476 PARASITIC SKIN DISEASES 



are quite small and can only be recognized when highly 

 magnified. 



Sarcoptes Mite. This is the most common mange mite 

 and is distinguished by its tortoise-like appearance, an 

 elongated horseshoe-shaped head, and four pairs of short, 

 thick legs. In the male, which is the smaller, the first and 

 fourth pairs of legs are provided with a distinct cup-shaped 

 disk, but only the first and second pairs are so provided in 

 the female. The other legs are each supplied with a long 

 bristle. These parasites make burrows in the skin where they 

 live and obtain nourishment and in which the female deposits 

 eggs. The eggs hatch in five to eight days and the parasite 

 is fully developed in two to three weeks. They increase 

 rapidly. It is estimated that a million and a half are pro- 

 duced in three months, under favorable conditions, from a 

 single female. The sarcoptes mite varies slightly in size and 

 minor details according to the species of animal upon which 

 it lives. This makes several varieties which are sometimes 

 described as so many species. Most of the sarcoptes mites 

 live exclusively on their particular host, but, due to intimate 

 association, may be found occasionally on others. 



Pathology. The skin shows symptoms of chronic inflam- 

 mation varied according to the severity of the attack. In 

 mild cases dry crusts and scales cover the surface while the 

 severe ones show a much wrinkled and sometimes moist 

 surface. Fresh, bleeding areas may be associated with the 

 condition as the result of scratching or rubbing the part. 



Sarcoptes Mite of the Dog (Sarcoptes scabiei, variety canis). 

 -This is the common mite found on the dog. Sarcoptic 

 scabies may appear on any part of the body but usually 

 around the head. If unchecked it gradually spreads, becom- 

 ing generalized in four to eight weeks. Scratching and rub- 

 bing induced by the intense pruritus are the first noticeable 

 symptoms. Small red spots appear followed by papules and 

 pustules and these, ruptured by scratching, lead to formation 

 of moist areas which continue to spread. The areas first 

 invaded soon become dry. Yellowish-gray crusts form and 

 gradually scale off. The hair falls out during the process. 

 The skin becomes thickened and shows wrinkles and thick 



