CONTENTS

AMOEBIASIS

• Amoebiasis-Pathology
• Amoebiasis- the species
• Amoebiasis,Amoebic dysentery/ Entamoeba histolytic...

Amoebiasis-Pathology

Infectious disease caused by the amoeba Entamoeba histolytica which may be commensal in the gut for long periods of time, or it may invade The mucosa soon after infection. The dose of infection, the strain of amoebae, the nutritional State of the patient and the nature of the intestinal flora are likely to be determinants of the development of disease. Axenic animals with an intestine free of bacteria do not appear to develop invasive amoebic infection. Some strains of amoebae are more pathogenic and appear to share isoenzyme or genomic patterns, described as zymodemes or schizodemes. Although multiple pathogenic mechanisms of E. histolytica have been described,none have been definitively linked with pathogenicity.The amoebic trophozoites are best demonstrated with the periodic acid Schiff (PAS) technique because most trophozoites contain glycogen. Also, their cytoplasm stains more distinctly with Giemsa or eosin than the smaller macrophages. They adhere to the intestinal epithelium and generally invade in areas where the intestinal mucus appears depleted. The amoebae fan out in the lamina propria and submucosa, giving rise to ``flask-shaped'' ulcers.The histiolytic nature of the amoebae is suggested by the lysis of the surrounding cells, seen light microscopically by lysis of the nuclei and by ultra structural changes in the cytoplasm. However, the clear space around individual amoebae is largely a fixation artifact. Neutrophils are attracted by the amoebae and are degranulated and lysed.This release of neutrophil granules may contribute to tissue destruction. The absence of neutrophils around the ulcers is notable. The absence of fecal leukocytes with positive results of a guaiac test for blood is a useful diagnostic finding. However,eosinophilic leukocytes are often seen histologically and may be found in the stool. The magna-stages phagocytose red blood cells and cell debris which distinguishes E.histolytica from nonpathogenic amoebae. Intestinal ulcers may extend through the muscularis. And lead to intestinal perforations. This complication is made more likely by the administration of anti-inflammatory corticosteroids which can occur if an erroneous diagnosis of inflammatory bowel disease has been made. However AIDS patients do not appear to be especially susceptible to recrudescenses. The amoebae often invade the veins in the submucosa of the gut and are transported to the liver and rarely other organs (lung, brain, skin), where they may set up foci of infection. Liver abscesses may reach a size of several centimeters. They usually develop in the right Side according to the laminar flow of the portal vein drainage from the colon. The amoebae colonize lyse,and digest the liver cells, giving rise first to amoebic hepatitis .Only when the focus of destroyed liver parenchyma is too large for the lysed debris to be absorbed into the lymphatic and venous circulation will an abscess result. The center of the abscess is formed by brownish, semiliquid fluid which is said to resemble ``anchovy paste''. A liver abscess may extendthrough the diaphragm into pleura and lung with the abscess material being coughed up.
Older abscesses are surrounded by fibrinous chronic inflammatory reaction products or by fibrosis. The amoebic trophozoites are found in the periphery of the abscess between the liver cells, best identified in PAS-stained sections . The delicate nuclei of the trophozoites are shown with hematoxylin and eosin, but they stainless intensely than the nuclei of macrophages from which they need to be distinguished. Amoebic cysts are found only in the stools and not in the tissues. Invasive amoebiasis is enhanced by immunosuppressionof whatever cause, e.g., by corticosteroid administration, as mentioned above, and in patients with AIDS. E. histolytica infections also occur in extra intestinal sites, penile infections following anal intercourse, infections of the cervix uteri and the buccal mucosa.

Amoebiasis- the species

Amoebiasis,Amoebic dysentery/ Entamoeba histolytica infection.

Distribution


Distribution map of amoebic dysentery.