DISEASES OF SHEEP 529 



Description of Common Sheep Scab. The mites of common, 

 or body, scab that is, the Psoroptes prick the skin of the animal 

 to obtain their food, and probably insert a poisonous saliva in the 

 wound. Their bites are followed by intense itching, with irritation, 

 formation of papules, inflammation, exudation of serum, and the 

 formation of crusts, or scabs, under and near the edge of which the 

 parasites live. As the parasites multiply they seek the more healthy 

 parts, spreading from the edges of the scab already formed, thus 

 extending the disease. The sheep are restless; they scratch and bite 

 themselves, and rub against posts, fences, or stones, or against other 

 members of the flock. This irritation is particularly noticeable 

 after the animals have been driven, for the itching is more intense 

 when the sheep become heated. The changes in the skin naturally 

 result in the falling of the wool. At first slender tags are noticed ; 

 the fleece assumes the condition known as flowering; it looks tufty 

 or matted, and the sheep pulls out portions with its mouth, or leaves 

 tags on the objects against which it rubs. Scabs fall and are re- 

 placed by thicker and more adherent crusts. The skin finally be- 

 comes more or less bare, parchment-like, greatly thickened, fur- 

 rowed, and bleeding in the cracks. With shorn sheep, especially, a 

 thick, dry, parchment-like crust covers the greatly tumefied skin. 

 Ewes may abort or bear weak lambs. 



PARTS OF BODY AFFECTED BY SCAB. 



When sheep are kept in large numbers the chances for infection 

 are naturally greater, and the disease may begin on almost any 

 part of the body. Generally, however, it affects the parts which are 

 covered with wool. When the sheep are fat and the wool has a large 

 amount of yolk, the progress of the disease may be slow ; usually be- 

 ginning on the upper part of the body, withers, and back, it extends 

 slowly, but none the less surely and in ever-increasing areas, to the 

 neck, sides, flanks, rump, etc. In two or three months the entire 

 body may be affected. 



CONTAGIOUSNESS OF SCAB. 



Common scab is exceedingly contagious from one sheep to an- 

 other, and may in some cases show itself within about a week after 

 healthy sheep have been exposed to infection. The contagion may 

 be direct, by contact of one sheep with another; or indirect, from 

 tags of wool, or from fences, posts, etc., against which scabby sheep 

 have rubbed, or from the places where the sheep have been bedded 

 down. One attack of scab does not protect sheep from later attacks. 

 Transmitted to man, sheep scab may produce a slight spot on the 

 skin, a point which is sometimes taken advantage of for the purpose 

 of diagnosis. In case of suspected scab, one of the crusts is bound 

 lightly on the arm. After a short time an itching sensation is felt 

 and the mites are found on the skin. Transmitted to horses, cattle, 

 or goats, common sheep scab fails to develop. 



Chances for Recovery From Scab. Cases of apparent spontane- 

 ous recovery are rare. Usually when proper methods of treatment 

 are not adopted the disease increases, leads to anaemia, emaciation, 

 exhaustion, and death, and may result in a loss of from 10 to 80. per 



