometimes Fails
Metronidazole resistance has been reported for decades.42PubMed Central. Resistance towards metronidazole in Blastocystis sp.: A pathogenic consequence Different strain types respond differently to the same drug.43PubMed Central. Update on the pathogenic potential and treatment options for Blastocystis sp Reinfection is common where exposure continues.44PubMed Central. Resistance towards metronidazole in Blastocystis sp.: A pathogenic consequence If symptoms persist after the organism is cleared, it probably wasn’t the cause.
After a failed course, retest to see whether the organism is still present. If it is gone and symptoms remain, look for other causes such as IBS or food intolerance. If it is present, ask about switching drugs. If reinfection seems likely, check household members or pets.
If the organism was never cleared, the follow-up test would be positive soon after treatment, which points toward resistance or the hardy resting form surviving. If it shows up again after a negative test, that can be reinfection, especially if the source of exposure is still there. Failure calls for a different drug, while reinfection calls for finding and removing the source. A household member carrying the same organism can pass it back, so one person’s treatment can be undone by someone who was never tested.
How People Catch Blastocystis
It spreads when cysts from feces are swallowed. In one village where nearly all residents were infected, rivers contaminated by poorly kept septic tanks carried it.45PubMed Central. Blastocystis sp.: waterborne zoonotic organism, a possibility? Siblings shared the same strain type, pointing to person-to-person spread.46PubMed Central. Blastocystis sp.: waterborne zoonotic organism, a possibility? People working closely with pigs, cattle or other animals have higher rates.47PubMed Central. Blastocystis sp.: waterborne zoonotic organism, a possibility? Pig manure fertilizer was a likely source in farming communities.48PubMed Central. Zoonotic Transmission of Blastocystis Subtype 1 among People in Eastern Communities of Thailand: Organic Fertilizer from Pig Feces as a Potential Source Chickens carry it often, while dogs and cats rarely do.49PubMed Central. Prevalence, Subtype Distribution and Zoonotic Significance of Blastocystis sp. Isolates from Poultry, Cattle and Pets in Northern Egypt Everyday exposures include untreated water and raw produce in areas with poor sanitation, changing diapers or caring for an infected family member, and farm visits where livestock are handled without washing hands afterward.
How to Avoid Getting It Again
Cysts survived chlorine at all doses tested.50PubMed. The impact of chlorine, ultraviolet-C, and microwave treatment on the survivability of Blastocystis sp. cysts Killing them needed chlorine far stronger than the up to 5 ppm used in drinking water.51PubMed Central. Resistance of Blastocystis to chlorine and hydrogen peroxide In risky areas, boil water or use a filter designed to remove parasites rather than relying on chlorine tablets.
Wash your hands with soap after the toilet, diaper changes and handling animals. Wash or peel produce, especially if manure fertilizer may be used. Wear gloves when gardening with animal manure, and avoid swallowing river or lake water.
Boiling is the most dependable method for water. Bringing it to a rolling boil for a minute is generally accepted as enough, or three minutes at high altitude. Filters vary widely, so look for one rated to remove parasites by its pore size and testing claims rather than assuming any filter works. Bottled water from a sealed, trusted source is a reasonable alternative when you can’t boil or filter.