170 DISEASES OF THE LIVER 



Natural History. — ^The echinococcus cyst is the larva of 

 the Taenia echinococcus, a tapeworm of the dog. The 

 segments of the tapeworm are voided with the feces of the 

 dog, polluting stables and pastures where they are taken up 

 by herbivorous animals. The embryos which hatch from 

 the eggs in the stomach and intestines of the new host 

 wander into the bile ducts and portal circulation of the 

 liver in which organ they form cysts some of which contain 

 scolices. The cysts vary in size from a pea to a himian 

 head. In turn if a liver containing the cysts is eaten by a 

 dog there develops in the intestines of the dog the parent 

 tapeworm, the Taenia echinococcus. 



Two varieties of Taenia echinococcus have been deter- 

 mined: (a) The Echinococcus unilocularis which is the 

 most common form and usually found in sheep. This cyst 

 forms a simple cyst or there may be adherent to a 

 principal cyst secondary or tertiary cysts, (b) The Echino- 

 coccus m unilocular is. This cyst is comparatively rare and 

 is found in cattle. It has no capsule but forms in the liver 

 a proliferating tumor containing many lacunae" and macro- 

 scopically resembles somewhat a carcinoma. 



Besides the liver the echinococcus may invade the lung, 

 heart, muscle, brain and peritoneum, or even occasionally 

 bone or cartilage (the sternum). 



■ Symptoms. — The symptoms produced by the presence of 

 this parasite in the liver are usually very vague. In cattle 

 notwithstanding a great development of cysts in the liver 

 the animals usually appear perfectly healthy. In general 

 the symptoms are those of a chronic digestive disturbance 

 and emaciation. Sometimes the animals show sensitiveness 

 over the region of the liver and on percussion an increase 

 in the area of hepatic dulness. On rectal examination 

 sometimes the enlarged nodular liver may be felt. In indi- 

 vidual cases chronic bloating may result as in mediastinal 

 tuberculosis causing compression of the gullet. In swine 

 ascites is an occasional symptom. In very rare instances 

 the rupture of superficial cysts causes fatal peritonitis. 

 Recent application of the complement-fixation test, using 

 the fluid contained in the cysts as the antigen, has demon- 

 strated that it is valuable in diagnosis. 



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