PREVENTIVE MEDICINE 365 



of dogs, the kennels, baskets, rugs, &c., should be thoroughly dis- 

 infected. 



PSOROPTIC MANGE OF SHEEP. SHEEP SCAB. 



Sheep-scab, due to the presence on the skin of Psoroptes 

 commnnis v. ovis, is the cause of considerable financial loss to 

 sheep owners. Badly infected sheep fail to thrive owing to the 

 continuous pruritis and want of rest. There is considerable 

 damage done to the fleece and, as is to be expected, a general 

 depreciation in value of the flocks. There is additional loss 

 resulting from the time and labour expended in dipping and carry- 

 ing out the regulations enforced to combat this preventable disease. 



The regions primarily affected are the back, withers and rump, 

 but, if neglected, the mites spread until eventually the whole body 

 becomes affected. The disease is more prevalent in cold than in 

 warm weather, and removal of the fleece may have an inhibiting 

 action on the activity of the mites. It is well known that 

 psoroptes can, and frequently do, remain in a quiescent state for 

 several months, and isolated clumps of acari may be detected in and 

 about the ears and at the root of the tail in sheep which are not 

 suspected of being scab-infected. Such sheep may act as carriers 

 and spreaders of the disease without the flockmaster having any 

 suspicion of the fact. In connection with this most important 

 point the Chief Veterinary Officer of the Board of Agriculture 

 says* that the acari of sheep scab can remain on a sheep for long 

 periods without producing noticeable symptoms of the disease. 

 Herein lies one of the chief difficulties of eradicating the disease. 

 The same authority points out that a sheep but slightly affected, or 

 one insufficiently dipped, may remain healthy in appearance for 2 

 or 3 months and then become visibly affected. It is further 

 stated that such recurrences usually take place in the autumn or 

 winter; thus scab may appear without any apparent reason on a 

 supposedly clean farm. It is, furthermore, not possible by any 

 practicable means to detect scab on animals but mildly affected 

 or on such as act as carriers. Other conditions which cause 

 dermatitis and pruritis may also mask a dual infection. 



It is said that acari have been found to live away from sheep for 

 a month to six weeks at the longest, but most of them die sooner 

 than this. Eggs have been observed to hatch out two or even four 

 weeks after removal from the sheep, but the majority hatch in a 

 few days. The duration of the whole life-cycle is given as from 

 12 to 16 days, 23 days being the longest by calculation (Stockman). 



* Cd, 7423. 



