104 



PARASITES OF THE DOMESTIC ANIIVIALS 



There is but one species, Demodex follicidorum (Fig. 70), which in- 

 habits the hair folhcles and sebaceous glands of several manunalian 

 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 Sar copies 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 s\miptoms readily observable. In from three to six weeks, 

 however, the multiplication of the parasites has sufficiently progressed 

 to clearlj' reveal the affection. 



Symptoms. — The first sjanptom 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. 



