10 



SHEEP-SCAB. 



Definition. — A disease of the skin caused by certain members 

 of a class of small insects known as acari. 



Animals affected. — Scab is popularly known in animals otber 

 than sheep' as Mange. The parasites which cause Mange belong 

 to the same family as those which cause Scab, but they are a 

 different rariety. In sheep three forms of Scab are met with. 

 Psoroptic Scab, due to the " Psoroptis Communis " is the most 

 common form found in sheep. Sarcoptic Scab or Mange, due 

 to the " Sarcoptes Scabei var. ovis," occurs in sheep, but it is 

 rare. 



Symbiotic (Scab) Mange is also known. 



The Sarcoptic parasites will live on other animals and on 

 human beings. They cause severe symptoms ; the other para- 

 sites only live on man for a few days, causing temporary irrita- 

 tion. 



Sym^ptovis. — Psoroptic Scab begins on the less woolly or hairy 

 parts, but it soon spreads to other parts of the body. The first 

 symptoms appear in about three weeks after infection. During 

 the cold weather, however, the incubation period may be longer, 

 as the eggs hatch out more slowly, and the symptoms in the 

 latter case are not so marked. Still, it is a fact that in this 

 country a greater number of Scab cases occur in the cold season, 

 possibly because less dipping takes place and the sheep are more 

 croTvded together for warmth. The animals rub themselves 

 against fixed objects and show signs of satisfaction when 

 scratched with the hand. If the wool be parted, the skin 

 underneath is seen to be red in patches. Small pimples, from 

 which a thick fluid exudes, are found on the skin. This fluid 

 coagulates, and forms scabs which agglutinate the wool. The 

 constant biting at the skin and rubbing against fixed objects 

 cause the wool to drop off, and give rise to extensive sores. If 

 the animals are not treated, they become emaciated, and many 

 of them die of exhaustion. 



Sarcoptic Scab in sheep appears on the head and ears. 

 Sometimes it is seen on the tails of large-tailed sheep. It 

 gives rise to a formation of thick yellow crusts. Symbiotic 

 Mange appears usually at the lower parts of the limbs — about 

 the pasterns and coronets — and at the base of the tail. The 

 symptoms are not severe, but the animals rub their legs and 

 tails, and the wool becomes broken. 



If a scraping be taken from the diseased patches and placed 

 in the sun the moving parasites can often be seen with a 

 magnifying glass. 



