SHEEP SCAB. 197 



Exposure resistance. — The mites which cause foot scab and 

 body scab have considerable vitality, being able to withstand ex- 

 posure at moderate temperatures from one to two or even three 

 weeks under favorable conditions, possibly longer. They die 

 sooner in a dry atmosphere than moist. Cases are on record where 

 sheep seem to have become infected with scab in places where 

 sheep had not been kept for many months. The history of these 

 cases, however, is not well understood, and it is difficult to say 

 positively how long mites or their eggs ma}' preserve vitality under 

 favorable conditions. 



Precautions. — Scabby sheep should not be driven over any 

 public highway. Pens, sheds and yards which have held scabby 

 sheep should be thoroughly cleaned and disinfected, and unless 

 the disinfection is very thorough they should not lie 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 scab!))' sheep have 

 been held should not be used again until after an interval of sev- 

 eral weeks, and preferably not until after a heavy rain. 



GENERAL SYMPTOMS. 



History and diagnosis. — At the point of first infection there 

 appears a small, congested area, showing plainly the result of irri- 

 tation caused by the parasite, which has burrowed into the skin. 

 Then there appears a little pimple, soft on top, which ruptures and 

 a little fluid escapes. Dust and other foreign matter collect in this 

 fluid and the initial scab is started. 



Affected sheep are usually uneasy and are seen to scratch 

 against posts, rub against other sheep and even bite 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 is noticed to hang in tags, the sheep begin to pull out portions 

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

 patches which gradually increase as the mites spread, irritating 

 and inflaming 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. They 



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