THE LIVER FLUKE DISEASE— DISTOMATOSIS 147 



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 

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

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

 ' lanceolatum (Fasciola lanceolata) . 



Natural History. — The eggs of Distomum 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 radise. From the radiee pass out the 

 cercarise. The cercarise swim about in water and attach 

 themselves to blades of grass, in 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 from 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 five to six weeks. From the 

 gall ducts, in which they have produced chronic inflammation 

 and dilatation, they pass into the liver substance. 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 circulation occasionally happens, 

 which accounts for their appearance in newborn calves. 



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