THE MERCK VETERINARY MANUAL
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Mange in Horses

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Sarcoptes scabiei var equi is rare in the USA but is the most severe type of mange in horses. The first sign is intense pruritus due to hypersensitivity to mite products. Early lesions appear on the head, neck, and shoulders. Regions protected by long hair and lower parts of the extremities are usually not involved. Lesions start as small papules and vesicles that later develop into crusts. Alopecia and crusting spread, and the skin becomes lichenified, forming folds. If untreated, lesions may extend over the whole body, leading to emaciation, general weakness, and anorexia. Negative skin scrapings do not rule out the disease; biopsy may establish a diagnosis. If suspected, sarcoptic mange must be treated. Organophosphate insecticides or lime-sulfur solution can be used by spraying, sponging, or dipping. Treatment should be repeated at 12- to 14-day intervals at least 3–4 times. Alternatively, the oral administration of ivermectin or moxidectin at 200 μg/kg can be attempted. Several treatments are required 2–3 wk apart. It is important to treat all contact animals.

Psoroptes equi is rare in horses; it produces lesions on thickly haired regions of the body, such as under the forelock and mane, at the base of the tail, under the chin, between the hindlegs, and in the axillae. P cuniculi can sometimes cause otitis externa in horses and may cause head shaking. Pruritus is characteristic. Lesions start as papules and alopecia and develop into thick, hemorrhagic crusts. Mites are more easily recovered from skin scrapings compared with sarcoptic mange. Treatment is as for sarcoptic mange.

Chorioptic mange is common in heavy breeds of horses. Lesions caused by Chorioptes equi start as a pruritic dermatitis affecting the distal limbs around the foot and fetlock. Papules are seen first, followed by alopecia, crusting, and thickening of the skin. A moist dermatitis of the fetlock develops in chronic cases. It is a differential diagnosis for “greasy heel” in draft horses. The signs subside in summer but recur with the return of cold weather. The disease course is usually chronic without treatment, but the prognosis is favorable when treated. Topical treatments recomended for other manges are effective.

Demodex equi is rare in horses. The mites live in the hair follicles and sebaceous glands; D equi lives on the body, and D caballi in the eyelids and muzzle. Demodicosis in horses can manifest as patchy alopecia and scaling or as nodules. Lesions appear on the face, neck, shoulders, and forelimbs. Pruritus is absent. This disease has been reported in association with chronic corticosteroid treatment. No effective treatment regimens have been developed. Amitraz, used in other species, is contraindicated in horses because it can cause severe colic and death.

Trombiculid mites can parasitize the skin of horses, especially during the late summer and fall. The adult mites live on invertebrates and plants; the larvae normally feed on small rodents, but they can opportunistically feed on humans and domestic animals including horses. Lesions consist of severely pruritic papules and wheals. Specific treatment is not required; the pruritus can be controlled with glucocorticoids. Repellents may help prevent infestation.

These mites usually feed on organic material in straw and grain and can opportunistically infest the skin of horses. Papules and wheals appear on the face and neck if horses are fed from a hay rack, and on the muzzle and legs if fed from the ground. Pruritus is variable and can be controlled with glucocorticoids.

Last full review/revision July 2011 by Bertrand J. Losson, DVM, PhD, DEVPC; Bernard Mignon, DVM, PhD, DEVPC

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