CHAPTER XIX 



ANIMAL PARASITES AND PARASITIC DISEASES 



GENERAL CONSIDERATIONS 



All animal parasites attacking domestic animals belong to the 

 invertebrates. They are living organisms which obtain their sus- 

 tenance in whole or in part from their host — the animal they 

 infest. 



The occurrence of parasites is more frequent than is generally 

 recognized. All species of farm animals are attacked. Often 

 quite badly infested cases are overlooked because the parasites 

 are so small that they escape notice or are not looked for 

 intelligently. 



The effects of parasitism depend on the kind, number, and 

 position of the invaders. Injury is caused by animal parasites 

 from irritation; from drain by feeding upon the tissues and juices; 

 from poisoning caused by toxins produced by the parasites; from 

 their wanderings in and destruction of the body tissues; from in- 

 terference with absorption in the intestines; from obstruction of 

 the natural passages of the body. 



The diseases produced by parasites are quite numerous. The 

 most common are: pneumonia, bronchitis, indigestion, colic, liver 

 rot, gid, measles, mange, lousiness, and Texas fever. Greater 

 losses occur in the south than in the north where the early and 

 late frosts and rigorous winters destroy the eggs and larvae. 

 Sheep are more subject to attack by animal parasites than other 

 species of farm animals because they are less resistant; eat the 

 grass closer to the ground, thus having a greater opportunity to 

 pick up eggs; and afford protection to external parasites by their 

 heavy fleeces. 



The symptoms of parasitism vary with the position of the para- 

 sites. External parasites may cause the following symptoms: 

 itching, dry skin, rough hair, loss of hair. Internal parasites 

 may cause: unthriftiness, emaciation, malnutrition, constipation 



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