Amoebiasis natural history, complications and prognosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Following transmission, individuals typically remain asymptomatic for approximately 1 to 4 weeks (up to several years), during which the parasite starts to actively destroy to integrity of the intestinal wall.
The majority of colonized patients do not develop any clinical manifestations.
The infection rate of E. histolytica is approximately 10%-20%, whereas the infection rate of E. dispar is approximately 0% (since E. dispar is not associated with invasive disease).

As the parasite continues to invade the intestinal wall, the integrity of the wall is compromised, and the host immune cells are activated. The activation of neutrophils, macrophages, lymphocytes, and eosinophils contribute to the inflammation and the development of clinical manifestations.
The development of symptoms occurs gradually over 1-2 weeks. Early symptoms include profuse, watery diarrhea, abdominal pain, bloating, and nausea.
If left untreated, the majority of patients report self-resolution of symptoms.
In a minority of cases, however, the disease may progress and patients develop bloody diarrhea (dysentery), fulminant colitis, appendicitis, toxic megacolon, and ameboma (granulation tissue in the colon).

As the infection advances, the parasite is able to migrate outside the intestinal lumen into the bloodstream, where it is able to migrate to distant organs.
If left untreated, the most site of parasitic migration is the liver, whereby the parasite travels in the portal circulation and causes amoebic liver abscess.
Other organs may also be affected, including the brain (cerebral amoebiasis), pulmonary system (pleuropulmonary abscess), skin, and genitals.

Patients with untreated amoebiasis may develop chronic disease.
The symptoms of chronic amoebiasis resemble inflammatory bowel disease (IBD).
The distinction between chronic amoebiasis vs. IBD is important since corticosteroid therapy is effective for IBD but worsens amoebiasis.

Complications of amoebiasis may be either intestinal or extraintestinal: