Mange and Lice of Horses and Mules

F. D. ENZIE.

MANGE, barn itch, scab, scabies, and itch are general terms applied to a group of contagious skin diseases caused by minute, insectlike parasites called mites. Horses and mules may be affected with three different types of these pests, Sarcoptes, Psoroptes, and Chorioptes. The diseases they produce are known as sarcoptic, psoroptic, and chorioptic mange, respectively.

The mites spend their entire life cycles in or on the skin of the host animal. Each type of mite, as it carries on the various processes of life, produces lesions injuries that are more or less characteristic.

The three kinds of mange usually are transmitted by direct contact between healthy and infected animals, although the mites may be transferred on currycombs, brushes, blankets, and other equipment.

Ordinarily the disease spreads fastest in winter when the animals may be closely confined or crowded together.

In the warmer seasons, when the animals are on pasture or are otherwise exposed to sunlight, the disease tends to disappear or lie dormant. It becomes active again under conditions of winter management.

Sarcoptic mange is the type most commonly found among horses and mules in the United States. The mite Sarcoptes scabiei equi causes it. The mature female is about one-fiftieth of an inch long. The male is a little smaller. They are just visible to the unaided eye.

These white or yellowish parasites are round or slightly oval, like a horseshoe. They have four pairs of short, thick legs. Only the first two pairs of legs, on either side of the bluntly rounded head, extend beyond the margin of the body.

The sarcoptic mites burrow in the upper layer of the skin and form tunnels, in which they mate and lay eggs. Each female may deposit 25 eggs in about 2 weeks. The young mites that develop from the eggs mature in 14 or 15 days. A new generation of mites therefore is produced about every 2 weeks, a factor of importance in determining the intervals between treatments with medicinal agents.

The mites cannot complete their life cycle off the host, but the adults may survive for a month or more if temperature and moisture are suitable.

The burrows extend to the deep, sensitive layers of the skin. There the activities of the mites cause intense irritation and itching. The horse seeks relief by rubbing the affected places against any available object and other animals. Blisters and small lumps or ridges develop. The skin becomes swollen and inflamed. The constant rubbing causes the vesicles, or blisters, to rupture and discharge serum. The serum, mixed with scurf and other foreign matter, becomes dry and forms scabs. Bacterial infections occasionally become established under the scabs and make the condition worse.

The mites constantly move from the edges of the lesions to the surrounding healthy skin, and so the condition spreads over the body. The lesions may progress rapidly or slowly, depending on the animal's general physical condition and the amount of care and attention it receives.

As the disease advances, the areas first affected become dry, rough, and bare. The skin in the final stages is greatly thickened, wrinkled, and leathery. The mites are inactive then and hard to find, but the skin remains leathery. The skin may continue to be unpliable for some time after the mites are destroyed.

The first lesions generally occur on the head, neck, and shoulders, but they may start on any part of the body. From the primary injuries, the disease spreads to other parts of the skin surface. Furthered by the animal's scratching and rubbing, the lesions may extend over much of the body within a few weeks, particularly if the animal's general resistance is low on account of a heavy burden of internal parasites or a poor nutritional state.

sarcoptic mange is contagious to horses of all ages and classes. It also is transmissible from one class of livestock to another and from animals to people. It is tremendously important therefore to have an accurate, early diagnosis, to isolate affected animals from all other livestock, and to undertake treatment and other control measures promptly.

To diagnose sarcoptic mange positively, one has to find the mite. That is done by microscopic examination of skin scrapings from the edge of fresh, active lesions. Because the mites live in burrows in the skin, deep scrapings must be made in order to find them, often to the point of drawing blood. In the advanced stages of the disease, when the skin has become dry and leathery, the mites are hard to find.

PSOROPTIC MANGE MITES, Psoroptes equi equi, are oval and somewhat larger than those that produce common scab in horses and mules. The male and female are one-fiftieth and one-fortieth of an inch long, respectively. Against a black background they are visible without magnification. The elongate, tapering head and the four pairs of legs extend well beyond the margin of the body.

The psoroptic mites do not form burrows in the skin but live in colonies on the surface. They pass their entire life cycle on the host. A female may lay 15 to 25 eggs. The young mites, which hatch in about 4 days, reach the egg-laying stage 10 to 12 days later. Psoroptic mites may live a year or more in barns or sheds, but probably they cannot survive more than a few weeks when exposed to the sun.

The first lesions of psoroptic mange generally appear on the poll, under the mane, or at the base of the tail, but they may start on any part of the body that is thickly covered with hair. Itching is intense.

Serum accumulates in the hair from ruptured vesicles and papules, becomes mixed with foreign matter, and dries to form crusts and scabs. Irritation of the lesions is increased by the bacterial infections that often become established under the scabs. The mites constantly move toward the healthy skin near the edges of the wound.

Some mites migrate to other areas where they may start new lesions. The itching continues, and the skin becomes mutilated from the constant rubbing and biting. The skin over large areas of the body finally becomes thickened, wrinkled, bare of all hair, and covered with thick and adherent scabs.

Psoroptic mites are more host specific than those that produce common mange. The variety that affects horses and mules is not transmissible to man or to other livestock. Among horses, however, psoroptic mange is more highly contagious and spreads faster than sarcoptic mange. Infections usually are acquired by contact with infected animals, but indirect transfer of mites may occur from equipment or contaminated stalls and sheds.

The diagnosis of psoroptic mange is established by identifying the characteristic mite obtained from skin scrapings. As these mites live on the surface of the skin, comparatively superficial scrapings usually are enough. In the early stages of the disease, the mites generally are most plentiful around the edges of fresh wounds. After the condition is well established, the mites may be found also near the edges of scabs or in the furrows between folds of skin.

THE CHORIOPTIC MITES, Chorioptes equi, resemble the psoroptic mites in many respects. They have the same general conformation, live on the surface of the skin, and produce similar (though generally less extensive) lesions.

These mites usually attack the lower part of the legs and generally remain below the hocks and knees. The condition therefore is commonly called foot mange.

The lesions occur oftenest on the hind legs and are like those of the psoroptic mange in most ways. Infected animals exhibit the same general restlessness and irritation as in other types of mange and attempt to allay the itching by pawing, rubbing, licking, or biting the affected parts.

PREVENTION of infestation with mange mites and other external parasites is largely a matter of employing good husbandry practices.