THE MITES 



109 



time of the year are more exposed to mud and slush, bringing about a 

 macerated and inflammator}^ condition of the skin that favors the 

 multipHcation of the mites. 



Lesions. — Shortly after the invasion an abundant epidermic des- 

 quamation is noticed among the hairs and over the skin. Tufts of 

 hair are easily pulled out, and patches appear where the skin is bare and 

 smooth. Later crusts form over a thickened and exudmg skin, which 

 in the hollow of the pastern becomes fissured and bleeding. 



Diagnosis. — In view of the special seat of chorioptic scabies, other 

 parts not bemg involved, it is scarcely nec- 

 essary to confirm its differentiation from 

 other forms by the recovery of the mite. It 

 is important, however, to know whether 

 the case is truly one of scabies, and this 

 diagnosis can only be established with cer- 

 tainty by findmg the parasite. If present 

 it will be easih' found among the deeper 

 parts of the crusts and epidermic scales. 



Prognosis and Transmission. — Foot 

 scab is less infectious and is accompanied 

 by less itching than the other forms. The 

 prognosis is also more favorable, since, ex- 

 ceptmg in rare cases, the disease is confined 

 to the lower parts of the legs and usually 

 to the hind legs onl}'. Again, unlike other 

 scabies, it has little if any general effect 

 upon the animal. It yields readily to suit- 

 able treatment, and it is not hkely that 

 horses recei\'ing proper care as to cleanli- 

 ness of the hair and skin will be attacked, 

 even though exposed to the infection. Its 

 transmission from animal to animal in the 

 same stable is usually bv bedding and 

 grooming utensils in the hands of careless 

 attendants. 



Fig. 67. — Chorioptes communis 

 var. equi, female; ventral view. 



Scabies of the Sheep 



Sheep may be affected with the following forms of scabies, the first 

 mentioned being by far the most important in this animal : 



1. Psoroptic scabies, due to Psoroptes communis, var. ovis. 



2. Sarcoptic mange, due to Sarcoptes scabiei, var. ovis. 



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



4. Folhcular mange due to Demodex follicidorum, var. ovis. 

 Psoroptic Scabies of Sheep. — Through its exten.sive prevalence 



