LECTUEE XXVI 

 SHEEP SCAB 



Sheep scab is a result of irritation of the skin, caused by 

 mites, minute animal parasites that puncture the skin from 

 the surface or burrow tunnels in it. 



There are three common types of these mites and three types 

 of the disease which they cause. One variety of mites produces 

 body scab, another head scab, and a third foot scab. Body scab 

 is the most common, the others are relatively unimportant. 



Mites are permanent parasites, their entire life history being 

 spent on one host ; they multiply with enormous rapidity. 



Body Scab 



Body scab is caused by mites (Psoroptes) which have power of 

 free movement upon the surface. It is the most common and 

 serious type of scab. This type spreads most rapidly over the 

 individual body, and also rapidly through the flock and from 

 flock to flock. 



General history. — This disease is likely to become serious 

 before being noticed by the owner. The parasites which cause 

 this type of the disease do not tunnel into the skin, but cause 

 intense irritation, especially when the sheep are warm. The 

 owner will usuallj^ remember, after he has become aware that 

 body scab exists in his flock, that his sheep have seemed uneasy 

 and that they have been rubbing and biting themselves occa- 

 sionally for some time. 



After the disease is under way, the parasites live beneath the 

 crusts, and constantly migrate outward, while the skin slowly 

 heals in the center. The fleece of scabby sheep is usually rough, 

 and the wool matted in places and easily rubbed ofi'. The para- 

 sites which cause this form of the disease confine their work 

 almost exclusively to parts of the body where the wool is long 

 and thick. 



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