Entamoeba Dispar - A Non-pathogenic Protozoan

Introduction:

Entamoeba dispar is a non-pathogenic protozoan, but some experimental studies showed that Entamoeba dispar could be pathogenic too. Entamoeba histolytica and Entamoeba dispar are two morphologically identical species, and the two can be differentiated only by laboratory diagnosis. In humans, Entamoeba dispar colonizes the colon of the large intestine. According to World Health Organization (WHO), approximately 50 million cases and 100000 deaths annually are reported due to Entamoeba histolytica, and Entamoeba dispar is the more prevalent species. Entamoeba dispar was discovered by Brumpt in 1925 and later recognized by Diamond and Clark in 1993. The protozoa affect approximately 12 percent of the world's population. Entamoeba dispar has a worldwide distribution, but the parasite is highly prevalent in developing countries. Entamoeba dispar is more common in people living in endemic areas, including Mexico, India, Africa, Central America, and South America. Entamoeba dispar consists of two life forms that are the trophozoite and cyst.

What Does Entamoeba Dispar Cause?

• Entamoeba dispar is the most prevalent species. It is associated with an asymptomatic carrier state (the species are present in humans but not causing any symptoms).

• Entamoeba dispar has been identified in homosexual men.

• Entamoeba dispar causes a liver abscess (pus-filled within the liver), colitis (colon inflammation), and extraintestinal infection.

What Is the Morphology of Entamoeba Dispar?

The morphology consists of three stages: the trophozoite, precyst, and cyst. They are as follows.

1. Trophozoite -

• The trophozoites are the growing and feeding stage of parasites.

• The shape is not fixed because of the constant changing of the position.

• The size ranges from 18 to 40 um (micrometer), and the average range is 20 to 30 um.

• The cytoplasm is divided into two portions one is clear ectoplasm, and another is granular endoplasm. In endoplasm, granules and vacuoles contain food material and debris. Red blood cells are present.

• The single nuclei are spherical in shape and size, ranging from 4 to 6 um. The nucleus contains the central karyosome (central portion of cell nucleus) and fine peripheral chromatin.

• They have pseudopodia (an arm-like projection raised from the cell membrane) for locomotion and are motile.

2. Pre-cyst -

• It is the intermediate stage between the cyst and trophozoite and is smaller in size ranging from 10 to 20 um.

• The pre-cyst is round to oval with blunt pseudopodium.

3. Cyst -

• The cyst is the parasite's infective stage.

• The shape is round to oval, ranging from 12 to 15 in diameter.

• The cyst is surrounded by a membrane called a cyst wall.

• The mature cyst consists of a quadrinucleated cyst.

• Cytoplasm shows chromatid bars and glycogen mass, but the red blood cells and food debris are absent.

• The mature cyst passes in the stool and remains in the soil for a few days.

What Is the Mode of Transmission of Entamoeba Dispar?

The life cycle consists of the infective cyst stage and the trophozoite stage. Humans are the host of the parasite. Humans get infected with Entamoeba dispar from contaminated food and water. The protozoa are transmitted through the fecal-oral route. The parasite lives in the colon of the large intestine. The life cycle is described as follows.

• Both the trophozoites and cysts are passed in the stool. The cyst is found in the healthy stool, and the trophozoites are in the diarrheal stool.

• The non -pathogenic protozoa colonize after the ingestion of the cysts in food and water contaminated with feces.

• Excystation (removal of cyst) occurs in the small intestine, releasing the trophozoites into the large intestine. The trophozoites multiply by binary fission and produce cysts.

• Both trophozoites and cysts pass through the feces. The cyst can survive in the external environment because of the protection provided by the cell wall. The cyst is responsible for the transmission of infection.

• The trophozoites in the stool are destroyed in the external environment.

What Are the Risk Factors of Entamoeba Dispar?

Entamoeba dispar can occur in any age, race, and sex. The risk factor includes.

• Source of drinking water (people drink water from the deep wells contaminated with feces).

• Consumption of unwashed vegetables and fruits.

• Poor personal hygiene.

• Low socioeconomic status.

• Exposure to human and animal excreta in agricultural activities.

What Are the Signs and Symptoms of Entamoeba Dispar?

Entamoeba dispar is a non-pathogenic amoeba, so it often shows no symptoms. If the parasite shows symptoms, it includes.

• Fever.

• Abdominal pain.

• Diarrhea.

• Nausea.

• Vomiting.

• Colitis.

• Liver abscess.

• Extraintestinal infections (outside the intestine causing urinary tract infection).

How Is Entamoeba Dispar Infection Diagnosed?

Entamoeba dispar can be diagnosed by following investigation includes.

1. Wet Mount - In bright field microscopy, the cysts are spherical and measure 12 to 15 um. The mature cyst contains four nuclei, and the immature cyst contains one to three nuclei. Glycogen can be diffuse or absent in mature cysts.

2. Trichrome Stain - The trophozoites in trichrome smear measures 15 to 20 um. It is present with only one nucleus. The cytoplasm is granular and ingests a few bacteria and debris. Ingested red blood cells are not seen.

3. Enzyme Immune Assays - The test is used to identify cysts and trophozoites. The test requires fresh or frozen stool samples and cannot be used with preserved samples.

4. Rapid Immunochromatographic Cartridge Assay - A rapid cartridge is used to detect the antigen of Entamoeba dispar. The stool samples must be frozen or fresh. The test is easy and quick to perform. It does not require any special equipment.

Wet mount preparation and trichrome stained smears of stool samples are the common procedures to identify Entamoeba dispar.

How Is Entamoeba Dispar Infection Managed?

Entamoeba dispar is seen in stool samples, so the patient should be treated with anti-parasitic drugs. The doctor may prescribe Metronidazole and Diloxanide furoate to treat severe colitis and to prevent future invasion with the remaining cyst.

• The dose of Metronidazole is 750 mg thrice daily for ten days, followed by luminal agent Diloxanide furoate 500 mg three times daily or Paromomycin 500 mg three times daily.

How Can Entamoeba Dispar Infection Be Prevented?

The preventive measures are as follows.

• Proper personal hygiene.

• Avoidance of contaminated food and water.

• Proper disposal of sewage.

• Filtration of drinking water.

• Use of insecticides.

• Vegetables and fruits must be washed properly.

• Education to the people by medical staff about the infection.

Conclusion:

Entamoeba dispar is a non-pathogenic amoeba. The parasite may remain asymptomatic, but the carrier state may spread the infection to other community members. Healthcare professionals, including doctors, nurses, and pharmacists, can organize camps in rural areas to educate people about preventing and eliminating the infection. People can adopt preventive measures to eliminate the infection. Healthcare teams can work together to achieve better outcomes.