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What is Blastocystis? Once thought to be a harmless yeast, Blastocystis hominis a microscopic single-celled protozoal parasite. It behaves like a tiny animal — hunting and gathering other microbes for food—one reason why having a balanced gut flora is important. Healthy gut floras do not support large amounts of parasites. Many protozoa inhabit your gastrointestinal tract and are harmless; others cause disease.

Protozoa-Blastocystis 1

Blastocystis lifecycle chart

Common Sources of Infection–Water     

Blastocystis hominis in culture

Blastocystis hominis in culture

Symptoms of Blastocystis: Common symptoms attributed to B. hominis infection are diarrhea, abdominal cramps, and nausea; and in more acute cases, profuse watery diarrhea and fever. Other possible associated symptoms include fatigue, anorexia, flatulence, and other gastrointestinal effects. It may or may not be a cause of “traveller’s diarrhea.” Some other symptoms reported are an itchy anus (common with several types of parasitic infections,) the presence of white blood cells in feces, rectal bleeding, increase in the number of eosinophils (a type of white blood cells), enlarged liver and / or spleen, rashes, itching, and joint pains and swelling. Blastocystis patients develop a chronic itchy sometimes non-healing red rash which waxes and wanes with gastrointestinal symptoms.  These lesions did not respond to topical antibacterial treatment or hydrocortisone treatment. 

Treatment of Blastocystis: Metronidazole and trimethoprim sulfa drugs.

Prevention of Blastocystis: Many types of protozoa get into the intestinal tract through oral-fecal contact, such as occurs when a person who doesn’t wash hands thoroughly after using the toilet prepares 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 blastocystosis increases in places with inadequate sanitation and poor personal hygiene.