Part 23

2. Blood-sucking mange-mites living on the outer surface (Dermatocoptes);

3. Mange-mites which merely devour scales of the epidermis (Dermatophagus).

FIG. 125.—Mange Mite of the Pig (Sarcoptes scabiei, var. suis), seen from the ventral side. ]

It is obvious that sarcoptic scabies is not so easily cured in the same host as the dermatocoptic scabies, since the mites causing the former dig their passages into the epidermis, while those causing the latter at least remain on the surface. Dermatophagic scabies is most easily got rid of, since the mites which cause it not only remain on the outer surface of the skin, but also, instead of holding fast, run about here and there; it is easily understood that this kind of mange can often be removed by simple brushing.

FIG. 126.—Mange Mite of the Pig (Sarcoptes scabiei, var. suis), seen from the dorsal surface. × 200. ]

The itch, or mange (scabies), is caused by the irritation which the mites continually exert on the skin. The warmer the surroundings of the host, the more active the mites, and the more painful the skin disease. (The scarcoptes mites, e.g., are most unendurable in man when in bed, and scabby sheep are most tormented when in a warm fold.) The mites multiply with such enormous rapidity that it is easy to understand how a single fertilized female, transferred to a new host by contact with an affected animal, is able, in a short time, to make large patches of the skin mangy. The course of the disease is generally as follows:—Soon after infection small swellings appear, which become little bladders of the size of a pin’s head. These burst, and the affected parts of the skin are quickly covered with a crust formed from shrivelled bits of skin and dried-up fluid. In many places the attacked parts of the skin are moist, for the host, in consequence of the severe itching, rubs or knocks itself. In consequence of the shedding of fluid the hairs stick together, and later on fall out. The skin thickens, becomes encrusted, and is thrown into folds, between which there are deep cracks. Among domesticated animals the sheep is certainly the one which suffers most from scabies (Dermatocoptes), especially as the disease spreads rapidly in the warm sheltering fleece, which also makes the removal of the parasites a matter of the greatest difficulty. The wool gets dry and brittle in the diseased parts, and its fibres become loose, though they remain attached for a short time, since their tips are glued together by the sticky substance which exudes from the little thickenings in the skin. They gradually fall out, however, leaving the skin covered with a thick brownish crust, looking as if it were soaked with oil. Badly infested sheep get thin and even die. This, however, is not usually the case, and the injury consists in the great deterioration of the wool, both as regards quantity and quality.

The following summarizes the kinds of scabies affecting man and domestic animals, and indicates how far one kind of host can affect another:—

Itch of =Man= (Sarcoptes) can be caught by the dog, but by no other domestic animal.

Scabies of the =Horse=.—The sarcoptes mange of this animal is contagious for man, and for the ox, but no other domestic animal. The dermatocoptes mange (found more particularly on the inner sides of the legs, and on the genital organs, tail, and mane) does not spread to man or to other domestic animals. Nor is this the case with the dermatophagus mange of the horse (on the fetlocks and adjacent parts of the legs).

Scabies of the =Ox=.—The dermatocoptes mange of the ox (chiefly affecting the sides of the neck and root of the tail) spreads to men and horses, but not to sheep. The dermatophagus mange (principally on the root of the tail and near the anus) does not seem to be transmitted to man, horse, pig, or dog.

Scabies of the =Sheep=.—The dermatocoptes mange of sheep is not transmitted as a permanent disease to man, nor to other domestic animals (with the exception of the goat). The sarcoptes mange of the sheep (chiefly on the head) causes the itch in man.

Scabies of the =Pig= (Sarcoptes) is contagious for the dog, and causes an eruption in man.

Scabies of the =Dog= (Sarcoptes) can be caught by man, pig, and horse.

Scabies of the =Cat= (Sarcoptes) is contagious for man, horse, ox, dog, and rabbit.

Scabies of the =Rabbit= (Sarcoptes) is contagious for man, but this is not so with the dermatocoptes mange, which flourishes in the external passage of the ear in the rabbit.

Scabies of the =Fowl= (Sarcoptes), which affects the legs of hens, causing thickening of the skin and formation of large spongy crusts, may infect horses. Hen-houses should not be built in stables.

Remedies.—From the foregoing facts relating to the transmission of scabies from one host to another, the preventive measures at once follow: A mangy animal must not be allowed to come into contact either with another animal of the same kind or with an animal of any other kind for which the disease in question is contagious. If scabies appears in a few members of a flock or herd, it is absolutely necessary to separate the healthy animals from the sick ones,—and it is further necessary to cleanse and disinfect places where mangy animals have been kept, as well as implements or machines which they have touched, before sound animals are brought near such things. Cleansing of folds, etc., with hot water, followed by six weeks’ disuse. Cleansing of infected implements with hot soda and water. The first important thing to ascertain is whether a sick animal, which has the external symptoms of scabies, is really affected; in order to determine this the mange-mites must be found. If the mites cannot be found on the suspected animal, it must be brought into a warm stall and covered over; especial care must be taken to warm the places where the skin seems worst attacked; warmth makes the mites more active, and induces them to come to the surface. Sarcoptic mites are the worst. I will deal but briefly with the treatment of mangy animals, as it is usually best to obtain the advice of a veterinary surgeon. External applications must naturally be employed. It appears from the investigations of Vogel that corrosive sublimate and arsenic kill the mange-mites less rapidly and therefore less surely than creosote, carbolic acid, benzine, tar, caustic potash, and tobacco, or even soft soap. Zürn recommends a thorough smearing of soft soap on the parts affected. The soap is allowed to remain for some time, even for a whole day, the infested spots are then rubbed with hot water, and brushed, if possible, until the crust on the skin disappears. Other remedies may now be employed. As such, Zürn mentions creosote, diluted with spirit or oil (1 : 25). Also, among other things, the following are recommended—benzine shaken up with water (1 : 5–10), or a solution of 1 part caustic potash in 30 to 40 parts of water. The above and several other remedies can be used with good results in combating scabies in most of our domestic animals. But there is more difficulty with sheep than with other animals, for the fleece is a hindrance to the beneficial action of the wash employed. It is not possible to make the sheep quite healthy so long as they remain unshorn. Till then, the efforts made must be directed to preventing the spread of the mange. This is managed in the following way. The crust is scraped from the parts attacked, after the loose wool which covers them has been removed. The mangy places are then rubbed with a decoction of tobacco leaves with carbolic acid (1 part carbolic acid to 15 parts spirit and 60 parts water), or with some other of the remedies named above. When the sheep are shorn, first dip them in a solution (2 parts soda, 1 part lime, and 50 parts water) by which the crust on the affected places is softened; twenty-four hours later dip in a solution which will kill the mites. A decoction of tobacco (1 part tobacco to 12 parts water) may be used for this purpose, using for each sheep about 1¾ pints of the fluid, to which has been added 6½ drams carbolic acid and 6½ drams alcohol. The first washing must be followed by a second, for the fluid destroys only the mites and not their eggs. As the young mites are hatched out in three to seven days, the dipping must be repeated seven days afterwards.

Family: =Ixodidæ= (Ticks).

FIG. 127.—The Dog Tick (Ixodes ricinus). ]

Ticks are generally rather larger than the mites of the preceding family. The skin is tough as leather. The front part of the body is covered by a hard shield above; the skin of the hinder part, though tough, is very extensible. The front end bears a sucking apparatus formed by the pointed jaws, and by its means the tick pierces the skin of man or animals and holds on fast. Ticks are chiefly found in sandy soil, among bushes and shrubs, or among herbs. As long as they remain on the ground they are tolerably small (⅒ inch) and very active. They creep up haulms and branches, and rest in a suitable spot till a mammal or bird passes, when they attach themselves to its hair or feathers by their legs, and bore into its skin with their sharp mouth-parts. Having thus fixed themselves, they suck the blood of their temporary host. The walls of their stomach and intestine are extremely elastic, so that the tick, which at first is only about one-tenth of an inch long and one-sixteenth of an inch broad, becomes as big as a pea, or even a garden bean. When the tick has sucked itself as full as possible, it withdraws its mouth-parts from the skin of its host for the time being, and lets itself fall to the ground, where it lies for many weeks without feeding. The small and feeble legs of the tick are not able to move the heavy, blood-filled body, and movements do not take place for some time, till the greater part of the imbibed blood has been digested and the tick has shrunk once more to its normal size. What has been said about the habits refers only to the female; the much smaller male never seems to pierce mammals, and its food is not known. In pairing, it is found attached to the under side of the female, remaining there several days, even when the female is fixed to the host. Egg-laying does not take place till the host is quitted. As ticks draw blood from their host their presence, in spite of the fact that they remain but a short time, is not a matter of indifference, especially if large numbers affix themselves to one animal. Sheep and cattle become thin if daily attacked in the meadows by many ticks. The piercing of the skin causes a stinging sensation, followed later on by itching of the parts to which the ticks are attached. The ticks which are fixed must never be seized and pulled out, for the mouth-parts are so deeply imbedded in the skin that it is impossible to remove them by force, and the attempt would only result in tearing the body from the mouth-parts. A better plan is to put a drop of oil or tobacco water, or, still better, benzine, on the tick, when it will loosen itself. We distinguish between the =Dog Tick= (Ixodes ricinus), the =Sheep Tick= (I. reduvius), and the =Ox Tick= (I. reticulatus), which, however, are not found exclusively on the animals after which they are named. The first, although found most commonly on the dog, attacks men who force their way through underwood (hunters), and in the same way fixes on sheep and oxen. The last two species are chiefly, but not exclusively, found on sheep and goats.

Family: =Gamasidæ= (Beetle Mites).

Beetle mites are temporary parasites on insects, reptiles, and birds. They have no eyes, but possess shear-like jaws, and tolerably long hairy legs. The =Beetle Louse= (Gamasus coleoptratorum) lives on dung beetles, sexton beetles, etc.

The =Fowl Mite= (Dermanyssus gallinæ) is the size of a sand grain, and blood-red or red-brown in colour. During the night it is found in large numbers on the fowls, but during the day hides on the perches, in the nests, and particularly in the chinks and crannies in the walls of the poultry-house, also in dung. It draws much blood from the fowls, and disturbs their sleep by producing a constant itching, the result being that they get very thin. Remedy: Whitewash the fowl-houses twice a year (autumn and spring) with hot lime to which 5 per cent. of carbolic acid has been added. The wooden parts should be scalded with boiling water before whitewashing.

Family: =Trombidiidæ= (Running Mites).

Body four-cornered or longish oval; legs tolerably long, hairy; jaws claw or needle-shaped; surface of the skin velvety; colour reddish or yellowish. They run about with great rapidity on the ground, tree trunks, leaves, etc. Most species feed on the juices which they suck from insects, or from other arachnids.

The =Plant Mite=, or =Red “Spider”= (Tetranychus telarius),

is ovoid, at most one-fiftieth of an inch long; reddish (also yellowish or brownish), with a dark spot on each shoulder. Plant mites are often found in considerable numbers during the summer, especially on the under sides of the leaves of low-growing plants; on garden beans, turnips, and hops; on several ornamental plants, grasses, and various weeds; on roses, limes, horse-chestnut trees, elms, willows, and fruit trees. In some exceptionally dry summers the mite increases to such an extent as to become a great pest. On the upper sides of the infested leaves there is to be seen, besides the adult and immature mites, a whitish, mealy substance, consisting of the cast skins and whitish eggs. Many of the mites run about here and there, but most of them remain fixed, and suck the sap. All are covered by a delicate web, which is formed by the animal. The attacked leaves become limp, shrivel up, die, and fall off. In dicotyledonous plants the withering generally commences in the axils of the veins. The infested plants often die off gradually, but death may also take place with great rapidity. Annuals are often killed by the attacks of the mite. The mites pass the winter in the ground, under fallen leaves, under the bark of trees, etc.

CLASS IV.: =CRUSTACEA= (CRUSTACEANS).