Mange and Lice of Horses and Mules 555 Sick animals should be isolated in Good nursing practices, such as re- screened quarters and sprayed at in- peated grooming, turning prostrate tervals to limit opportunities for blood- animals from side to side every hour sucking to get to them. or so, and protection from the elements Transmission by insects from ani- and self-injury are helpful. mals dead of the disease is unlikely, Antiencephalitis vaccines have been but it is wise nevertheless to bury such developed for protection of man. They cadavers and disinfect quarters the have been used in laboratories to pre- sick animals used before they died. vent accidental infections. Under A specific antiencephalomyelitis se- proper conditions—which should be rum is commercially available. If such determined only by public health or serum is administered in time to ani- laboratory officials—they may be ap- mals in afifected stables, some may be plicable in epidemics. protected. Effectiveness of the serum is limited, however, both as to degree M. S. SHAH AN in i^jj became director and to duration. The preventive effect of the Plum Island Animal Disease Labora- of the serum diminishes to practically tory of the Department of Agriculture. nothing within 2 or 3 weeks. H. W. ScHOENiNG was graduated from Injections of fluids intravenously, the School of Veterinary Medicine^ Uni- rectally, or by stomach tube are con- versity of Pennsylvania^ in igoy^ and served sidered advantageous in combating in the Department from igoy to igjj, except extreme dehydration. during a period of military service.

Mange and Lice of Horses and Mules

F. D. ENZIE

MANGE, barn itch, scab, , and on currycombs, brushes, blankets, and itch are general terms applied to a other equipment. group of contagious skin diseases Ordinarily the disease spreads fastest caused by minute, insectlike parasites in winter when the animals may be called . Horses and mules may be closely confined or crowded together. affected with three different types of In the warmer seasons, when the these pests. Sarcoptes, Psoroptes, and animals are on pasture or are other- Chorioptes. The diseases they produce wise exposed to sunlight, the disease are known as sarcoptic, psoroptic, and tends to disappear or lie dormant. It chorioptic mange, respectively. becomes active again under conditions The mites spend their entire life of winter management. cycles in or on the skin of the host Sarcoptic mange is the type most animal. Each type of , as it commonly found among horses and carries on the various processes of life, mules in the United States. The mite produces lesions—injuries—that are equi causes it. The more or less characteristic. mature female is about one-fiftieth of The three kinds of mange usually an inch long. The male is a little are transmitted by direct contact be- smaller. They are just visible to the tween healthy and infected animals, unaided eye. although the mites may be transferred These white or yellowish parasites 556 Yearbook of Agriculture 1956 are round or slightly oval, like a horse- The first lesions generally occur on shoe. They have four pairs of short, the head, neck, and shoulders, but thick legs. Only the first two pairs of they may start on any part of the body. legs, on either side of the bluntly From the primary injuries, the disease rounded head, extend beyond the spreads to other parts of the skin margin of the body. surface. Furthered by the animal's The sarcoptic mites burrow in the scratching and rubbing, the lesions upper layer of the skin and form may extend over much of the body tunnels, in which they mate and lay within a few weeks, particularly if the eggs. Each female may deposit 25 eggs animal's general resistance is low on in about 2 weeks. The young mites account of a heavy burden of internal that develop from the eggs mature in parasites or a poor nutritional state. 14 or 15 days. A new generation of Sarcoptic mange is contagious to mites therefore is produced about horses of all ages and classes. It also is every 2 weeks, a factor of importance transmissible from one class of live- in determining the intervals between stock to another and from animals to treatments with medicinal agents. people. It is tremendously important The mites cannot complete their life therefore to have an accurate, early cycle off the host, but the adults may diagnosis, to isolate aff'ected animals survive for a month or more if temper- from all other livestock, and to under- ature and moisture are suitable. take treatment and other control The burrows extend to the deep, measures promptly. sensitive layers of the skin. There the To diagnose sarcoptic mange pos- activities of the mites cause intense itively, one has to find the mite. That irritation and itching. The horse seeks is done by microscopic examination of relief by rubbing the affected places skin scrapings from the edge of fresh, against any available object and other active lesions. Because the mites live in animals. Blisters and small lumps or burrows in the skin, deep scrapings ridges develop. The skin becomes must be made in order to find them, swollen and inflamed. The constant often to the point of drawing blood. In rubbing causes the vesicles, or blisters, the advanced stages of the disease, to rupture and discharge serum. The when the skin has become dry and serum, mixed with scurf and other leathery, the mites are hard to find. foreign matter, becomes dry and forms scabs. Bacterial infections occa- PSOROPTIG MANGE MITES, Psowptes sionally become established under the equi equi, are oval and somewhat larger scabs and make the condition worse. than those that produce common scab The mites constantly move from the in horses and mules. The male and edges of the lesions to the surrounding female are one-fiftieth and one-fortieth healthy skin, and so the condition of an inch long, respectively. Against a spreads over the body. The lesions may black background they are visible progress rapidly or slowly, depending without magnification. The elongate, on the animal's general physical con- tapering head and the four pairs of dition and the amount of care and legs extend well beyond the margin of attention it receives. the body. As the disease advances, the areas The psoroptic mites do not form first afi'ected become dry, rough, and burrow^s in the skin but live in colonies bare. The skin in the final stages is on the surface. They pass their entire greatly thickened, wrinkled, and leath- life cycle on the host. A female may lay ery. The mites are inactive then and 15 to 25 eggs. The young mites, which hard to find, but the skin remains hatch in about 4 days, reach the egg- leathery. The skin may continue to be laying stage ID to 12 days later. Psorop- unpliable for some time after the mites tic mites may live a year or more in are destroyed. barns or sheds, but probably they Mange and Lice of Horses and Mules 557 cannot survive more than a fev^ weeks respects. They have the same general when exposed to the sun. conformation, live on the surface of the The first lesions of psoroptic mange skin, and produce similar (though gen- generally appear on the poll, under the erally less extensive) lesions. mane, or at the base of the tail, but These mites usually attack the lower they may start on any part of the body part of the legs and generally remain that is thickly covered with hair. Itch- below the hocks and knees. The con- ing is intense. dition therefore is commonly called Serum accumulates in the hair from foot mange. ruptured vesicles and papules, be- The lesions occur oftenest on the comes mixed with foreign matter, and hind legs and are like those of the dries to form crusts and scabs. Irrita- psoroptic mange in most ways. Infect- tion of the lesions is increased by the ed animals exhibit the same general bacterial infections that often become restlessness and irritation as in other established under the scabs. The mites types of mange and attempt to allay constantly move toward the healthy the itching by pawing, rubbing, lick- skin near the edges of the wound. ing, or biting the affected parts. Some mites migrate to other areas where they may start new lesions. The PREVENTION of infestation with itching continues, and the skin be- mange mites and other external para- comes mutilated from the constant sites is largely a matter of employing rubbing and biting. The skin over good husbandry practices. large areas of the body finally becomes Clean quarters, regular grooming, thickened, wrinkled, bare of all hair, and a balanced diet are important in and covered with thick and adherent maintaining and promoting general scabs. health and preventing the develop- Psoroptic mites are more host specific ment and spread of all parasitic skin than those that produce common diseases. Blankets, saddles, and har- mange. The variety that afí'ects horses nesses should be cleaned and disin- and mules is not transmissible to man fected regularly. Currycombs and or to other livestock. Among horses, brushes should be cleaned thoroughly however, psoroptic mange is more immediately after use. highly contagious and spreads faster Mange in horses and mules can be than sarcoptic mange. Infections usu- eradicated by dipping or spraying ally are acquired by contact with with suitable chemical agents. infected animals, but indirect transfer Dipping is preferable because it as- of mites may occur from equipment or sures thorough coverage of the ani- contaminated stalls and sheds. mal—to be effective, the medicament The diagnosis of psoroptic mange is must be brought into direct contact established by identifying the charac- with the parasites. All horses on the teristic mite obtained from skin scrap- premises should be treated whether or ings. As these mites live on the surface not a specific diagnosis is established of the skin, comparatively superficial in each animal. scrapings usually are enough. In the Two dippings 10 to 12 days apart early stages of the disease, the mites ordinarily will be enough to cure pso- generally are most plentiful around roptic and chorioptic mange. the edges of fresh wounds. After the Three or more treatments may be condition is well established, the mites necessary for sarcoptic mange because may be found also near the edges of of the location of the mites in burrows scabs or in the furrows between folds in the skin. of skin. Animals that have chorioptic mange may be driven through a shallow wad- THE CHORIOPTIG MITES, Chorioptes equi^ ing tank if the lesions are confined to resemble the psoroptic mites in many the lower parts of the legs. 558 Yearbook of Agriculture 1956 Dipping is not feasible during severe than a week, although some may sur- winter weather. It is impractical when vive as long as i o days if kept on tufts only a few animals are involved. of hair. The sucking lice cannot survive Spraying is a useful alternative method. more than 2 or 3 days away from the It is effective if the entire body surface host animal. is completely wetted. Sucking lice mostly prefer the head, With either method, advanced le- neck, back, and inner surface of the sions that are covered with hard scabs thighs, but they move about on the or crusts should be thoroughly soaked skin and hair when they are not feed- and softened by hand with warm dip ing. They get nourishment by piercing or spray before treatment. the skin and sucking blood and fluids. Besides rotenone and the standard Biting lice may be found anywhere lime- and nicotine dips, several on the body, although they seem to newer treatments are used against the occur in largest numbers around the three kinds of mange affecting horses withers and base of the tail. They do and mules. They include lindane, ben- not suck blood but feed on hair, scales, zene hexachloride, benzyl benzoate, and exudations from the skin. and tetraethylthiuram monosulfide. The commonest method of trans- mission is by direct contact between Tw^o KINDS OF LICE, a bloodsucking clean and infested animals. species called Haematopinus asini and Hair and scurf from grooming equip- a biting known as Bovicola equi, ment and hair clipped from infested infest our horses and mules. horses should be collected promptly The sucking lice are the more injuri- and burned. The ground or floor on ous, because heavy infestations mean a which the clippings accumulated heavy loss of blood that seriously weak- should be thoroughly sprayed with an ens the animal. effective insecticide, such as DDT, Lice occur in largest numbers in lindane, or methoxychlor. Infested winter, when the hair is long and the stables and yards should be cleaned animals generally are closely confined. thoroughly by removing accumula- The sucking lice are easily told from tions of litter and manure. The stables biting lice by their larger size, pointed should be sprayed also with insecticide. heads, and bluish bodies. Mature Treatment of infested animals may adults are about a third as broad as be by dipping, spraying, w^ashing, or long, and the overall length is about dusting with insecticidal preparations. one-eighth inch. The best method in any particular The much smaller biting lice have a case depends on the number of horses white or yellowish body and a red or to be treated, prevailing weather con- brown head, which is short and blunt. ditions, and the available facilities. Sucking and biting lice pass their Dipping is most effective, because it entire lives on the host animal. They assures thorough coverage of the are generally transmitted by direct animal. It is preferred where winters contact between animals. are mild and a large number of The eggs, or nits, of the sucking animals is involved. louse usually are close to the skin and Methoxychlor, DDT, lindane, ben- attached firmly to the hairs. Most of zene hexachloride, chlordane, and the eggs hatch in about 2 weeks. The are effective against both young lice reach maturity about i2 sucking and biting lice. days later. The eggs of the biting louse are de- F. D. ENZIE has been concerned with posited in the same general manner, investigations oj parasite treatment since but have a shorter incubation period. ig42. He joined the Department of Agri- When they are removed from the culture in 1940, He is a parasitologist in host, most of the biting lice die in less the Agricultural Research Service.