Etiology. Pathogenesis. 935 



here develop protected by the hairy covering or hidden between 

 the folds of hair. The most varied objects, when coming in con- 

 tact with the affected skin or when touching the encrusted parts, 

 but especially cloths and harness, are frequently the media of 

 infection. Infection by immediate contact happens mostly when 

 many animals live close to or in contact with one another, as 

 for instance sheep, pigs, hounds, further in narrow stables or 

 in horses worked in pairs where the mites can wander from the 

 body of one animal to that of another. 



The infection is the easier, the more undisturbed the mites 

 can live on the skin. Among sheep the disease may on this ac- 

 count very easily assume an enzootic character, since the mites 

 can remain undisturbed in the depths of the close fleece. In other 

 animals the development and spread of the skin affection occurs 

 the more quickly the poorer the skin hygiene, and with this the 

 experience coincides, which finds scab the more severe the poorer 

 the owner, while on the bodies of well cared horses it occurs 

 less often, and does not attain such great extension. Here clean- 

 ing and curry-combing hinder the settlement of the parasites, 

 and sometimes after a successful infection a portion of the mites 

 are later removed from the skin. Other skin diseases and de- 

 Inlitating influences greatly predispose the body to the com- 

 plaint. 



Susceptibility. Scab generally spreads easily and quickly 

 only in animals of the same species, while infection from one 

 species to another occurs much more rarely. 



With reference to the direct infection of individual species of animals, and of 

 animals and man, the following was noticed (principally from the statistics of 

 Friedberger & Frohner) : 



All varieties of sarcoptes of domestic animals are communicable to man. 

 Sareoptic scab of man, sheep, dogs, cats, pigs, camels and rabbits is communicable 

 to the horse. 



Sarcoptic scab of horses, sheep, goats, cats and pigs (personal observation) 

 is communicable to cattle. 



Sheep can be affected with sarcoptic scab by dogs and goats. 



Dogs can be affected with the sarcoptic scab of man, pigs, cats, goats, sheep 

 and foxes. 



Pigs may be infected l)y sarcoptic scab of goats. 



The sarcoptic scab of man may be transmitted to rabbits. 



While therefore the possil)ility of transmission of sarcop- 

 tic scab to other species of animals exists, the affection arising 

 thus is sometimes of a mild and transient character, but in 

 other cases severe disease has been noted. It appears that the 

 dermatocoptes and dermatophagus scab cannot be transmitted 

 from one species of animal to another ; at most the mites cause 

 transitory itching. 



Pathogenesis. The sarcoptes mites usually localize on that 

 part of the skin on which they happen to get foothold, while the 

 dermatocoptes mites living on the surface of the skin, and con- 

 sequently little protected, seek out the more protected parts, or 

 the dermatophages seek out the skin of the extremities or the 



