Blastocystis is a common microscopic organism that inhabits the intestine and is found throughout the world. A full understanding of the biology of Blastocystis and its relationship to other organisms is not clear, but is an active area of research
What are the symptoms of infection with Blastocystis?
Watery or loose stools, diarrhea, abdominal pain, anal itching, weight loss, constipation, and excess gas have all been reported in persons with Blastocystis infection. Many people have no symptoms at all. The organism can be found in both well and sick persons.
How long will I be infected?
Blastocystis can remain in the intestine for weeks, months, or years.
Is Blastocystis spp. the cause of my symptoms?
The role of Blastocystis in causing disease is controversial among experts. Some types of Blastocystis may be more likely to be associated with symptoms. Finding Blastocystis in stool samples should be followed up with a careful search for other possible causes of your symptoms.
Is having blastocystosis common?
Yes. In fact, many people have Blastocystis in their intestine, some without ever having symptoms.
What should I do if I think I have blastocystosis?
See your health care provider who will ask you to provide stool samples for testing. Diagnosis may be difficult, so you may be asked to submit several stool samples.
Is medication available to treat blastocystosis?
Yes. Drugs are available by prescription to treat blastocystosis. However, sometimes medication is not effective, and a search for other possible causes of your symptoms may be necessary.
How did I get blastocystosis?
How Blastocystis is transmitted is not known for certain, although the number of people infected seems to increase in areas where sanitation and personal hygiene is not adequate. Studies have suggested that risk of infection may increase through:

• ingesting contaminated food or water,
• exposure to a day care environment, or
• exposure to animals.

How can I prevent infection with Blastocystis?

• Wash your hands with soap and warm water after using the toilet, changing diapers, and before handling food.
• Teach children the importance of washing hands to prevent infection.
• Avoid water or food that may be contaminated.
• Wash and peel all raw vegetables and fruits before eating.
• When traveling in countries where the water supply may be unsafe, avoid drinking unboiled tap water and avoid uncooked foods washed with unboiled tap water. Bottled or canned carbonated beverages, seltzers, pasteurized fruit drinks, and steaming hot coffee and tea are safe to drink.

Biology
Causal Agent
The taxonomic classification of Blastocystis hominis is mired in controversy. It has been previously considered as yeasts, fungi, or ameboid, flagellated, or sporozoan protozoa. Recently, however, based on molecular studies, especially dealing with the sequence information on the complete SSUrRNA gene, B. hominis has been placed within an informal group, the stramenopiles (Silberman et al. 1996). Stramenopiles are defined, based on molecular phylogenies, as a heterogeneous evolutionary assemblage of unicellular and multicellular protists including brown algae, diatoms, chrysophytes, water molds, slime nets, etc. (Patterson, 1994). Cavalier-Smith (1998) considers stramenopiles to be identical to his infrakingdom Heterokonta under the kingdom Chromista. Therefore, according to Cavalier-Smith, B. hominis is a heterokontid chromista.
Knowledge of the life cycle and transmission is still under investigation, therefore this is a proposed life cycle for B. hominis. The classic form found in human stools is the cyst, which varies tremendously in size from 6 to 40 μm . The thick-walled cyst present in the stools is believed to be responsible for external transmission, possibly by the fecal-oral route through ingestion of contaminated water or food . The cysts infect epithelial cells of the digestive tract and multiply asexually (, ). Vacuolar forms of the parasite give origin to multi vacuolar and ameboid forms. The multi-vacuolar develops into a pre-cyst that gives origin to a thin-walled cyst , thought to be responsible for autoinfection. The ameboid form gives origin to a pre-cyst , which develops into thick-walled cyst by schizogony . The thick-walled cyst is excreted in feces .