528 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



back to their hosts. By exercising vigilant care, a flock can be 

 entirely rid of this pest. 



THE SHEEP LOUSE. (TRICHODECTES SPHAEROCPHALUS.) 



This louse is exceedingly small and according to reports rarely 

 seen in this country. Prof. Osborn in his work on "Insects Affect- 

 ing Domestic Animals" states he has found it quite plentiful on 

 sheep coming from Canada. When present in large numbers, it 

 causes severe itching, rendering some remedy necessary. The use 

 of Pyrethrum powder or the regular dips will prove effectual. 



SCAB IN SHEEP. ( SCABIES ). 



Introduction. The disease commonly called sheep scab is one 

 of the oldest known, most prevalent, and most injurious maladies 

 which affect sheep. It is a contagious skin disease caused by a 

 parasitic mite. Investigation has shown that the disease is not he- 

 reditary, as the parasites which cause it live on the external surface 

 of the body. It is possible, however, for a lamb to become infected 

 from a scabby mother at the moment of birth or immediately after. 

 The treatment must consist of external applications for the destruc- 

 tion of the parasites and not internal remedies to purify the blood. 



The disease is one of the most serious drawbacks to the sheep 

 industry and results in enormous financial losses. The losses are 

 due to the shedding of the wool, failure of condition, and the death 

 of the sheep. Yet, despite its insidious nature, its ease of transmis- 

 sion, its severe effects, and its prevalence in certain localities, it is a 

 disease which yields readily to proper treatment. 



Cause of Common Sheep Scab. Sheep scab is a strictly con- 

 tagious disease. Common sheep scab is caused by that species of 

 mites technically known as Psoroptes communis. Parasites of this 

 species cause scab in horses, cattle, sheep, goats, and rabbits ; but for 

 each of these species of animals there appears to be a distinct variety 

 of this parasite. Although it is more or less difficult to distinguish 

 between these varieties, they differ somewhat in size ; also it is found 

 that the Psoroptes communis of the sheep does not cause scab of the 

 horse, ox, or rabbit ; nor, on the other hand, does the Psoroptes com- 

 munis of the horse, ox, or rabbit cause scab of the sheep. Natural- 

 ists, therefore, distinguish the parasite of sheep scab by the name 

 Psoroptes communis var. ovis. 



The parasite of this disease is one of the larger mites, and is 

 quite easily seen with the naked eye. The adult female is about 

 one-fortieth inch long and one-sixtieth inch broad; the male is 

 one-fiftieth inch long and one-eightieth inch broad. These mites 

 are discovered more readily and more clearly on a dark than on a 

 light background, and for that reason the crusts from the affected 

 skin are often placed upon black paper and kept in the sunshine 

 for a few minutes in order to reveal the parasites crawling about. 



The Psoropt inhabits the regions on the surface of the body 

 which are most thickly covered with wool that is, the back, the 

 sides, the rump, and the shoulders. Its presence is the cause of the 

 true body scab on sheep, and of all parasitic mites it produces the 

 most serious injuries. 



