SCABIES— MANGE—SCAB 259 



SCABIES. MANGE. SCAB. 



Definition. — Scabies is an eczema produced by minute 

 insects and attended by intense itching. 



Occurrence. — As scabies is contagious it assumes at times 

 an enzootic or even epizootic distribution. Particularly is 

 this true of the scabies of sheep, which in a single state may 

 affect thousands of animals and lead to great economic 

 losses. 



Etiology. — Scabies is caused by a small spider-like mite 

 which can rarely be seen with the naked eye, the mites 

 belonging to the order acarina, class arachnoidea. They 

 are from 0.2 to 0.8 mm. in size, provided with four pairs of 

 legs and an undivided trunk. The males are smaller than the 

 females. The females lay eggs which in about eight days 

 hatch six-legged larvae. In eight days the larvse become sex- 

 ually mature. The females live for three to five weeks, the 

 males about six weeks. Under favorable circumstances mites 

 may live as long as eight weeks, and under contrary condi- 

 tions as short a time as two weeks. Infestation may be from 

 direct contact or through intermediary agents, such as har- 

 ness, grooming utensils, blankets, bedding, etc. 



Varieties. — Three varieties of mites are distinguished: (a) 

 Sarcoptes, (b) Psoroptes, and (c) Symbiotes. A fourth 

 species, the follicle mite, is usually not included under the 

 mange mites. 



Sarcoptes Mite. — This is a burrowing parasite which lives 

 in the Malpighian layer of the skin where it forms tunnels 

 under the epidermis. It is the smallest species (0.2 to 0.5 

 mm.), shaped like a turtle, with a head like a horseshoe and 

 very short legs. Three varieties of sarcoptes occur in animals : 

 (a) Sarcoptes scabei of the horse, (b) Sarcoptes squamiferus 

 of the dog, and (c) Sarcoptes minor of the cat. 



Psoroptes, or Sucking Mite. — This minute insect lives 

 upon the surface of the skin, and is nourished by the blood 

 and lymph. It is the largest of the mites (0.5 to 0.8), and 

 under favorable circumstances (on black paper, for instance) 

 may be seen with the naked eye. Its head is pointed, legs 

 very long, and feet provided with tulip-shaped suckers. Two 



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