Entamoeba Histolytica Infection - Caused by Amebic Dysentery

Entamoeba Histolytica Infection - Caused by Amebic Dysentery
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Entamoeba histolytica are parasites or commensals of humans and domestic animals. They are transferred via fecal-oral route.

Entamoeba histolytica was once used as a biological weapon in different wars such as the World War II and Vietnam War. It was proven more effective in inflicting more casualties than bombs and bullets. This microorganism is the caused of amebic dysentery which is fatal if not given proper medical attention. It is estimated that approximately 500 million people are infected at any one time and up to 100,000 deaths occur annually (Meyer 1992). High incidence of amebiasis is prevalent in areas of poor sanitation_._

Entamoeba histolytica Pathogenesis

Entamoeba histolytica is distinctive among amebas of humans in its ability to hydrolyze host tissues. It has active cysteine proteases on its surfaces which are capable of hydrolyzing intestinal cells. An intestinal lesion usually develops initially in the cecum, appendix, or upper colon and then spreads the length of the colon. Parasite numbers build up in the ulcer, increasing the speed of mucosal destruction. The muscularis mucosa is somewhat of a barrier to further progress, and pockets of amebas form, communicating with the intestinal lumen through a slender, duct like opening. The lesion may stop at the basement membrane or at the muscularis mucosae and then begin eroding laterally, causing broad, shallow areas of necrosis. Bacteria then begin to infect the lesions and will help the ameba to break through the muscularis mucosae, infiltrate the submucosa, and even penetrate the muscle layers and serosa. This enables the ameba to be carried by blood and lymph to different organs of the body where secondary lesions then form. A high percentage of deaths results from perforated colons with concomitant peritonitis. Surgical repair of perforation is difficult because heavily ulcerated colon becomes very delicate.

Secondary lesions have been found in nearly every organ of the body but the liver is most commonly affected. Regardless of the secondary site, the initial infection is an intestinal blister, even though it may go undetected. Hepatic amebiasis results when amebas enter mesenteric venules and travel to the liver through the hepatoportal system. They digest their way through portal capillaries and enter the sinusoids, where they begin to form abscesses.

Pulmonary amebiasis is the next most common secondary lesion. It usually develops by metastasis from a hepatic lesion but may originate independently. Most cases originate when a liver abscess ruptures through the diaphragm. Others sites that can be infected are the skin, brain, spleen, kidneys, penis, pericardium and others.

Symptoms of Entamoeba histolytica Infection

Most commonly, the disease develops slowly, with intermittent diarrhea, cramps, vomiting, and general malaise. Infection in the cecal area may mimic symptoms of appendicitis. Some patients tolerate intestinal amebiasis for years with no sign of colitis (although they are passing cysts) and then suddenly succumb to ectopic lesions. Depending on the number and distribution of intestinal lesions, a patient might experience pain in the entire abdomen, fulminating diarrhea, dehydration, and loss of blood. Amebic diarrhea is marked by bouts of abdominal discomfort with four to six loose stools per day but little fever.

Acute amebic dysentery is a less common condition, but sufferers of this affliction can best be described as miserable. The onset may be sudden after an incubation period of 8 to 10 days or after a long period in which the sufferer has been an asymptomatic cyst passer. In acute onset there may be headache, fever, severe abdominal cramps, and sometimes prolonged, ineffective straining at stool. An average of 15 to 20 stools, consisting of liquid feces flecked with bloody mucus, is passed per day. Death may occur from peritonitis, resulting from gut perforation, or from cardiac failure and exhaustion.

Diagnosis of Entamoeba histolytica Infection

Examination of stool samples is the most effective means of diagnosis of gut infection. A direct smear examined either as wet mount or fixed and stained will usually reveal heavy infections. X-ray examination and other means of scanning the liver may be useful in detecting abscesses, and ELISA assays for amebic lectin antigens, including those in saliva, have been developed for use in diagnosis.

Treatment of Entamoeba histolytica Infection

Several drugs have a high level of efficacy for the treatment of amebiasis. Most fall into the categories of arsanilic acid derivatives, iodochlorhydroxyquinolines, and other synthetic and natural chemicals. Antibiotics, particularly tetracycline, are useful as bactericidal adjuvant. Metronidazole has become the preferred drug in treatment of amebiasis. It is low in toxicity and is effective against both extraintestinal and colonic infections, as well as cysts.

Entamoeba histolytica Infection Reference

Meyer, Marvin. 1992. Essentials of Parasitology. Dubuque, Iowa: Wm.C. Brown.

Photo of E. histolytica cyst from https://en.wikipedia.org/wiki/File:Entamoeba_histolytica_01.jpg