Parasites In Humans
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Entamoeba Histolytica - Amoebiasis

Entamoeba histolytica is a protozoan parasite responsible for a disease called amoebiasis. It occurs usually in the large intestine and causes internal inflammation as its name suggests (histo = tissue, lytic = destroying). 50 million people are infected worldwide, mostly in tropical countries in areas of poor sanitation. In industrialized countries most of the infected patients are immigrants, institutionalized people and those who have recently visited developing countries.

Inside humans Entamoeba histolytica lives and multiplies as a trophozoite. Trophozoites are oblong and about 15–20 µm in length. In order to infect other humans they encyst and exit the body. The life cycle of Entamoeba histolytica does not require any intermediate host. Mature cysts (spherical, 12–15 µm in diameter) are passed in the feces of an infected human. Another human can get infected by ingesting them in fecally contaminated water, food or hands. If the cysts survive the acidic stomach, they transform back into trophozoites in the small intestine. Trophozoites migrate to the large intestine where they live and multiply by binary fission. Both cysts and trophozoites are sometimes present in the feces. Cysts are usually found in firm stool, whereas trophozoites are found in loose stool. Only cysts can survive longer periods (up to many weeks outside the host) and infect other humans. If trophozoites are ingested, they are killed by the gastric acid of the stomach. Occasionally trophozoites might be transmitted during sexual intercourse.

Entamoeba histolytica life cycle

Most Entamoeba histolytica infections are asymptomatic and trophozoites remain in the intestinal lumen feeding on surrounding nutrients. About 10–20 % of the infections develop into amoebiasis which causes 70 000 deaths each year. Minor infections (luminal amoebiasis) can cause symptoms that include:

  • gas (flatulence)
  • intermittent constipation
  • loose stools
  • stomach ache
  • stomach cramping.

Severe infections inflame the mucosa of the large intestine causing amoebic dysentery. The parasites can also penetrate the intestinal wall and travel to organs such as the liver via bloodstream causing extraintestinal amoebiasis. Symptoms of these more severe infections include:

  • anemia
  • appendicitis (inflammation of the appendix)
  • bloody diarrhea
  • fatigue
  • fever
  • gas (flatulence)
  • genital and skin lesions
  • intermittent constipation
  • liver abscesses (can lead to death, if not treated)
  • malnutrition
  • painful defecation (passage of the stool)
  • peritonitis (inflammation of the peritoneum which is the thin membrane that lines the abdominal wall)
  • pleuropulmonary abscesses
  • stomach ache
  • stomach cramping
  • toxic megacolon (dilated colon)
  • weight loss.

To prevent spreading the infection to others, one should take care of personal hygiene. Always wash your hands with soap and water after using the toilet and before eating or preparing food. Amoebiasis is common in developing countries. Some good practices, when visiting areas of poor sanitation:

  • Wash your hands often.
  • Avoid eating raw food.
  • Avoid eating raw vegetables or fruit that you did not wash and peel yourself.
  • Avoid consuming milk or other dairy products that have not been pasteurized.
  • Drink only bottled or boiled water or carbonated (bubbly) drinks in cans or bottles.

Natural water can be made safe by filtering it through an "absolute 1 micron or less" filter and dissolving iodine tablets in the filtered water. "Absolute 1 micron" filters are found in outdoor/camping supply stores. Micron = micrometer = 0.001 mm.

Amoebiasis is diagnosed by your health care provider under a microscope by finding cysts and (rarely trophozoites) from a stool sample. The results are usually said to be negative, if Entamoeba histolytica is not found in three different stool samples. But it still does not necessarily mean that you are not infected because the microscopic parasite is hard to find and it might not be present the particular samples. A blood test might also be available but is only recommended, if your health care provider believes that the infection could have spread to other parts of the body. Trophozoites can be identified under a microscope from biopsy samples taken during colonoscopy or surgery.

Entamoeba histolytica should be differentiated from the non-pathogenic Entamoeba dispar. The two are morphologically identical and differentiation must be based on immunologic or isoenzymatic analysis or molecular methods. They can be distinguished under a microscope, if Entamoeba histolytica has ingested red blood cells. Entamoeba dispar is about 10 times more common. If either one is found, then you are usually treated.

If you are experiencing amoebiasis symptoms, you are treated with two antibiotics. The preferred drugs are metronidazole or tinidazole immediately followed with paromomycin, diloxanide furoate or iodoquinol. Asymptomatic intestinal amoebiasis is treated with paromomycin, diloxanide furoate or iodoquinol.

cysttrophozoites which have ingested red blood cellsentamoeba histolytica trophozoite 

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