Most common site of abscess formation due to amoeba is: September 2005

Ans. B: Liver Amebic liver abscess is the most frequent extraintestinal manifestation of Entamoeba histolytica infection. This infection is caused by the protozoa E histolytica, which ascends the poal venous system. Amebic liver abscess is an impoant cause of space-occupying lesions of the liver, mainly in developing countries E histolytica exists in 2 forms. The cyst stage is the infective form, and the trophozoite stage causes invasive disease. People who chronically carry E histolytica shed cysts in their feces; these cysts are transmitted primarily by food and water contamination. Cysts are resistant to gastric acid, but the wall is broken down by trypsin in the small intestine. Trophozoites are released and colonize the cecum. To initiate symptomatic infection, E histolytica trophozoites present in the lumen must adhere to the underlying mucosa and penetrate the mucosal layer. Liver involvement occurs following invasion of E histolytica into mesenteric venules. Amebae then enter the poal circulation and travel to the liver where they typically form large abscesses. The abscess contains acellular proteinaceous debris, which is thought to be a consequence of induced apoptosis and is surrounded by a rim of amebic trophozoites invading the tissue. The right lobe of the liver is more commonly affected than the left lobe. This has been attributed to the fact that the right lobe poal laminar blood flow is supplied predominantly by the superior mesenteric vein, whereas the left lobe poal blood flow is supplied by the splenic vein.