Friday, March 2, 2012

Entamoeba histolyica: A Deadly Amoeba



Introduction:
Entamoeba histolytica has become known as the more serious of the amoeba parasitic infections [1].  Clinically, this parasite causes the disease amoebiasis and the scientific name suggests that this parasite destroys the tissue of its host leaving them with severe diarrhea, also known as dysentery [1], as well as dehydration. In severe cases of infection, E. histolytica burrows through the large intestine and travels through the blood stream to the liver where it feeds and causes abscesses in the liver almost turning it into liquid [3]. It directly infects humans through food and drink that have come into contact with contaminated feces, or it can be spread by direct contact with contaminated feces.  There is no intermediate host for this parasite.  E. histolytica is found worldwide, but it is seen more prominently in tropical regions than elsewhere.  There are some humans who are more susceptible to get this parasite which is, but not limited to, homosexual males, frequent travelers, and institutionalized populations [2].


Symbiont Description:
The genus of this species is Entamoeba, and the species is histolytica.  E. histolytica lives and multiplies as a trophozoite, which is a growing stage in the life cycle of some sporozoan parasites, when they are absorbing nutrients from the host [4].  This oblong trophozoite can only survive within the host and fresh feces, after this stage of transmission the trophozoite becomes a cyst that can survive in soil, water, and on foods until it is consumed by the host. [3]


Host Description:
There is no intermediate host in this parasites life cycle.  E. histolytica only infects humans making it a hologenous parasite.  This parasite has been estimated to infect almost fifty million people worldwide [1].


Life Cycle:










Mature cysts pass from the large intestine through the host as feces. Once the host comes into contact orally with contaminated feces, the cysts are ingested and passed through the digestive system. Once in the small intestines, they transform back into trophozoites and migrate to the large intestine. The parasite lives and multiplies, by binary fission, within the large intestine. In severe infections, E. histolytica can break through the large intestine and travel to organs within the body via the blood stream. Once they come into contact with the blood stream, they attach to it and cause abscesses to form. [3]

Ecology:


E. histolytica is not specific to one region, but in industrialized nations they are known to infect immigrants, institutionalized people, and recent travelers [3]. It is easy to cure the minor infections of E. histolytica with two antibiotics: Metronidazole and Tinidazole [1,3]. As long as the symptoms do not become severe, it can be easily treated however if the infection becomes severe one might require surgery to relieve the excess fluid built up around the organ [1].


Example of a Shortened Life Cycle:
E. histolytica has shortened its life cycle compared to most parasites. By having only one host, Entamoeba histolytica does not have as many stages to go through and does not have to rely on certain hosts to reach sexual maturity.  [1]

References:
[1] Entamoeba histolytica info. (2012). Retrieved from http://entamoebahistolytica.org. Accessed February 27, 2012.
[2] Keas, A. (1999). Entamoeba histolytica. Retrieved from https://www.msu.edu/course/zol/316/ehisgeo.htm.
[3] Parasites in humans find the nastiest parasites in humans. (2010). Retrieved from http://www.parasitesinhumans.org/entamoeba-histolytica-amoebiasis.html

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