Wednesday, February 29, 2012

Trypanosoma cruzi: The Kiss of Death







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Introduction:
Trypanosoma cruzi is a flagellar protozoan [2], which causes Chagas disease in humans. Humans are infected with T. cruzi when they come in physical contact with the carrier of the disease, the reduviid bug. Chagas disease is also known as American Trypanosomiasis and it infects about 16-18 million humans. Chagas disease causes the highest disease burden in Latin America [1].


Symbiont Description:
T. cruzi is from the phylum Sarcomastigophora; the class Zoomastigophora; the genus Trypansoma; and Species cruzi [3]. These flagellar organisms only have one nucleus and organelle. These asexual organisms reproduce by binary fission. T. cruzi lives one stage of their lives in the blood or tissues of vertebrate hosts and another stage in the intestines of their invertebrate vector [2]. T. cruzi are blood-dwelling protozoa, therefore they are considered trypanosomes. The trypomastigote form is an elongated cell (about 20 µm long) with flagella on the outer part of the membrane [1].


Host Description:
As stated above, T. cruzi chooses an invertebrate as its vector and a vertebrate for its definitive host. The reduviid bug, Panstrongylus megistus, also known as the kissing bug, is the main vector for T. cruzi to choose. Other insect types are used as its vectors, but 80% of Chagas disease cases are from the kissing bug. Other than these hosts, T. cruzi uses many different types of animals for reservoirs such as marsupials, rodents, primates, and several types of mammals  [1].

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Life Cycle:
When the kissing bug feasts on human’s blood, infected metacyclic trypomastigotes are left on the human’s skin through the feces of the insect. When the human scratches around the puncture site from the insect, the human is exposed to the trypomastigotes from the feces. When human cells are invaded, the trypomastigotes become amastigotes then they are released into the blood. Here, they develop back into trypomastigotes where the insect vector obtains them through the human skin in a blood meal. In the insect’s intestines, T. cruzi undergoes binary fission and migrates towards the rectum. This is so the parasite can be released through the insect’s feces onto the skin of the next human during the insect’s blood meal [4].


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Ecology:
            Chagas disease is endemic in Mexico, Central, and South America. Thriving in poor housing conditions, the vector of T. cruzi, the kissing bug, will pose a higher threat of infecting humans in those conditions. Therefore humans with poor living conditions in endemic countries have a greater risk of becoming infected with the T. cruzi parasite [4]. Symptoms of having Chagas disease range in three different stages: acute, indeterminate, and chronic stages. Rashes, fatigue, fever are just a few of the possible symptoms seen in the acute stage. The indeterminate stage is asymptomatic, occurs about 10 week after infection, and may last for several years. The chronic stage occurs 10-40 years post-infection and its symptoms include heart and intestinal problems that very likely lead to death [1].




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An example of:
           T. cruzi is an example of the direct correlation between social status and parasitic infestations. The lower the social status of a person, the more exposure there is to these parasites due to poor hygiene, nutrient sources, and housing or living conditions. The vector of T. cruzi, the kissing bug, is found in the walls and roofs of poorer built houses such as ones with mud walls or thatched roofs. Where these housing conditions are present, the vector of the parasite can survive, therefore allowing the parasite to continue to thrive. Eradication of these types of houses in poorer countries would lower the number of thriving kissing bugs and overall lowering the number of parasitic infestations of T. Cruzi [5].



Sources
[1] Schneider, Jeremy, and Claire Nordeen. "Trypanosoma cruzi." Parasites & Pestilence: Infectious Public Health Challenges. Stanford University, 2007. Web. 28 Feb 2012. <http://www.stanford.edu/class/humbio103/ParaSites2006/T_cruzi/index.htm>.

[2] "Trypanosoma cruzi." The Kiss of Death: Chagas' Disease in the Americas. University of Texas at Arlington, 2012. Web. 28 Feb 2012.<http://www.uta.edu/chagas/html/biolTcru.html>

[3]"Taxonomic Classification." Explore and Learn: Parasites. Brian E. Keas, 1999. Web. 28 Feb 2012. < https://www.msu.edu/course/zol/316/tcrutax.htm>

[4] "Parasites-American Trypanosomiasis." Centers for Disease Control and Prevention. USA.gov, 02 Nov 2010. Web. 28 Feb 2012. <http://www.cdc.gov/parasites/chagas/biology.html>.

 [5] Combes, Claude. Parasitism: The Ecology and Evolution of Intimate Interactions. Chicago: The Univeristy of Chicago Press, 2001. 290. Print.

1 comment:

  1. Very nice post, impressive. its quite different from other posts. Thanks for sharing.

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