Amoebiasis: Difference between revisions

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a stool sample in 1875 by Fredor Losch. Throughout the world, amoebiasis is the second leading cause of death from a parasitic disease with an estimated 50 million cases per year and 100,000 deaths per year. However, most of these cases occur in the developing world.  Although it is the second leading cause of death from parasitic diseases, about 90% of the people exposed to  
a stool sample in 1875 by Fredor Losch. Throughout the world, amoebiasis is the second leading cause of death from a parasitic disease with an estimated 50 million cases per year and 100,000 deaths per year. However, most of these cases occur in the developing world.  Although it is the second leading cause of death from parasitic diseases, about 90% of the people exposed to  
<br><i>E. histolytica</i> are asymptomatic or report very mild symptoms.  
<br><i>E. histolytica</i> are asymptomatic or report very mild symptoms.  
[Image:Ehistdisp_cyst_wtmt.jpg‎|thumb|300px|right| <br><i>E. histolytica</i> cyst stained with iodine on a concentrated wet mount.]]


<br><i>E. histolytica</i> secretes proteinases that do considerable damage to its host. They can dissolve the tissues of the host by killing the host cells on contact; the cells become immobile and soon they will lose their cytoplasmic granules and structures. Finally, the nucleus of the cell will disintegrate. The proteinases can also engulf the red blood cells of the host.
<br><i>E. histolytica</i> secretes proteinases that do considerable damage to its host. They can dissolve the tissues of the host by killing the host cells on contact; the cells become immobile and soon they will lose their cytoplasmic granules and structures. Finally, the nucleus of the cell will disintegrate. The proteinases can also engulf the red blood cells of the host.
For those that do experience the symptoms associated with the Entamoeba histolytica infection, the onset is variable; they can occur gradually or very quickly. Gradual symptoms most often include a slow onset of colitis, or inflammation of the colon. Associated with colitis is diarrhoea and abdominal pain. Diarrhoea usually begins mildly and develops into diarrhoea that contains blood and mucous. Other signs of colitis are nausea, headache, and sometimes fever in less than forty percent of individuals. On the other hand, symptoms that occur quickly and intensely include semi liquid stools that contain blood and mucous. Abdominal pain can range from mild to severe, frequently accompanied by a tender liver. Rarer progressions of the disease include brain abscesses.  
For those that do experience the symptoms associated with the Entamoeba histolytica infection, the onset is variable; they can occur gradually or very quickly. Gradual symptoms most often include a slow onset of colitis, or inflammation of the colon. Associated with colitis is diarrhoea and abdominal pain. Diarrhoea usually begins mildly and develops into diarrhoea that contains blood and mucous. Other signs of colitis are nausea, headache, and sometimes fever in less than forty percent of individuals. On the other hand, symptoms that occur quickly and intensely include semi liquid stools that contain blood and mucous. Abdominal pain can range from mild to severe, frequently accompanied by a tender liver. Rarer progressions of the disease include brain abscesses.  
[[Image:Ehistdisp_cyst_wtmt.jpg‎|thumb|300px|right|Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.]]


<br><b>Prognosis</b>
<br><b>Prognosis</b>
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While existing in the cyst stage of its life cycle,<br><i>E. histolytica</i> tend to have a diameter of 10–15μm and are round in shape. Within a refractile wall containing chitin, are four nuclei, glycogen, and chromatoid bodies (ribosomal assemblies). As a trophozoite, <br><i>E. histolytica</i> are generally larger, of around 10 to 50μm in diameter. Unlike in the cyst form, the trophozoites are capable of moving spontaneously, gaining the energy for this process through anaerobically converting glucose and pyruvate to ethanol. Trophozoites can reproduce by binary fission  
While existing in the cyst stage of its life cycle,<br><i>E. histolytica</i> tend to have a diameter of 10–15μm and are round in shape. Within a refractile wall containing chitin, are four nuclei, glycogen, and chromatoid bodies (ribosomal assemblies). As a trophozoite, <br><i>E. histolytica</i> are generally larger, of around 10 to 50μm in diameter. Unlike in the cyst form, the trophozoites are capable of moving spontaneously, gaining the energy for this process through anaerobically converting glucose and pyruvate to ethanol. Trophozoites can reproduce by binary fission  
   
   
Once ingested by a human or a non-human primate, who are the natural hosts to the parasite, the <br><i>E. histolytica</i> cysts travel to the small intestine and become trophozoites in either the terminal ileum or colon (each cyst will produce eight trophozoites).  Cysts can exist outside the human body for long periods of time (from days or even up to months in damp conditions and ideal temperatures), Unlike cysts, trophozoites cannot survive outside of this preferred environment, and will degrade very quickly if exposed to an outside environment. The incubation period of the amoeba can vary from a couple of days to as long as a year.  Nonetheless, once in the small intestine, the trophozoites will attack the intestinal epithelial cells of the gastrointestinal tract. Not only do they invade the gastrointestinal track, but trophozoites can also migrate to other organs of the body and cause infection there as well. Once in the colon of its host, the trophozoites will encyst again and exit the body through the stool.
Once ingested by a human or a non-human primate, who are the natural hosts to the parasite, the <br><i>E. histolytica</i> cysts travel to the small intestine and become trophozoites in either the terminal ileum or colon (each cyst will produce eight trophozoites).  Cysts can exist outside the human body for long periods of time (from days or even up to months in damp conditions and ideal temperatures), Unlike cysts, trophozoites cannot survive outside of this preferred environment, and will degrade very quickly if exposed to an outside environment. The incubation period of the amoeba can vary from a couple of days to as long as a year.  Nonetheless, once in the small intestine, the trophozoites will attack the intestinal epithelial cells of the gastrointestinal tract. Not only do they invade the gastrointestinal track, but trophozoites can also migrate to other organs of the body and cause infection there as well. Once in the colon of its host, the trophozoites will encyst again and exit the body through the stool
 
[[Image:PROTFIG40.jpg‎|thumb|300px|right|<br><i>E. histolytica</i> trophozoite measured at 40 micrometers in length from a patient with moderate diarrhea ]]
<br><b>Treatment</b>
<br><b>Treatment</b>


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"E. histolytica contains proteolytic enzymes (collagenase and neutral proteases) and cysteine proteases, which presumably facilitate its tissue invasion. The parasite also elaborates a range of enzymes on the amebic surface, including membrane-associated neuraminidase and β-glucosaminidase (166, 223, 234)."
"E. histolytica contains proteolytic enzymes (collagenase and neutral proteases) and cysteine proteases, which presumably facilitate its tissue invasion. The parasite also elaborates a range of enzymes on the amebic surface, including membrane-associated neuraminidase and β-glucosaminidase (166, 223, 234)."


[[Image:PROTFIG40.jpg‎|thumb|300px|right|Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.]]


<br>At right is a sample image insertion.  It works for any image uploaded anywhere to MicrobeWiki.  The insertion code consists of:
<br>At right is a sample image insertion.  It works for any image uploaded anywhere to MicrobeWiki.  The insertion code consists of:

Revision as of 00:49, 6 December 2013

Introduction


Background Information

First identified by Hippocrates around 300 B.C. who described a patient with dysentery and fever, amoebiasis is a gastrointestinal infection due to the amoeba, Entamoeba histolytica. Later developments came in 1855 when it was suggested that the disease might have a parasitic origin. Finally,
E. histolytica was identified from a stool sample in 1875 by Fredor Losch. Throughout the world, amoebiasis is the second leading cause of death from a parasitic disease with an estimated 50 million cases per year and 100,000 deaths per year. However, most of these cases occur in the developing world. Although it is the second leading cause of death from parasitic diseases, about 90% of the people exposed to
E. histolytica are asymptomatic or report very mild symptoms. [Image:Ehistdisp_cyst_wtmt.jpg‎|thumb|300px|right|
E. histolytica cyst stained with iodine on a concentrated wet mount.]]


E. histolytica secretes proteinases that do considerable damage to its host. They can dissolve the tissues of the host by killing the host cells on contact; the cells become immobile and soon they will lose their cytoplasmic granules and structures. Finally, the nucleus of the cell will disintegrate. The proteinases can also engulf the red blood cells of the host. For those that do experience the symptoms associated with the Entamoeba histolytica infection, the onset is variable; they can occur gradually or very quickly. Gradual symptoms most often include a slow onset of colitis, or inflammation of the colon. Associated with colitis is diarrhoea and abdominal pain. Diarrhoea usually begins mildly and develops into diarrhoea that contains blood and mucous. Other signs of colitis are nausea, headache, and sometimes fever in less than forty percent of individuals. On the other hand, symptoms that occur quickly and intensely include semi liquid stools that contain blood and mucous. Abdominal pain can range from mild to severe, frequently accompanied by a tender liver. Rarer progressions of the disease include brain abscesses.


Prognosis

Mortality rates from the infection also varies widely depending on what organs
E. histolytica attacks. If the individual develops fulminant amoebic colitis, they have an associated mortality rate of between 55% to 87.5%. If amoebic liver-abscess occurs, which is also the most common path the disease takes outside of the intestines, mortality rates are generally from 1-3%. Death comes quickly to about half of individuals who develop amoebic brain abscesses.


Transmission

Entamoeba histolytica can be transmitted a number of ways, but most commonly is it transferred from fecal matter, where
E. histolytica cysts are present, to oral ingestion. It is also transmitted from contaminated food or water sources, which are common in places such as Mexico, Central America, and South Asia. Some researchers have suggested a zoonosis pathway may also exist, but further studies still need to be conducted to prove this.


Entamoeba histolytica Structure and Lifecycle

While existing in the cyst stage of its life cycle,
E. histolytica tend to have a diameter of 10–15μm and are round in shape. Within a refractile wall containing chitin, are four nuclei, glycogen, and chromatoid bodies (ribosomal assemblies). As a trophozoite,
E. histolytica are generally larger, of around 10 to 50μm in diameter. Unlike in the cyst form, the trophozoites are capable of moving spontaneously, gaining the energy for this process through anaerobically converting glucose and pyruvate to ethanol. Trophozoites can reproduce by binary fission

Once ingested by a human or a non-human primate, who are the natural hosts to the parasite, the
E. histolytica cysts travel to the small intestine and become trophozoites in either the terminal ileum or colon (each cyst will produce eight trophozoites). Cysts can exist outside the human body for long periods of time (from days or even up to months in damp conditions and ideal temperatures), Unlike cysts, trophozoites cannot survive outside of this preferred environment, and will degrade very quickly if exposed to an outside environment. The incubation period of the amoeba can vary from a couple of days to as long as a year. Nonetheless, once in the small intestine, the trophozoites will attack the intestinal epithelial cells of the gastrointestinal tract. Not only do they invade the gastrointestinal track, but trophozoites can also migrate to other organs of the body and cause infection there as well. Once in the colon of its host, the trophozoites will encyst again and exit the body through the stool


E. histolytica trophozoite measured at 40 micrometers in length from a patient with moderate diarrhea


Treatment

The first successful treatment came about in 1912. Leonard Rogers used emetine. Today, those identified as infected by
E. histolytica are treated with two types of drugs. The first is an amoebicidal agent as well as a luminal-acting cysticidal agent. Physicians will usually use a CT to monitor the abdomen of an infected individual and use a catheter to drain fluid. For people with the identified infection, but who do not show symptoms, should still be put on a luminal agent as they pose a health risk to others. Furthermore, 4-10% of asymptomatic people will develop symptoms within a year of the infection.

"E. histolytica contains proteolytic enzymes (collagenase and neutral proteases) and cysteine proteases, which presumably facilitate its tissue invasion. The parasite also elaborates a range of enzymes on the amebic surface, including membrane-associated neuraminidase and β-glucosaminidase (166, 223, 234)."



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Legend/credit: Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.
Closed double brackets: ]]

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Section 1

Development of Diagnoses Methods It is important to have as precise methods as possible in detecting
E. histolytica in order to determine the extent of the amoebiasis infection. Furthermore, the more that is understood about
E. histolytica, researchers are better to develop treatments. The methods that are most commonly used to detect the presence of the parasite are ELISA(enzyme-linked immunosorbent assay) or IHA(indirect hemagglutination assay).


E. histolytica has usually been detected by looking at morphology, but in recent years there have been many advancements in detection. It is difficult though, to detect morphological differences in protozoa because many of them look very similar. Furthermore, it hard to distinguish between
E. histolytica and E. dispar using old methods as well. The only way one could distinguish between the two was if erythrophagocytosis, or the ingested RBCs in the trophozites of E. histolytica, was seen under a microscope. And even this method is not always conclusive as other amebic infections have RBCs, although they are not observed as frequently. Thus, it is important that new diagnosis techniques are being developed.

Now, serological testing is more a useful and definitive way of testing for
E. histolytica. This, coupled with antigen detection and PCR, may offer the best way to diagnose patients. ELISA (enzyme-linked immunosorbent assay) are becoming increasingly popular in diagnoses because symptomatic patients are thought to have high levels of specific antibodies, serum anti-lectin immunoglobulin G (IgG), associated with the E histolytica infection. These antibodies can be detected within one week of the start of the symptoms.

Microscopy/Biochemical Methods Microscopy has historically been the most prominent method of detecting
E. histolytica. However, researchers are now discovering that it is difficult to to detect morphological differences among similar protozoa. There is another emerging problem becoming apparent with diagnosing amoebiasis with microscopy: ELISA

Section 2

Genomic Diversity of Amoebiasis Research on the genome of
E. histolytica is an emerging area of importance in understanding the virulence of the parasite. In fact, recent studies have proposed that it's genetic factors affect how infectious it is. The genomes of several strains of E. histolytica have been sequenced, which yielded interesting data about the amoeba. For example, it was discovered that about 75% of the genome consists of A and T nucleotides. Furthermore, among the strains sequenced nucleotide differences were low (single-nucleotide polymorphism ranged from 0.312 to 0.857 SNPs per kilobase). Conversely, other studies have found high diversity in the nucleotide repeats that separate tRNA genes or genes like that coding for SREHP, a protein consisting of a large amount of serine. However, gene copy number is diverse, suggesting that this could be an important part of the variety of virulence seen from the parasite.

Recent research provides evidence that
E. histolytica reproduces sexually, a phenomena that has not yet been observed in the genus, Entamoeba. It was discovered that the particular strain of
E. histolytica, HM-1:IMSS, contains most of the genes that contribute to meiosis. Thus, sexual reproduction probably provides a significant amount of the diversity observed in the genomes of the strains through events such as recombination and reassortment of alleles.

Conclusion

Overall text length should be at least 1,000 words (before counting references), with at least 2 images. Include at least 5 references under Reference section.

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.


Edited by Kelsey Hauser, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2013, Kenyon College.