280 DISEASES OF THE SKIN 



in every country. When large numbers of animals are con- 

 gregated as are sheep on the western ranges, or horses and 

 mules in time of war, the disease often assumes the character 

 of an enzootic. During the Great War, and until proper 

 remedial agents were employed to combat it, fully 40 per cent, 

 of the animals of the army became infested, unhorsing many 

 military units. While mange in its incipient stages is a local 

 disease, confined to restricted areas of the skin, under favor- 

 able circumstances it spreads over the entire body and leads 

 to dermatitis, itchiness, loss of hair, emaciation, anemia, 

 cachexia and sometimes death. While some varieties spread 

 over the surface of the skin more rapidly than do others, each 

 type of mange mite can, under favorable conditions, invade 

 the whole skin. 



Mange depends largely for its spread upon the fact that in 

 its beginning stage it is a local disease affecting only a small 

 area of the skin. The host may appear perfectly healthy, 

 perform its usual functions normally and at the same time 

 harbor a circimascribed area of mange which fails to attract 

 attention. Such an animal if allowed to commingle with 

 others will spread the disease. Under adverse circumstances, 

 especially during the winter season when animals are sub- 

 jected to rather unfavorable conditions as to feeding and care, 

 the mange mites multiply and the skin lesions increase until 

 marked symptoms of dermatitis develop. Ordinarily, there- 

 fore, methods of control and eradication are not employed 

 until a number of animals are affected and general symptoms 

 have developed. 



Definition. — Mange is a dermatitis produced by minute, 

 insect-like parasites, and attended by intense itching. 



Occurrence. — ^As mange is communicable it assumes at 

 times an enzootic or even epizootic distribution. This is 

 particularly true of the scabies of sheep, which in a single 

 state may affect thousands of animals, or, as noted, of horses 

 and mules in time of war. 



Etiology. — Mange is caused by a small mite which rarely 

 can be seen with the naked eye. 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. In most 



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