_Common sheep scab_ is caused by that specie of mites known as the _Psoroptes communis var. ovis_ (Fig. 67). Any part of the body may become affected. The bites of the mites greatly irritate the skin, and the animal scratches, bites and rubs the part in its effort to relieve the intense itching. The skin becomes inflamed and scabby, the wool is pulled and rubbed out, and the fleece becomes ragged (Fig. 68). By pulling wool out of the newly infested area, or collecting skin scrapings and placing this material on black paper in a sunny, warm place, the mites may be seen crawling over the paper. This method of diagnosis should be resorted to in all suspicious cases of skin disease, and before the disease has developed to any great extent.
The mite that most commonly causes _mange in cattle_ is the _Psoroptes communis var. bovis_. It may invade the skin in the different regions of the body, but it is in the regions of the tail and thighs that the first evidence of the mange is noticed. The animal rubs, scratches, and licks the part. The itching is intense. The hair over the part is lost and the skin appears inflamed, thickened, moist, or covered with white crusts. Cracks and sores may form in the skin. The examination of scrapings from the inflamed skin should be practised in order to confirm the diagnosis.
_Mange in horses_ may be caused by either psoroptic or sarcoptic mites.
_Psoroptes communis var. equi_ seems to be the more common parasite. The itching is intense. The inflamed areas are small at first and scattered over the regions of the rump, back and neck (Fig. 69). After a time the small areas come together and form large patches, and further spreading of the inflammation results from grooming, scratching and biting the skin.
Scattered, elevated eruptions on the skin from which the hair has dropped out are first noticed. These parts may show yellowish scabs. Later the skin is thickened, smooth, wrinkled, cracked, or covered with sores. Scrapings made from the inflamed areas of the skin may show the psoroptic mites.
_Mange in hogs_ is comparatively rare. It is caused by one of the sarcoptic mites. The thin portions of the skin are usually first invaded. There are violent itching and rubbing, and small, red elevations occur on the skin in the region of the ears, eyelids or inner surface of the thighs, depending on the part first invaded. The skin becomes greatly thickened and covered with crusts and scabs. Pus formation and ulceration may occur.
TREATMENT OF SCAB AND MANGE.--A careful inspection of recently purchased animals that pass through stockyards, or are shipped from sections where scab and mange are common skin diseases, is an important preventive measure. Infected animals should be completely isolated from the herd, and kept apart from other animals until after they have been treated. Hogs that are slightly infected should be quarantined and treated. If badly affected, they should be killed, and the carcass disposed of by burning or burying.
[Illustration: FIG. 69.--A severe case of mange.]
_The different remedies used_ in the treatment of the disease may be applied by dipping, hand dressing or washing, pouring, smearing and spotting. The first method is the most satisfactory. The last method may be used when a small area of the skin is involved, and during the cold weather. Washing or dipping the animal with a two per cent water solution of liquor cresolis compositus is an effective remedy for the psoroptic forms of scab and mange. Tobacco, lime and sulfur, and arsenical dips are recommended in the treatment of sheep and cattle. Ointments are recommended for animals that are slightly affected with mange. Lime and sulfur dips are recommended by the Bureau of Animal Industry. Small infected areas of the skin may be treated by applying sulfur-iodide ointment. The following ointment is commonly recommended: potassium sulfide ten parts, potassium carbonate two parts, and lard three hundred parts.
Sheep cannot be safely dipped for scab during the cold weather. If thickened and scabby, the skin should be scrubbed with the dip, or the animal prepared for dipping or washing by first clipping the hair or wool and scrubbing the skin with water and a good soap. In order to prevent reinfection, it is necessary to remove the animal to new quarters, or thoroughly clean and disinfect the old. It is necessary to wash or spray the fences, floors, walls, brushes and curry-combs with a disinfecting solution. Manure and other litter should be removed to a place where there is no danger from its distributing the infection.
DISEASES OF POULTRY CAUSED BY MITES.--Mites or acarina that cause diseases of poultry may live on the feathers, beneath the skin, and within the body of the fowl.
_The small, red mite (Dermanyssus gallinae)_ remains on the surface of the body only when feeding, and spends the rest of the time under collections of filth and in cracks in the roosts and walls of the house. This parasite causes the birds to become restless, emaciated and droopy.
_A very small mite (Sarcoptes mutans)_ is the cause of scaly leg. It lives under the skin. The joints of the feet appear affected, and the foot and leg become enlarged, roughened and scaly.
_Depluming scabies_ is caused by _Sarcoptes laevis var. gallinae_. This mite causes the feathers to break off at the surface of the skin. Masses of epidermic scales may form around the broken ends of the feathers. The diagnosis can be confirmed by examining the skin lesions and finding the mite.
_The air sac mite_ (_Cytodites nudus_) may cause sufficient irritation to the mucous membrane lining the air sacs to seriously obstruct the air passages with mucus, or produce death from exhaustion. A post-mortem examination of a fowl that has died of this disease shows the mites on the surface of the lining membrane of the air-sacs. They appear as a white or yellow dust.
TREATMENT OF POULTRY DISEASES CAUSED BY MITES.--Diseases of poultry caused by mites may be prevented by quarantining all recently purchased birds for a period of from two to four weeks, and by keeping the poultry houses clean. Birds that are found infested with parasites should be destroyed or returned. In case the bird is valuable and suffering from external parasites only, it should be given the necessary treatment.
_Red mites may be destroyed_ by thoroughly cleaning the poultry house, and spraying the roosts, nests, walls and floor with a three per cent water solution of liquor cresolis compositus. This should be repeated twice a week for two weeks.
_Scaly-leg may be treated_ by applying a penetrating oil to the feet and lower part of the leg. It is advisable to first remove the scales by scrubbing the part with soap and warm water. Dipping the feet in a mixture of kerosene one part and linseed oil two parts is recommended. This should be repeated as often as necessary.
QUESTIONS
1. Describe the different bot-flies.
2. Give the life history of the bot-fly of the horse; of the ox; of sheep.
3. Give the symptoms of bot-fly diseases.
4. Give the symptoms of lousiness.
5. Give treatment for lousiness of different farm animals.
6. What is the damage from the sheep-tick? Give treatment.
7. Describe the injury from scabies and mange.
8. Give treatments for these diseases.
9. Mention the several poultry mites and tell how to treat them.
CHAPTER XXV
ANIMAL PARASITES
The common parasitic diseases of domestic animals are caused by the following groups of worms: _Flukes_ or _trematoides_; _tapeworms_ or _Cestoides_; _thorn-headed worms_ or _Acanthocephales_; and _round-worms_ or _Nematoids_. Flat worms, such as tapeworms and flukes, require secondary hosts. The immature and mature forms of tapeworms are parasites of vertebrate animals, but an invertebrate host is necessary for the completion of the life cycle of the fluke. The hog is the only specie of domestic animals that becomes a host for the thorn-headed worm. The round-worm is a very common parasite. There are many species belonging to this class.
[Illustration: FIG. 70.--Liver flukes.]
DISTOMA HEPATICUM (COMMON LIVER FLUKE).--Sheep are the most common hosts for this parasite. It is present in the gall ducts and livers, and causes a disease of the liver known as liver rot. The liver fluke is flat or leaf-like and from thirteen to fifteen mm. long (Fig. 70). The head portion is conical. It has an oval and ventral sucker, and the body is covered with scaly spines. The eggs are oval and brownish in color.
_The life history_, in brief, is as follows: Each adult is capable of producing an immense number of eggs which are carried down the bile ducts with the bile to the intestine, and are passed off with the faeces. Under favorable conditions for incubation, such as warm, moist surroundings, the ova or eggs hatch and the _ciliated embryos_ become freed. The embryo next penetrates into the body of certain snails and encysts. The _sporocyst_, as it is now called, develops into a third generation known as _redia_ which escape from the cyst. The _daughter redia_ or _cercaria_, as they are now termed, leave the body of the snail and finally become encysted on the stems of grass, cresses and weeds. When taken into the digestive tract of the animal grazing over infested ground, the immature flukes are freed by the digestive juices. They then pass from the intestine into the bile ducts. The period of development varies from ten to twenty weeks; each sporocyst may give rise to from five to eight _redia_ and each redia to from twelve to twenty _cercaria_.
Fluke diseases occur among animals pastured on low, wet, undrained land.
Drying ponds and lakes are the homes of the fresh water snails, and in such places there are plenty of hosts for the immature flukes. Wet seasons favor the development of this parasite. Cattle and sheep that pasture on river bottom land in certain sections of the southern portion of the United States are frequently affected with fluke diseases.
_The symptoms of liver rot of sheep_ may be divided into two stages. The first stage is marked by increase in weight and improved condition. In the second stage of the disease, the animal shows a pale skin and mucous membrane, dropsical swellings, loss of flesh and weakness. The character of the symptoms of the disease depends on the age of the animals and the care that they receive. Young, poorly cared for animals suffer severely from the disease, and the death rate is usually heavy. The finding of fluke ova in the faeces is conclusive evidence of the nature of the disease. It may be advisable to kill one of the sick animals, and determine the nature of the disease by a post-mortem examination.
[Illustration: FIG. 71.--Tapeworm larvae in liver (_Echinococcus polymorphus_).]
[Illustration: FIG. 72.--Tapeworms.]
_The treatment is preventive_. Drainage water from a pasture infested with snails harboring immature flukes is a source of infection, and should not be used as a water supply for cattle and sheep. In sections where the disease is prevalent, sheep should not be pastured on low, poorly-drained land. Such land should be used for pasturing horses and cattle, but if possible, it should be first drained and cultivated. Careful feeding and good care may help the affected animals to recover.
[Illustration: FIG. 73.--Tapeworm larvae in the peritoneum (_Cysticercus cellulosa_).]
TAPEWORMS OR CESTOIDES.--Tapeworms are formed by a chain of segments, joined together at their ends, and are flat or ribbon-shaped (Fig. 71). The head segment is small, and possesses either hooks or suckers. It is by these that the worm attaches itself to the lining membrane of the intestine. The anterior segments are smaller and less mature than the posterior segments. Each segment is sexually complete, possessing both the male and female organs, and when mature, one or more of them break off and are passed out with the faeces. The mature or ripe segments are filled with ova. On reaching the digestive tract of a proper host, usually with the drinking water or fodder, the embryo is freed from the egg. The _armed embryo_ uses its hooklets in boring its way through the wall of the intestine. It then wanders through the tissues of its host until it finally reaches a suitable place for development (Figs. 71 and 73). On coming to rest, it develops into the larva or bladder-worm, which when eaten by a proper host gives rise to the mature tapeworm.
The following tables give the most important tapeworms:
ADULT FORMS
Name Host Organ
Taenia expansa Sheep and ox Intestine Taenia fimbriata Sheep Liver Taenia denticulata Cattle Intestine Taenia alba Cattle Intestine Taenia perfoliata Solipeds Intestine Taenia mamillana Solipeds Intestine Taenia echinococcus Dog Intestine
LARVAL FORMS
Name Host
Cysticercus bovis Cattle Cysticercus cellulosa Swine and man Cysticercus tennicollis Cattle, sheep and swine Coenurus cerebralis Cattle and sheep Echinococcus polymorphus Cattle, sheep, swine and man