Life Cycle of the Protozoan Parasite Entamoeba Histolytica

Entamoeba histolytica, often written as E. histolytica, is a protozoan parasite which is thought to have infected as many as 50 million humans worldwide. Its life cycle does not make for comfortable reading.

Mature cysts – clusters of individual trophozoites encased in a tough capsule – survive outside their host in water or in soil, and on some foodstuffs. With a lifespan of several months, these E. histolytica cysts wait to be swallowed as part of some contaminated food or liquid by a human or other host (dogs and cats, as well as other primates, have also been shown to be susceptible to infestation by this protozoan parasite, according to the Entamoeba home page).

Having been ingested, the parasites excyst, releasing up trophozoites, the active stage in Entamoeba histolytica’s life cycle. On emerging from the cyst, a trophozoite with four nuclei will divide itself three times, and then each nucleus will divide itself once, so that a total of eight trophozoites are released into the new host’s digestive tract, resulting in invasive infections all over the host’s body.

The trophozoites migrate through the host’s body to the large intestines, where they ingest red blood cells, bore into intestinal walls, damaging the host’s tissue in the process, and multiply by binary fission.

At this stage, some of the trophozoites will go on to bore into the mucosal walls of the large intestine and invade the host’s bloodstream and major organs such as the liver, heart and lungs. Others will encyst themselves, encasing themselves in a capsule cyst with four nuclei and eventually being expelled from the host’s body in the form of fecal matter, beginning the cycle anew.

Although Entamoeba histolytica is a comparitively common parasitic infection, it can have serious consequences, including amoebic dysentery and liver abcesses, which can be fatal if left untreated. The parasites can also cause lesions on the intestinal walls as they bore into them, which can lead to digestive problems. Victims of an E. histolytica infestation can show symptoms such as dysentery, diarrhea, weight loss, fatigue and acute abdominal pains.

Like many parasites, E histolytica can be killed relatively easily through high temperatures or through freezing, and a simple precaution to avoid infection is to thoroughly cook any food which may be contaminated prior to consumption, as well as boiling water from unknown sources prior to drinking. Paromomycin, or Humatin, is the drug most commonly used to treat E. histolytica infections.