532 HORSE, SWINE AND POULTRY DISEASES 



with a magnifying glass will serve to clear up doubtful cases. .(F. 

 B. 379.) 



LIVER FLUKE. 



The common liver fluke, (Fasciola hepatica, Linn), is more 

 common in cattle and sheep than it is in hogs. Liver flukes are ap- 

 parently of little importance in hogs in this country. They may 

 affect other organs besides the liver, but this is the chief abode of 

 the parasite. It is generally found in low lands and is more prev- 

 alent on wet than on dry years. 



Life History of Fluke and Method of Infection. Although 

 the life history of fluke is of little importance to us at present, 

 it is well for us to know something about their development. Their 

 life history in brief is as follows : Each adult worm is capable of pro- 

 ducing an immense number of eggs (thirty-seven to forty-five thou- 

 sand). These pass down the biliary passages into the intestines and 

 become mixed with the faeces. Those that reach some favorable 

 place for development after a long or short period of incubation 

 (from ten days to three months) depending on the amount of heat 

 and moisture, become a ciliated embryo. The ciliated embryo 

 swims in the water and seeks certain snails, penetrates into the res- 

 piratory cavity of these animals and encysts. The sporocyst, which 

 it is now called, at the end of about fourteen days is about one fifti- 

 eth of an inch in length, and the germ cells present develop into a 

 third generation, known as rediae. The rediae escape from the spo- 

 rocyst when the latter is from two to four weeks old. They then 

 wander to the liver of the snail and from the germ cells present in 

 the body cavity of the parasite develop the next generation, the cer- 

 cariae. This latter form resembles the adult parasite. It may re- 

 main in the body of the snail for some time or pass out and attach 

 itself on the grass or aquatic plants around the margins of the pond 

 and encyst. The different animals become infected from eating 

 these snails along with the food, or from eating grass infested with the 

 tercariae. The development will last from ten to twelve weeks. 

 Each sporocyst may give rise to from five to eight rediae, and each 

 rediae to from twelve to twenty cercariae. 



Lesions and Symptoms. These are directly dependent on the 

 presence of the flukes in the body, and as the liver is the organ gen- 

 erally affected and the chief abode of the parasites, the principal 

 lesions are in this organ. The flukes are confined to the gall ducts, 

 but may pass out into the proper tissue of the liver. There is a 

 catarrhal inflammation of the bile ducts. The smaller ones may be- 

 come dilated and form cysts. The inflammatory processes extend 

 from the ducts to the connected tissue of the liver and it becomes 

 hypertrophied and the liver cells are destroyed to some extent, de- 

 pending on the amount of infection, and a large portion of the 

 liver is a mass of cicatricial tissue. The gall is changed in char- 

 acter, is less thick, greenish brown or dirty red in color and contains 

 liver cells, blood cells, etc. These changes in the liver and in other 

 organs as well, lead to changes in the body nutrition and the animal 

 may become anemic, weak and emaciated. (Ind. B. 100.) 



