42 



CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



Horse Mange 



Scabies in horses, commonly known as mange, itch, or scab, is a 

 name given to a group of contagious skin diseases caused by minute 



parasites known as mites, which 

 live on or in the skin. Four species 

 of these parasites are found on 

 domesticated animals, but horses are 

 commonly affected by only three 

 of them. These parasites are classi- 

 fied zoologically in three different 

 genera — Sarcoptes, Psoroptes, and 

 Chorioptes. Mites of the first two 

 genera are shown in figures 27 

 and 30. 



In obtaining their food from the 

 host and preparing a resting place 

 in or on the tissues, the mites cause 

 wounds or lesions in the skin. As 

 each kind of mite possesses dis- 

 tinctive habits, the location and 

 nature of the lesions in the early 

 stages are more or less characteristic. 

 Each kind of mite, therefore, causes 

 a specific kind of mange which is 

 named after the generic name of the 

 mite. Thus we have in horses 

 sarcoptic, psoroptic, and chorioptic 

 mange. The sarcoptic variety is the one most common on horses in 

 the United States 



SARCOPTIC MANGE 



Figure 27. — Sarcoptic mange mite 

 Female. (Magnified 100 times.) 



SARCOPTIC MANGE MITE 



The mites which cause sarcoptic or common mange of horses are 

 small, white, or yellowish parasites known technically as Sarcoptes 

 scabiei equi (fig. 27). The female when full grown measures about 

 one-fiftieth and the male about one-sixtieth of an inch in length. When 

 placed on a dark background they are visible to the naked eye. The 

 general form of the body is more nearly round than oval, and the 

 bluntly rounded head is as broad as it is long. When mature, these 

 mites have four pairs of short, thick legs, the fourth pair and usually 

 the third pair also not extending beyond the margin of the body. 

 Under a high-power microscope a number of short, backward-project- 

 ing spines may be seen on the upper surface of the body. 



The sarcoptic mites penetrate the upper layer of the skin and exca- 

 vate burrows or galleries in which the mating of the sexes occurs and 

 the eggs are laid. Each female may lay from 10 to 25 eggs during the 

 egg-la}ung period, which probably lasts from 12 to 15 days. When 

 that period is completed the female dies in her burrow. The entire 

 life cycle is passed on the body of the host animal. The eggs hatch 

 in from 3 to 10 days, and the young mites after passing through 

 several molts reach maturity and begin laying eggs in 10 or 12 days. 



