558 Protozoa of the Digestive and Urogenital Tracts 



developing fibrous tissue to limit the area of invasion. Instead, there is a 

 gradual transition from the surrounding normal tissue to the completely 

 necrotic tissue at the margin of the ulcer. The amoebae are usually most 

 numerous in the intermediate zone. If secondary bacterial invasion oc- 

 curs, as is the case fairly often, typical inflammatory reactions modify the 

 histological picture considerably. 



Extension of the ulcer may involve increase in depth and in diameter. 

 Penetration may continue through the muscularis mucosae and sometimes 

 even to the serosa, to be followed occasionally by perforation, or by local 

 adhesion of the colon to some adjacent structure. Individual ulcers may 

 heal spontaneously after a time, with a resultant fibrosis of the gut wall 

 and a variable amount of epithelial regeneration. In chronic infections, 

 this fibrosis, primarily of the submucosa and muscularis, may lead to 

 extensive thickening of the colonic wall, either locally or sometimes 

 throughout much of its length. 



Complications include perforations of the colon or the appendix, ab- 

 scesses of the appendix, perirectal abscesses, adhesions of the colon, 

 fistulae of amoebic origin, and sometimes amoebic granuloma of the 

 colon simulating carcinoma. A number of these complications, as en- 

 countered in a group of 20,000 patients, have been listed by Musgrave 

 (125). 



Secondary sites of infection may be established by migration of E. 

 histolytica from the colon into the ileum, or more commonly, by circula- 

 tory transportation of the amoebae. Upon entering the capillaries of the 

 portal system, the amoebae would pass first to the liver. From this organ, 

 they might be carried to the heart and to the lungs, and then perhaps 

 back to the heart and out in the systemic circulation. 



Amoebic abscess of the liver is the most common secondary lesion, al- 

 though the incidence has varied from less than 1.0 to about 50 per cent 

 in different groups of patients. Liver abscess may follow acute primary 

 amoebiasis or may develop in patients with no previous history of diar- 

 rheic amoebiasis or dysentery. Factors influencing the occurrence of liver 

 abscess are unknown. Such abscesses may be multiple or single, small or 

 large, and occur most frequently in the right lobe of the liver. Complica- 

 tions may result from rupture of a liver abscess into the peritoneal cavity, 

 or following adhesions, into the pleural cavity, into the stomach, or 

 thiough the body wall. Considerable progress is being made in the recog- 

 nition of hepatic amoebiasis in its early stages (151), and such early 

 symptoms as hepatic enlargement and tenderness have been correlated 

 with laboratory diagnoses. Since these early conditions seem to be cleared 

 up by chemotherapy, their recognition and characterization represent 

 a real advance in the control of secondary amoebiasis. 



A pulmonary abscess may be initiated by rupture of a liver abscess 

 into the pleural cavity, or by transportation of the amoebae through the 



