168 DISEASES OF THE LIVER 



THE LIVER FLUKE DISEASE. DISTOMATOSIS. 



Definition. — ^An inflammation of the liver and bile ducts 

 due to the presence of trematode parasites of the genus 

 fasciola. 



Occurrence. — The disease produced by these flukes is 

 commonly known as "liver rot" and sometimes assumes an 

 epizootic distribution, particularly among sheep, where it 

 causes considerable loss. The disease is sometimes noted 

 in cattle, but rarely attains in these animals economic im- 

 portance. There are two forms of liver fluke in animals: 

 (1) Distoma hepaticum (Fasciola hepatica), and (2) Distoma 

 lanceolatum (Fasciola lanceolata). 



Natural History. — The eggs of Distoma hepaticum reach 

 the outer world with the feces. On damp pastures and 

 under the influence of summer heat the embryo is hatched 

 in about one month. They then enter snails, in which in 

 about four weeks they become converted into sporocysts, 

 out of which there develop redise. From the redise pass out 

 the cercarise. The cercariee swim about in water and 

 attach themselves to blades of grass, on which they become 

 enclosed by a sticky substance. The infestation of the 

 animal occurs from eating the grass or forage or from the 

 drinking water containing these encysted cercarise. It is 

 possible for infestation to take place in the sheepfold either 

 fronr green food and water or probably from dry food. 

 After ingestion the parasites pass through the bile ducts, in 

 which they become sexually mature in from flve to sik weeks. 

 From the gall ducts, in which they have produced chronic 

 inflammation and dilatation, they pass into the liver sub- 

 stance. Here they induce hemorrhagic foci, multiple 

 abscesses and ultimately cirrhosis of the liver. In rare 

 instances they may perforate the capsule of the liver or 

 even the portal vascular system, causing phlebitis and 

 thrombosis. Sometimes they enter the lungs, inducing 

 hemorrhagic foci and encysted worm nodules may be found 

 in the bronchi. From the lungs they may enter the arterial 

 circulation and pass through it to all parts of the body. 

 A passage from the mother to the fetus through the placental 



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