2. Blood-sucking mange-mites living on the outer surface
(_Dermatocoptes_);
3. Mange-mites which merely devour scales of the epidermis
(_Dermatophagus_).
[Illustration:
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.
[Illustration:
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_).
[Illustration:
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.