ENTAMOEBA HISTOLYTICA

 

INTRODUCTION:  Entamoeba histolytica is significant as the causative agent of the worldwide occurring entamebosis, a disease particularly prevalent in warmer countries. The vegetative stages also known as trophozoites of E. histolytica live in the large intestine and form encysted stages also known as cysts, that are excreted with feces.  The infection is transmitted by cysts from one human to another. The trophozoites of E. histolytica can penetrate into the intestinal wall and invade the liver and other organs hematogenously to produce clinical forms of amebosis, most frequently intestinal ameboses also termed “amebic dysentery” and hepatic amebosis frequently called “amebic liver abscess”.  Diagnosis of an intestinal infection is primarily confirmed by detection of the parasites in stool. If an invasive, intestinal or extraintestinal infection with E. histolytica is suspected, a serological antibody test can also provide valuable information.

OCCURRENCE AND PATHOGENICITY:  In endemic areas in Africa, Asia, and Central and South America up to 70–90% of the population can be are carriers of E. histolytica. The causative agent of amebosis is the pathogenic E. histolytica.  The trophozoites colonize the large intestine mucosa or lumen. E. histolytica can disseminate to other organs from the intestinal wall, most particularly to the liver. As a result of the destruction of parenchymal cells, small necrotic foci, so-called abscesses, form and gradually become larger and can even affect major portions of the organ.

EPIDEMIOLOGY:  Humans are the reservoirs for E. histolytica. The infection is due to transmission of mature cysts with contaminated foods especially from fruit, vegetables, drinking water or fecally contaminated hands. Flies and cockroaches can function as intermediaries by carrying cysts from the feces of an excretor to foods. The amounts of chlorine normally added to drinking water are insufficient to kill the cysts.

CLINICAL MANIFESTATIONS:  Clinical symptoms can develop as early as two to four weeks after infection with E. histolytica or after asymptomatic periods of months or even years. The acute disease usually begins with abdominal discomfort and episodes of diarrhea of varying duration, at first mushy then increasing mucoid, including blood-tinged, so-called “red currant jelly stools” in which amebas can be detected, including trophozoites containing erythrocytes. In such cases, antibodies are usually present in serum.

Extraintestinal forms:  Extraintestinal forms develop because of hematogenous dissemination of E. histolytica originating in the intestine. The most frequent form is the so-called “liver abscess,” which may develop in some infected persons. Only about 10% of patients with liver abscesses are also suffering from amebic colitis.  

The liver abscess causes remittent fever, upper abdominal pain, liver enlargement, elevation of the diaphragm, general weakness, and other symptoms.  Antibodies are detectable in most cases

THERAPY:  Nitromidazole derivatives are effective against symptomatic intestinal and extraintestinal forms of amebosis. On the other hand, amebicides with only luminal activity are effective against asymptomatic intestinal amebosis.

PREVENTION:  Travelers to endemic areas should decontaminate drinking water by boiling or filtering it, not eat salads, eat only fruit they have peeled themselves and exercise caution when it comes to changing their diet. Chemoprophylactic dugs are not available.

 

RELATED;

1.  PLASMODIUM

2.  BACTERIOLOGY

3.  VIROLOGY

4.  ANTIMICROBIAL AGENTS

5.  PROTOZOA

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