CONTAGIOUS PUSTULAR DERMATITIS IN THE HORSE. ACNE.
History. Cause: bacillus. Symptoms; incubation 6 to 15 days, skin tenderness, heat, swelling like peas, hazel nuts, vesicles, pustules, exudation, concretions among hairs, depilation, healing in 15 days. Leaves white spots with lighter hair. Extension by grooming: general eruption: subcutaneous swelling, sloughs, delayed healing. Lymphangitis. Diagnosis: from chaps and bruises, from horse pox, from impetiginous eczema, from urticaria, from farcy. Prevention, quarantine new horses, separate diseased, disinfect skins of the unaffected, disinfect stables and harness. Treatment: soapy wash: germicide lotions.
This has been largely described as an imported disease thus on the European continent it is the English variola, and in England the Canadian contagious pustular affection. Yet the first authentic account dates back to 1841–2 when Goux found it attacking an entire squadron of the French army in a fortnight. Axe described it in England in imported Canadian horses in 1877, and Weber observed it in the same year on the continent, where it was attributed to imported English horses. In 1883 it was noted by Schindelka, in 1884 Siedamgrotzky inoculated it from the horse on two rabbits and two Guinea pigs, and to horse and goat. The rodents developed a “malignant œdema” at the point of inoculation and died in six days. Grawitz and Dieckerhoff cultivated the bacillus on ox or horse serum and found it 2μ in length, dividing by segmentation into round or ovoid refractive spores, which may remain connected as diplococci or short chains and which color deeply in fuchsin. It grows most rapidly at a temperature of 37° C., growth ceases at 17° C., and it is destroyed in half an hour at 80° to 90° C. Preserved, dry, it remained virulent for four weeks and produced the characteristic eruption when rubbed on the skin of the horse, ox, dog, sheep or rabbit. It proved fatal to all rodents, including white mice. The microbe is found abundantly in the pus and crusts and is easily shown when these are treated with potash. It produces no putrid fermentation.
Symptoms. When inoculated it had an incubation of six to fifteen days followed in mild cases by swelling heat and tenderness of the skin with collection of the hair in erect tufts. Next day there are rounded elevations like peas or hazel nuts, discrete or confluent on the swollen patches. These nodules, at first firm and resistant soon become soft in the center, forming vesicles and finally pustules, which burst in five or six hours and exude an abundant liquid which concretes in a thick amber colored mass. The hairs in the center of the resulting raw surface are easily detached leaving bare spots the size of a dime, with often times a slough attached in the center. When this is finally eliminated the surface gradually cicatrices and recovery may be complete in fifteen days. The skin remains long dappled from the partial discoloration of the epidermis in the seat of the pustules. The malady is local and hyperthermia is rarely seen. The submaxillary and pharyngeal lymph glands are usually swollen and indurated, but this disappears speedily after the subsidence of the eruption.
In certain cases the extent of the primary eruption is greater from the first, or it extends through reinfection by combs, brushes and rubbers used in grooming or by friction by the harness, the affected skin is hot, painful, congested and thickened throughout its entire substance, the pustules are much more numerous, often confluent, and may even implicate the subcutaneous connective tissue. The crusts formed on the sores may acquire a breadth of 1 inch to 1½ inch. Considerable abscesses may be formed and the lymph glands communicating with the affected part are hot and swollen. Even after the opening and discharge of the abscess, the base of the sore remains indurated and indolent, and centres of softening and caseation may appear so that healing is delayed for one or two months or more. In such cases extensive cicatrices remain after recovery. Lymphangitis is a common accompaniment with even abscess of the lymphatic glands.
Diagnosis. From chafing and bruising by the harness, this is easily recognized by its appearing also on other parts than those covered by the harness, by the development of the characteristic pustules, by its following a regular cycle of eruption and subsidence covering a definite period of usually 15 days, and by the indisposition to maintain itself indefinitely under the friction of the harness.
From horsepox it is distinguished by the habitual avoidance of the common seats of election of that disease (heels, lips, nostrils, buccal and nasal mucosæ, lips of the vulva), by the absence of hyperthermia, and by the comparative absence of the remarkable amber-like concretions which characterize horsepox in the lower limb.
From impetiginous eczema it is diagnosed by its contagious and inoculable properties, by the absence of the early falling of the hair from the circumscribed rounded nodules, and by the absence or moderate character of the pruritus which is usually intense in the eczema.
The eruption of urticaria appears much more suddenly, shows no tendency to form vesicles nor pustules, is not inoculable, and subsides often as suddenly as it appeared when the irritant food materials have been expelled from the alimentary canal.
From acute farcy it is distinguished by the moderate degree of the implication of the lymph vessels and glands, by the white creamy nature of the contents of the pustules, as compared with the glairy, oily nature of the farcy discharge, by the absence of coincident nasal ulcers, submaxillary nodular swellings or other lesions of glanders, by its short course and tendency to spontaneous early recovery, and by the absence of reaction under the mallein test.
In all cases the known prevalence of the contagious pustular dermatitis in the locality, or the introduction of strange horses which exhibit sequelæ of the lesions will assist greatly in the diagnosis.
Prevention. If animals are introduced from an infected or unknown locality they should be kept apart from others for two weeks. In a stable where it has already appeared the diseased and healthy should be carefully separated and the skins of those as yet unaffected may be washed with a solution of mercuric chloride (1 ∶ 1000) or creolin (1 ∶ 100). The walls of the stable should be whitewashed, and all stable utensils disinfected in boiling water or one of the above named antiseptics. The harness demands particular attention.
Treatment. This is essentially germicide. After a soapy wash, any one of the usual disinfectants may be used: aluminum acetate, (1 ∶ 15), mercuric chloride (1 ∶ 1000), carbolic acid (1 ∶ 50), creolin (1 ∶ 50), copper sulphate (1 ∶ 50), etc. Lead acetate 2 parts, alum 1 part and water 50 parts, has been found to be effective.