Causes. The disease is especially characteristic of animals in which the skin is naturally fine, thin and dry and covered sparsely with hair. It is therefore more common in the Arabian, Barb, English racer, American trotter and other breeds of a nervous organization than in the heavier draught breeds. Old horses in which the skin is drier and the hair thinner are more subject to it than the young. Again it has been especially noticed in the heats of summer with thin coat and a withering action of radiant heat on the skin, and less frequently in winter when the blood is driven from the surface by cold. Much also depends at times on the lack of grooming, on the accumulation of dust and dried up secretions about the roots of the hair, and on washing with caustic irritant soaps especially in long-haired regions. It has even been claimed that the ingestion of salt, potassium iodide, or bromide, etc., contributes to the affection. There is undoubtedly a certain individual predisposition to the disease, shown as already stated in certain breeds, but also inherent in particular families and even animals, and associated not only with the character of the skin, but also probably with variations in the activities and products of various internal organs. In man pityriasis versicolor is associated with a specific fungus, and in the horse Megnin has described cases in which the surface of the skin and especially the hair follicles show a mass of epidermic cells mingled with mycelium and an abundance of spores.
Symptoms. The scurfy product and depilation may be found in patches scattered indiscriminately over the body (generalized), or confined to particular regions (circumscribed) as to the head, ear, crest, tail, or the parts that receive the friction of the harness. It may commence as a dry, rigid, state of the skin under the headstall with loss of hair and the excess of dandruff. From this or from another point the extension takes place slowly and with comparatively little irritation or itching. The hair is pulled out with great ease, and from its spontaneous evulsion, more or less baldness appears progressing slowly from the original centres of the disease. It may leave the whole crest divested of the mane, or the tail of its hairs (rat tail), or the ears may become bare and scurfy. Again the parts subject to friction like the back of the ears, the crest, in front of the shoulder, or the seat of the saddle may be the main seats of depilation and baldness.
It is to be distinguished from dry eczema mainly by its tendency to spread over a larger area in place of confining itself to circumscribed patches, and more particularly by the absence of the marked thickness and rigidity of the skin which characterize eczema. From acariasis it is distinguished by the lack of the intense itching, of the tendency to more or less moist exudation and above all by the absence of the acari.
Treatment. It is well to correct any disorder of any of the internal organs, notably of the stomach, liver or kidneys, and to encourage a free circulation in and secretion from the skin. To fill the latter indication green food, ensilage, roots, sloppy mashes of bran, oilcake and the like may be given. Also bicarbonates of soda or potash or other alkaline diuretics, and in certain obstinate cases a course of arsenic. The alkalies tend to eliminate offensive and irritant matters and to lessen the irritation in the skin. A course of tonics is often valuable.
Locally Cadeac recommends potash soaps rubbed well into the affected parts. If this should fail some of the stimulant ointments as of tar, oil of tar, oil of white birch, oil of cade, creoline, creosote, lysol, naphthalin, may be tried. Megnin strongly recommends a combination of ointment of biniodide of mercury, 1 part, to mercurial ointment 3 parts. Others advocate salicylic acid (10 to 20%) mixed with Lassar paste which is compounded of 1 part each of zinc oxide and starch in 4 parts vaseline.
PITYRIASIS IN CATTLE.
On neck and dewlap; Causes: anæmia, debility, spoiled food, starvation, constitutional predisposition. Symptoms: shedding hair and scales without skin thickening, or itching. Treatment: green soap, tar, creolin, lysol, naphthalin, etc. Alkaline lotions: generally nutritive, succulent food, bitters, iron, arsenic, etc.
This is noticed especially on the neck and dewlap in connection with anæmia, low condition, unsuitable, innutritious and spoiled fodder and a constitutional predisposition. It has the same general characters as in the horse, an excessive production of dandruff or dry scales without any marked change in the thickness of the skin or in its circulation. Treatment consists in the application of green soap, pure or medicated, with tar, creolin, lysol, or other empyreumatic product. Lotions of carbonate or bicarbonate of potash are often effective. Any disorder of digestion, or of the urinary or hepatic functions, or of general nutrition should be corrected, and in most cases, a course of bitters, with iron and arsenic is desirable. A good, indoor hygiene or a run on succulent grass in the open air may be resorted to with benefit.
PITYRIASIS IN THE DOG AND CAT.
Head, neck and back of overfed, old house dogs. Symptoms: floury dandruff, with little itching or redness, on limited areas; in cats over the whole back, where stroking causes electric development, the collecting of the hair in tufts, and insufferable irritation. Hair constantly shedding without necessarily bare patches. Treatment: simpler, restricted diet, correct internal disorders, laxatives, arsenic, locally solutions of alkalies, borax, potassium sulphide, sulphur iodide, baths.