Parasites and Parasitic Diseases of Sheep. 1 
Life history—The female mite usually deposits at least 15 eggs 
during her life, and may deposit 24. In 3 or 4 days these hatch, 
the young mites beginning life with only 6 legs. In 7 or 8 days 
these have become 8-legged mites, which mate and begin deposit- 
ing eggs in the course of the next 3 or 4 days. One investigator 
(Gerlach) has estimated that in 90 days this rate of reproduction 
under favorable circumstances, beginning with a single impreg- 
nated female, would produce one and one-half million mites. 
Distribution—Scab was formerly widely distributed over the 
United States, being the greatest pest that sheepmen had to con- 
tend with. Quarantine and eradicative dippings have nearly 
cleaned it out of the greater part of this country, so that at present 
Fic. 6.—Characteristic scab lesion in early stages of the disease. (From Imes, 1916.) 
it is largely a matter of cleaning up the relatively small amount 
that is scattered about, an exceedingly difficult task, however, be- 
cause of the scattered condition of the infection. The cooperation 
of individual owners in promptly reporting to local livestock sani- 
tary authorities cases of scab or cases suggestive of scab is hithly 
important in scab eradication. 
Symptoms and lesions.—The scab mite pricks the skin and sucks 
the blood serum. ‘The puncture becomes inflamed, forming a small 
red spot with a slight exudation of serum. This serum forms the 
scab, from which the disease takes its name (fig. 6). The watery 
part of the serum dries out, leaving a small crust for each bite, the 
total aggregate of these bites leading to the formation of consider- 
able crusts or scabs. At the same time the bite of the mite causes 
itching, and this in turn leads to scratching, rubbing, and biting, 
