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Entamoeba histolytica

Updated on December 26, 2014

What is Entamoeba histolytica?

Entamoeba histolytica (E. histolytica) is the only pathogenic species in the Entamoeba family which can cause invasive intestinal and extraintestinal diseases such as colitis and liver abscess.

Entamoeba histolytica under the microscope.
Entamoeba histolytica under the microscope. | Source

Life Cycle

  • There are two stages that E. histolytica undergoes to:
  1. Cyst - the infective stage. It is resistant to environmental stress such as gastric acidity and temperature changes.
  2. Trophozoite - the active stage. It is the stage that causes the pathogenicity of the disease.

The parasite enters the body through the ingestion of its cyst. In the intestines, the cyst will undergo excystation, where the cyst will experience nuclear and cytoplasmic division forming trophozoites. These trophozoites are responsible for the pathogenicity of the disease to take place. Before they are excreted in formed-feces, trophozoite will encyst, forming a cyst that will further undergo maturation. Once the feces exit the body, the cyst is ready to be ingested by another living host.

*If the stool is watery, encystation is not necessary. Trophozoites are present rather than cysts.

The life cycle of E. histolytica
The life cycle of E. histolytica | Source

Pathogenesis and Clinical Manifestations

Amoebiasis is the infection caused by E. histolytica. There are two types of amoebiasis:

  1. Intestinal Amoebiasis - infection in the intestines
  2. Extraintestinal Amoebiasis - infection outside the intestines

Intestinal Amoebiasis is the most common type of amoebiasis, occurring almost 90% of all the cases of amoebiasis. Amoebic colitis results in abdominal pain and diarrhea alternating with constipation. Some patients may develop bloody diarrhea and fever. Amoeboma is a mass-like lesion formed in the intestinal wall resulting into the thickening wall and constriction of the intestinal lumen. This granuloma may resemble colon cancer, which can lead to misdiagnosis.

Extraintestinal Amoebiasis may occur in the liver (hepatic amoebiasis), lungs (pulmonary amoebiasis), brain (cerebral amoebiasis) and skin (cutaneous amoebiasis).

Laboratory Diagnosis

Diagnosis is often done by the presence of E. histolytica cyst in the stool through microscopic examination. However, the parasite resembles another Entamoeba parasite, Entamoeba dispar, which can lead to misdiagnosis, then wrong prescription of drugs. It is important to take note of the only characteristic of E. histolytica that can be used to differentiate it from E. dispar. Presence of red blood cells inside the cyst is a positive demonstration of amoebiasis.

Serological tests are also available which detects antibodies in the blood against E. histolytica.

Preventive Measures

The transmission of amoebiasis can be prevented by practicing proper sanitation. Proper food preparation, clean sewage and waste disposal system can also help the increasing number of the said infection.

Source

Treatment

Amoebicides is the collective term used for drugs against E. histolytica.

Summary

Entamoeba histolytica is a parasite that can cause amoebiasis, an infection resulting to mainly intestinal problems in the human host. The infection can spread through the ingestion of contaminated food and water. Diagnosis can be based from the presence of the parasite's cysts in the patient's stool. Proper sanitation can help prevent the spread of the infection.


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