Entamoeba histolytica Laboratory Diagnosis

Laboratory Diagnostic of Entamoeba histolytica

Entamoeba histolytica infection occurs in as many as 10 percent  of the world’s population and is considered a leading cause of parasitic deaths after malaria, the clinical manifestation of infection with plasmodium species parasites and schistosomiasis, the umbrella term for the disease associated with schistosoma spp Infection.This parasite thrives not only in subtropical and tropical regions of the world, but also in colder climates such as Alaska, Russia and Canada.In places where human waste is used as fertilizer, poor sanitation areas, hospitals for the mentally ill, prisons and day nurseries, Entamoeba histolytica is usually housed.This organism has been prevalent in homosexual communities in the past as it causes frequent asymptomatic infections in homosexual men, especially in Western countries.There are several known means of transmitting Entamoeba histolytica.The ingestion of the infection stage, the cyst, occurs through mouth to mouth contamination and through contamination of food or water.In addition, Entamoeba histolytica can also be transmitted via unprotected sexual intercourse.Flies and cockroaches may also serve as vectors (living carriers responsible for the transmission of parasites from infected hosts not infected hosts) of Entamoeba histolytica by depositing infectious cysts on unprotected food.Improperly treated water supplies are additional sources of infection.

Morphology of Entamoeba histolytica


The trophozoites of Entamoeba histolytica range in size from 8 to 65 µm, with an average size of 12 to 25 µm.Trophozoite shows rapid, unidirectional, progressive motion, achieved by finger-like hyaline pseudopods.The single nucleus normally contains a small central mass of chromatin known as karyosome (also called karyosomal chromatin).Variants of karyosome closure Eccentric or fragmented karyosomes material.The karyosome of these amoebae parasite is surrounded by chromatin material, a morphological structure known as peripheral chromatin, which is typically in order and uniform around the nucleus in a perfectly distributed circle.Variations such as uneven peripheral chromatin can also be seen.Although the karyosome and peripheral chromatin may vary, most trophozoites obtain described multi typical characteristics.The invisible nucleus in unstained preparations becomes apparent when stained.Stained specimens may show slightly discoloured fibrils between the karyosome and peripheral chromatin.The Entamoeba histolytica trophozoite contains a finely granular

cytoplasm, which is often referred to as having a ground glass in appearance.red blood cells (RBCs) in the cytoplasm are considered to be diagnostic, Entamoeba histolytica is the only intestinal amoeba having this characteristic.Bacteria,yeast, and other debris may also reside in the cytoplasm, but their presence, however, is not diagnostic.

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Entamoeba histolytica trophozoites
Entamoeba histolytica trophozoites


The spherical to round cysts of Entamoeba histolytica are usually smaller than the trophozoites and measure 8 to 22 µm with an average range of 12 to 18 µm.The presence of a hyaline cyst wall helps to recognize this morphological form. Young cysts characteristically contain unorganized chromatin material that converts into square or rounded structures known as chromatids, known as structures containing condensed RNA material.A diffuse glycogen mass, a cytoplasmic region without defined boundaries that is thought to represent stored food, is normally also visible in young cysts.As the cyst matures, the glycogen mass usually disappears, a process that probably represents the use of stored food.Usually one to four nuclei are present.

These nuclei seem to be the same as those of the trophozoite in every respect, but are usually smaller.Nuclear variations occur, the most common of which are eccentric (instead of the typical central) karyosomes, thin plaques of peripheral chromatin or a tuft of peripheral chromatin on one side of the nucleus that appears crescent.The nuclei are enlarged to show the nuclear detail.The mature infectious cyst has four nuclei (contains four nuclei).The cytoplasm remains fine and granular.Erythrocytes, bacteria, yeasts and other residues are not found at the cyst stage.

Entamoeba histolytica cyst
Entamoeba histolytica cyst

Life Cycle of Entamoeba histolytica

Once the infective cyst is ingested, excystation occurs in the small intestine.As a result of thenuclear division, a single cyst produces eight motile trophozoites.These motile amoebae settle in the lumen of the colon, where they replicate by binary fission and feed on living host cells.Occasionally trophozoites migrate to other organs of the body, such as the liver, and can cause the formation of abscesses.If these trophozoites do not return to the lumen of the colon, their life cycle stops and the diagnosis in such cases depends on serological tests.The encystation takes place in the intestinal lumen and cyst formation is completed when four nuclei are present.These infectious cysts are released into the environment with human faeces and are resistant to a variety of physical conditions.survival in a excrement-loaded environment for up to 1 month is usual.It is important to know that besides cysts, trophozoites may also be present in the stool under the right conditions. Liquid or semi-formed samples may show trophozoites at fast intestinal motility. Cysts, on the other hand, form when the bowel motility is normal.

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Entamoeba histolytica life cycle
Entamoeba histolytica life cycle

Clinical symptoms of amoebiasis

Entamoeba histolytica is the only known pathogenic intestinal amoeba. The range of symptoms varies and depends on two major factors:

  • location(s) of the parasite in the host
  • the extent of tissue invasion.

Asymptomatic Carrier State

Three factors, acting separately or in combination, are responsible for the asymptomatic carrier state of a patient infected with Entamoeba histolytica:

  • the parasite is a low-virulence strain
  • the inoculation into the host is low
  • the patient’s immune system is intact.

Symptomatic Intestinal Amebiasis

Patients infected with Entamoeba histolytica and showing symptoms often suffer from amoeba colitis, referred to as intestinal infection, caused by Amebas showing symptoms.In some cases, these patients can go from amoebic colitis to a condition called amoebic dysentery due to blood and mucus in the stool.Individuals with amoebic colitis may experience indeterminate abdominal symptoms or may complain of more specific symptoms, including diarrhea, abdominal pain and cramps, chronic weight loss, anorexia, chronic fatigue and flatulence.

Secondary bacterial infections can develop in the large intestine, appendix, appendix or rectosigmoid region of the intestine after the formation of flask-shaped amoebic ulcers.As already mentioned, bowel movements recovered from patients with amoebic dysentery are characterized by the presence of blood and/or pus and mucus.

Symptomatic Extraintestinal Amebiasis

Entamoeba histolytica Trophozoites that migrate into the bloodstream are removed from the liver and reside there.The formation of an abscess in the right lobe of the liver and the enlargement of the trophozoite through the diaphragm can lead to amoebic pneumonitis.Patients in this condition often show symptoms similar to those of a liver infection and cough, with the most common symptoms in the right upper abdomen being pain with fever.weakness, weight loss, sweating, severe nausea and vomiting and constipation with or without diarrhea may occur.

In addition to the liver, Entamoeba histolytica is known to migrate to and infect other organs such as the lungs, pericardium, spleen, skin and brain.There may also be amebiasis.Men become infected with penile amebiasis after having unprotected sex with a woman who has vaginal amebiasis.The disease can also be transmitted during anal intercourse.It is interesting to note that the trophozoite form of Entamoeba histolytica occurs most frequently in the examination of these genital areas.

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Treatment of Amebiasis

Treatment regimens for patients infected with Entamoeba histolytica vary depending on the type of infection.Since it is feared that an infection with Entamoeba histolytica can only become symptomatic in the intestine or with subsequent extraintestinal invasion, asymptomatic persons can be treated with paromomycin, diloxanide furoate (furamide) or metronidazole (flagyl).

Patients with symptomatic intestinal amebiasis typically respond well to iodoquinol, paromomycin or diloxanide furoate.Metronidazole or tinidazole in combination with symptomatic treatment with intestinal tract amebiasis is recommended for patients who have advanced to extraintestinal amebiasis.

Prevention and Control of Amebiasis

Several steps can be taken to prevent infection with Entamoeba histolytica.Non-contaminated water is essential and this can be achieved by cooking or treating with iodine crystals.It is interesting to note that the infective(four nuclei) cyst is resistant to routine chlorination.In order to ensure a safe water supply, a water treatment scheme including filtration and chemical treatment is required.Proper washing of food, avoidance of faeces as fertilizers, good hygiene and hygiene practices, protection of food from flies and cockroaches, and avoidance of unprotected sexual practices serve to break the transmission cycle.

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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