PARASITES AND PARASITIC DISEASES OF HORSES 47 



and bite themselves to relieve the intense itching, and these symptoms 

 should always be investigated to learn the cause. 



As the mites multiply, large numbers of small wounds are made in 

 the skin, followed by the formation of papules, increased inflammation 

 and itching, and the exudation of serum. The serum which oozes to 

 the surface becomes mixed with foreign matter and microorganisms, 

 and this mass soon hardens into yellowish or gray-colored scabs. The 

 scabs are frequently stained with blood. In the early stages the hairs 

 around the lesion may be glued together in a small clump and the 

 nodule or scab may be about the size of a pea. As the mites con- 

 stantly seek the healthy skin around the edges of the wound, the scab 

 or lesion gradually increases in size. 



Some of the mites migrate to other locations and start new lesions, 

 which extend until they cover large areas. As the disease advances 

 the skin becomes thickened, tumefied, and thrown into wrinkles or 

 folds. Large areas become denuded of hair and covered with thick, 

 adherent scabs. When the disease reaches this stage it is difficult to 

 differentiate it from sarcoptic mange. « 



Itching is intense and irritation continues throughout the course 

 of the disease. The skin becomes bruised and raw from the reckless 

 rubbing against any available surface. The uniform thickening and 

 hardening of the skin is characteristic of mange, but the most certain 

 diagnosis consists in finding and identifying the mite which causes the 

 disease. In the early stages of psoroptic mange the mites may usually 

 be found in scrapings taken with a blunt-edged knife from around the 

 edges of fresh lesions. In the advanced stages scrapings taken from 

 the edges of scabs or from the bottoms of the folds of skin may contain 

 mites. 



In the early stages psoroptic mange may be distinguished from 

 sarcoptic mange by the character of the lesions and the manner of 

 spreading, but the most dependable diagnosis consists in finding the 

 mite. For practical purposes where facilities for examination are 

 limited the principal differences in form and structure of the two 

 species of mites may be summarized thus: The sarcoptic mite is 

 slightly smaller than the psoroptic mite, and the body of the former is 

 more nearly round than oval (fig. 27). Adults of both species have 

 four pairs of legs, those of the psoroptic mites being long, and all four 

 pairs extend beyond the margin of the body (fig. 30). The sarcoptic 

 mites have shorter legs, and the fourth or hind pair and usually the 

 third pair do not extend beyond the margin of the body. The head 

 of the common scab mite is tapering or cone-shaped and is longer than 

 it is broad, whereas that of the psoroptic variety is bluntly rounded in 

 front and is as broad as it is long. 



It is advisable to examine several specimens in all cases, because 

 under low-power magnifying glasses the females of the two species 

 are more easily distinguished from one another than the males. On 

 account of the burrowing habits of the sarcoptic mites, they are diffi- 

 cult to find, especially in the early stages of the disease. They are 

 situated in burrows under conical papillae, and by scraping the 

 infested area until the blood oozes from the tissue, the mites sometimes 

 may be found in the scrapings. 



