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Life Cycle of Blastocystis Hominis

Blastocystis hominis is a microscopic parasite of the gastrointestinal tract. It's effect as a disease on humans is controversial. Many healthy people present with B. hominis in their digestive tract while others suffer from diarrhea, abdominal pain or other gastrointestinal symptoms. However, there is debate in scientific circles whether B. hominis actually causes infection or if it just harmlessly exists in the gastrointestinal system.

  1. Method of Infection

    • No one knows how people become infected with B. hominis, but oral-fecal contact is suspected. Many forms of protozoa enter the digestive system through contact with contaminated feces, as when someone's hands aren't washed thoroughly after using the toilet, then food is prepared by them. Infection with B. hominis does appear to be more prevalent in areas where there is poor sanitation and hygiene.

      The life cycle and means of transmission for B. hominis is still under investigation; therefore, this is a proposed life cycle.

    The Thick-Walled Cyst Stage

    • The thick-walled cyst stage exists in the stool and is thought to be transmitted by inadvertent oral contact with contaminated fecal material. Once ingested, the cysts will infect the epithelial cells on the intestinal tract.

    The Vacuolar Stage

    • The cysts will then reproduce asexually within the epithelial cell. Eventually, the cysts will rupture releasing multiple parasites in the form of vacuoles within the cell. These then either grow into a multi-vacuolar form or an amoeboid form of the organism.

    The Multi-Vacuolar Stage

    • The multi-vacuolar form of the parasite will then leave the infected cell and develop into a pre-cyst. This pre-cyst will them go through a process to form a thin-walled cyst. This cyst will then infect other epithelial cells in the intestinal tract and begin the life cycle again.

    The Ameboid Stage

    • The vacuolar form can also change into an amoeboid form of the parasite that will leave infected cells and reproduce through mitosis. Eventually, these will also form pre-cysts. This pre-cyst will then form a thick-walled cyst. This cyst will then exit the intestinal tract through feces and remain there until they are inadvertently ingested. Then the life cycle will begin again.

    Diagnosis and Treatment

    • Diagnosis can be accomplished by searching for cysts in a recently collected stool sample. Blood tests can also assist in diagnosing the illness by looking for specific antibodies or antigens. If you are asymptomatic treatment is unnecessary. Potential medications for treating B. hominis include metronidazole, sulfamethoxazole/trimethoprim and iodoquinol.

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