104 



PARASITES OF THE DOMESTIC ANIMALS 



There is but one species, Demodex folliculorum (Fig. 70), which][in- 

 habits the hair foUicles and sebaceous glands of several mammahan 

 species. Its size differs somewhat with its habitat, the difference_^in 

 dimensions authorizing a division into varieties according to host. ' 



Scabies of the Horse 



Horses, asses, and mules are affected with one form of mange and two 

 of true scabies, as follows: -^ 



1. Sarcoptic mange, due. to Sarcoptes scabiei var. equi. 



2. Psoroptic scabies, due to Psoroptes communis var. equi. . ; 



3. Chorioptic scabies, due to Chorioptes communis var. equi, 



Sarcoptic Mange of the Horse. — In the majority of cases acariasis^of 



the horse is caused by Sarcoptes (Fig. 64). It begins most frequently 



Fig. 64. — Sarcoptes scabiei var. equi, female; dorsal (left) and ventral 

 (right) surface. 



about the head, sides of the neck, or at the withers, extending, if neg- 

 lected, over large areas of the body, involving in some cases even the 

 lower parts of the legs. In its initial stage sarcoptic mange is somewhat 

 slow in development, the small number of acari at the beginning not 

 giving rise to symptoms readily observable. In from three to six weeks, 

 however, the multiplication of the parasites has sufficiently progressed 

 to clearly reveal the affection. 



Symptoms. — The first symptom is itching, more or less intense, 

 which the animal seeks to relieve by rubbing itself against anything 

 available, or by biting affected parts of the body which it can reach. 



