276 DISEASES OF THE SKIN 



Neither sheep nor other animals can be infected by natural 

 or artificial means. While some outbreaks are comparatively 

 mild, not infrequently the affection assumes a malignant 

 form which leads to considerable losses, causing it to become 

 a matter of importance to sheepmen. 



Etiology. — The cause of bighead has not yet been deter- 

 mined. Outbreaks occur usually during the spring and early 

 summer while the sheep are being driven from the winter to 

 the summer ranges and before they are sheared. Climatic 

 conditions evidently predispose to the disorder, which is most 

 apt to appear following a cold, stormy night, especially if the 

 sheep are driven the next day in the hot sunshine. The dis- 

 ease is most apt to affect adult sheep; it is rarely seen in 

 young lambs. The condition of the sheep seems to have little 

 to do with the occurrence of an outbreak; it is as apt to 

 attack the well nourished as it is individuals poor in flesh. 

 Buckwheat feeding has failed to produce in experimental 

 animals symptoms of the disorder. 



Symptoms. — The symptoms which precede the appearance 

 of the swellings are jerking movements of the head; the sheep 

 shakes its head and rubs it against objects. The eyesight 

 seems to be impaired, the sheep often running into other 

 sheep and objects found in its path. Symptoms of cerebral 

 excitement are not uncommon, in some instances the sheep 

 show maniacal phenomena. Obviously sheep so affected often 

 leave the flock, become lost, and die of exhaustion and ex- 

 posure, or become the prey of coyotes. 



Later it will be noted that the ears begin to turn red and 

 become swollen. Finally the swellings extend over the cheeks 

 and face, closing the eyes, or in some cases, if the retrobulbar 

 tissue becomes involved, may force the eyeballs from their 

 sockets. The swellings may become very tense and drops of 

 serum ooze from them. In some cases the lips, cheeks, and 

 tongue are so swollen that it is impossible for the animal to 

 eat or drink. Dyspnea is a common symptom. The tem- 

 perature ranges from 104° to 107° F. The skin often sloughs 

 over the swollen areas, and the wool over the entire body may 

 be shed. Pregnant ewes frequently abort. Sheep which 

 recover are usually left permanently unthrifty. 



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