SHEEP SCAB 133 



unthriftiness of the individual animal. When sheep are fat and 

 the wool is well supplied with yolk, this disease spreads more 

 slowly, and is much less serious. The infection is frequently 

 made when one sheep rubs against posts or fences where scabby 

 sheep have previously rubbed. In the latter case, the mites are 

 first transferred from the diseased sheep to the post, and then 

 from the post to the healthy sheep. In other cases, the mites 

 are transferred when a diseased sheep rubs against a healthy 

 one. 



Precautions. — Pens, sheds, and yards which have held scabby 

 slieej) should be thoroughly cleaned and disinfected; and, unless 

 tiie disinfection is very thorough, they should not be used for 

 sheep until at least four weeks have elapsed. It is supposed 

 that a hard rain will practically disinfect ground surfaces, but 

 not fences and posts. Fields and pastures in which scabby sheep 

 have been held should not be used again until after an interval 

 of several weeks, and preferably not until after a heavy rain. 



General Symptoms 



History and diagnosis. — At the point of infection there oc- 

 curs the puncture ; then a little pimple, soft on top, which rup- 

 tures, a little fluid escaping. Dust and other foreign matter 

 collect in this fluid, the initial scab is started, and the diseased 

 area spreads. 



Affected sheep are usually uneasy and are seen scratching 

 against posts, rubbing against other sheep, and even biting the 

 itching surface. The irritation is most noticeable when the 

 sheep are heated, as by exercise, or confined in a close room. 

 At first the wool hangs in tags, the sheep begin to pull out por- 

 tions of the wool with the mouth, and the skin becomes bare in 

 patches which increase as the mites spread, irritating and in- 

 flaming the skin. To determine the presence of the mites, scrape 

 off some of the scab and a little of the healthy skin near the 

 border of the scab. Place these scrapings upon some smooth 

 black surface in warm sunshine, and examine with a good hand 

 lens. The mites may then be seen as minute white bodies about 

 1/50 of an inch long. They are most certainly recognized when 

 they are seen to move. It is sometimes difficult to distinguish 

 otherwise betw'een the mites and particles of liglit-colored dust 

 or epithelial scales from the skin surface. One is more apt to 



