72 PARASITES OF THE DOMESTIC ANIMALS 



necessarih' resulting from, but rather predisposing to the attack, the 

 reduction in the functional activity of the skin in such condition afford- 

 ing an inviting habitat for the parasites. Herbivorous animals which 

 have been kept for a prolonged period upon dry feed, as during the 

 winter months, are those most likely to be infested, lice rarely being 

 found upon these animals after they have been turned upon more 

 succulent food and the winter coat has been shed. 



There is, in fact, little valid excuse for the presence of these parasites 

 upon our domestic animals at any time. Infestation is usually the 

 accompaniment of uncleanly, impoverished, and crowded conditions of 

 stabling or yarding. Well housed, well fed, and regularly groomed 

 animals offer no attractions to lice, and animals so cared for will not 

 have them. Excepting in accidental and transient incidents, their pres- 

 ence upon man or domesticated beast reflects upon man in either case. 



Whether the degree of discomfort and injury to an animal due to the 

 presence of lice upon its l)ody is slight or serious in its consequences will 

 depend upon the number present and the group to which thej^ belong. 

 The sucking lice, piercing the skin and feeding upon the blood and 

 exudate, cause a much more intense pruritus than that occasioned by 

 the biting lice which, in their habit of feeding upon surface epidermic 

 products and debris, have more the nature of scavengers. 



The presence of the lice, as well as their location, is indicated by the 

 pruritus, by their eggs or nits upon the hairs, and the debris of their 

 molts. The irritation of the itching and rubbing, together with the loss 

 of blood if suctorial lice are numerous, results in emaciation and general 

 unthriftiness of an animal likely to have ])een in poor condition before 

 becoming infested. 



While the presence of lice may be unmistakably evident, it should 

 be made quite sure that there is not also present a form of acariasis. 

 Lice fi-equently invade animals suffering from scabies, and the pruritus, 

 with the accompanying scaly and scabby condition of the skin, may be 

 due to scab mites, which, minute and deeply located, may be readily 

 overlooked. The presence of these can only be determined with cer- 

 tainty by examination of epidermic scrapings from beneath the scabs. 

 For their detection and examination the microscope is necessai;;y'. They 

 are, however, often difficult to discover, and the material is best sub- 

 mitted to a laboratory for examination if such is available. More de- 

 tailed methods of diagnosis and treatment of this condition are given 

 elsewhere under the discussion of the scab mites. 



Pediculosis of the Horse 



Horses, mules, and asses harbor one species of sucking louse, Hcema- 

 topinus asini, and two species of biting lice, Trichodectes equi and T. 

 pilosus. 



