Chapter 29

PARASITIC INSECTS AND MITES

Parasitic insects are common causes of skin diseases in domestic animals. The diseased conditions of the skin, and the irritation that they may cause the animal, depend on the life history and habits of the parasite. Species that are unable to live independently of a host and are permanent parasites are usually the most injurious to the animal. This is especially true of parasites that are capable of puncturing the skin or burrowing into it. Temporary parasites may cause fatal forms of disease. This is true of the larva? of the sheep bot-fly, which develop in the sinuses of the head, causing severe inflammation of these parts, nervous symptoms and death. The character of the symptoms of a parasitic disease depends on the habits of the parasite, and the tissue or organ, that it may attack.

The parasitic flies belong to the order _Diptera_, and the families _Muscidae_ and _OEstridae_. Fleas belong to the sub-order _Pulicidae_. The order _Hemiptera_ includes the lice, and the most important families are _Pediculidae_ and _Ricinidae_. Mites and ticks belong to the order _Acarina_. The most important parasites belonging to this order are the _Sarcoptidae_ and _Ixodidae_.

OESTRIDAE.--The three common bot-flies are the _Gastrophilus equi_, _Hypoderma lineata_ and _OEstrus ovis_. These flies are important because of the parasitic habits of their larva. They inhabit the stomach and intestines of horses (Fig. 62); the subcutaneous tissue and skin of cattle; and the sinuses of the head and nasal cavities of sheep.

_The common bot-fly of the horse_ (_G. equi_) has a heavy, hairy body. Its color is brown, with dark and yellowish spots. The female fly can be seen during the warm weather, hovering around the horse, and darting toward the animal for the purpose of depositing the egg. The color of the egg is yellow, and it adheres firmly to the hair. It hatches in from two to four weeks, and the larva reaches the mouth through the animal licking the part. From the mouth, it passes to the stomach, where it attaches itself to the gastric mucous membrane (Fig. 62). Here it remains until fully developed, when it becomes detached and is passed out with the fasces. The third stage is passed in the ground. This takes place in the spring and early summer and lasts for several weeks, when it finally emerges a mature fly.

_The bot-fly of the ox_ (_H. lineata_) is dark in color and about the size of a honey-bee. On warm days, the female may be seen depositing eggs on the body of the animal, especially in the region of the heels. This seems to greatly annoy the animal, and it is not uncommon for cattle to become stampeded. The egg reaches the mouth through the animal licking the part. The saliva dissolves the shell of the egg and the larva is freed. It then migrates from the gullet, wanders about in the tissue until finally it may reach a point beneath the skin of the back. Here the larva matures and forms the well-known swelling or warble. In the spring of the year it works out through the skin. The next stage is spent in the ground. The pupa state lasts several weeks, when the mature fly issues forth.

_The bot-fly of sheep_ (_O. ovis_) resembles an overgrown house-fly. Its general color is brown, and it is apparently lazy, flying about very little. This bot-fly makes its appearance when the warm weather begins, and deposits live larvae in the nostrils of sheep. This act is greatly feared by the animals, as shown by their crowding together and holding the head down. The larva works up the nasal cavities and reaches the sinuses of the head, where it becomes attached to the lining mucous membrane. In the spring, when fully developed, it passes out through the nasal cavities and nostrils, drops to the ground, buries itself, and in from four to six weeks develops into the mature fly.

SYMPTOMS OF BOT-FLY DISEASES.--The larvae of the bot-fly of the horse do not cause characteristic symptoms of disease. Work horses that are groomed daily are not hosts for a large number of "bots," but young and old horses that are kept in a pasture or lot and seldom groomed may become unthrifty and "pot bellied," or show symptoms of indigestion.

Cattle suffer much pain from the development of the larva of the _H. lineata_. During the spring of the year, the pain resulting from the presence of the larvae beneath the skin and the penetration of the skin is manifested by excitement and running about. Besides the loss in milk and beef production, there is a heavy yearly loss from the damage to hides.

The parasitic life of the bot-fly of sheep results in a severe catarrhal inflammation of the mucous membrane lining the sinuses of the head, and a discharge of a heavy, pus-like material from the nostrils. The irritation produced by the larvae may be so serious at times as to result in nervous symptoms and death.

TREATMENT OF BOT-FLY DISEASES.--The treatment of the different bot-fly diseases is largely preventive. This consists in either the destruction of the eggs or the larvae.

The different methods of destroying the eggs of the bot-fly of the horse are clipping the hair from the part, scraping off the eggs with a sharp knife, or destroying them by washing the part infested with eggs with a two or three per cent water solution of carbolic acid. This should be practised every two weeks during the period when the female deposits the eggs.

Housing the cattle, or applying water solutions of certain preparations to the skin that may keep the female from depositing eggs, may be practised for the prevention of the ox-warble. The most practical method of ridding cattle of this pest is to destroy the larvae. This can be done by examining each animal and locating the swelling or warble and injecting a few drops of kerosene into the opening in the skin. A better method is to enlarge the opening in the skin with a sharp knife, squeeze out the grub and destroy it. This should be practised in late winter and early spring.

The application of pine tar to the nostrils of sheep is the most practical method of preventing "grub in the head." This should be practised every few days during the summer months. A very good preventive measure is plenty of shade for the flock. Valuable animals may be treated by trephining into the head sinus and removing the "grub."

LICE.--The sucking lice belong to the genus _Hoematopinus_, and the biting lice of mammals belong to the genus _Trichodectes_. Different species of sucking and biting lice occur on the different species of farm animals. Poultry act as hosts for many different species of biting lice belonging to the following genuses: _Lipiurus, Goniodes, Goniocotes_ and _Menopon_.

_The common sucking lice_ occurring on animals are the large-headed horse louse, _H. macrocephalus_; the long-nosed ox louse, _H. tenuirostris_; the large-bellied ox louse, _H. curysternus_; the _H. stenopses_ of sheep; _H. suis_ of swine; and the _H. piliferus_ of the dog.

The _common biting lice_ (Fig. 63) that are found on domestic animals are the _T. pilosus_ and _T. pubescens_ of solipeds, _T. scalaris_ of the ox, _T. spoerocephalus_ of sheep and goats, _T. latus_ and _T. subrostratus_ of the dog and cat. _Menopon palidum, Lipiurus variabilis_ and _Gonoides dissimilis_ are the common lice found on poultry.

SYMPTOMS OF LICE.--The symptoms of lousiness depend on the variety of lice present, the degree to which the animal is infested with them, its physical condition and the care that it receives. Lice multiply more rapidly and cause greater loss during the winter months than they do in the summer, when the animals are not housed and the opportunity for infection from the surroundings is not so great. The sucking louse (Fig. 64) is the most injurious and irritating. The irritation and loss of blood that the animal may suffer when badly infested by this parasite may result in marked unthriftiness. Young and old animals that are not well cared for suffer most. The biting louse may bite through the superficial layer of the skin, and cause the animal to bite and rub the part. This irritation to the skin prevents the animal from becoming rested, and after a time seriously interferes with its thriftiness.

_Horses and mules_ show a staring, dirty, rough coat. The mane and tail may become broken and matted. The animal rubs against the stall, fences and trees, and bites the skin in its efforts to relieve the irritation. On examining the coat, nits are found adhering to the hair (Fig. 65). We should examine the parts of the skin covered by the long hair for the sucking lice; and the withers, abdomen and limbs for the biting lice.

_The symptoms of lousiness in cattle_ are about the same as occur in horses. Licking and rubbing the skin are prominent symptoms in cattle, and the coat becomes dirty and rough. The licked part is matted and curled. The lice may be discovered by parting the hair along the back and rump.

_The biting louse of sheep_ causes the fleece to become matted and tufts of wool are pulled out. This is brought about by the sheep rubbing and nibbling the fleece, and the lice cutting through the wool. The loss due to the damage to the fleece is usually greater than that resulting from unthriftiness.

_The hog-louse_ is the largest specie known. As well as the largest, it is the most common of all lice found on domestic animals. The favorite points of attack are the under surface of the body, the neck and the inside of the thighs. The irritation and itching are severe, and the hog rubs and scratches the skin. Young hogs suffer most from this parasite, and their thriftiness is greatly interfered with.

The long-haired breeds of _dogs_ suffer more from lice than the short-haired breeds. The almost constant scratching and biting of the skin result in its becoming badly irritated and scabby. The symptoms differ little from irritation to the skin caused by fleas, but the presence of biting or sucking lice enables the person making the examination to determine the cause of the irritation.

Lice are the most common parasites of _poultry_. It is uncommon to meet with a flock of fowls that are not hosts for one or more of the many different varieties of bird lice. Restlessness, picking, scratching, flapping the wings, abandoning the nest and loss of condition are common symptoms. Young birds suffer most from lice. This is especially true of young chickens, death frequently resulting. Old fowls may show little inconvenience unless badly infested. The finding of the lice with the head imbedded in the skin or on the feathers enables the person making the examination to positively diagnose the case. The head, back, region of the vent and beneath the wings are the parts that should be carefully examined for lice.

TREATMENT OF LOUSINESS.--The preventive treatment is very important. This consists in carefully examining all animals or birds that have been purchased recently, and if found to harbor lice, excluding them from the herd or flock until after they have been properly treated.

It is impossible to rid animals of lice if the quarters are thoroughly cleaned and disinfected. This is necessary in order to destroy lice that have become scattered about by the lousy animals, and prevent the reinfection of the treated animals. The best method to use in cleaning the quarters is to remove all litter and manure from the stable or houses and their immediate surroundings. It should be burned, or hauled to a field or lot where other animals cannot come in contact with it for a few months. The walls, floors and partitions should be sprayed with a three per cent water solution of liquor cresolis compositus. Lime may be scattered about the buildings, yards and runs. The most satisfactory method of destroying lice on the bodies of animals is by washing or dipping in a water solution or mixture of some reliable disinfectant or oil.

_Running hogs through a dipping tank_ that contains a one or two per cent water solution of liquor cresolis compositus, or a coal tar disinfectant, or that has from three-fourths to one and one-half inches of oil on top of the water, is the most satisfactory method of destroying the hog louse. Because of the thinness of the hog's coat and the danger from irritating the skin when strong solutions of a disinfectant are used, most swine breeders prefer crude oil as a remedy for lousiness in hogs. Crude oil may be applied to the bodies of hogs with a swab. If this method is practised instead of dipping, it is advisable to crowd the hogs into a small pen, and apply the oil in front and between the thighs and back of the arms. This may be practised during the cold weather when it is impossible to dip the animals.

_Horses_ may be washed with a one or two per cent water solution of liquor cresolis compositus, or a coal tar disinfectant. If the weather is cold, it is advisable to pick a sunny day, and blanket the animal after rubbing it as dry as possible in order to prevent chilling and catching cold.

_Cattle_ may be treated in the same manner as horses. Mercurial ointment rubbed in small amounts on the skin back of the horns and ears, where the animal cannot lick it, is a common remedy. The absorption of a small amount of this drug does the animal no harm, but a larger quantity may salivate it.

_Sheep_ are treated by dipping in a water solution of a reliable coal tar disinfectant. This should not be practised during cold weather, as the fleece does not dry out. Insect powder may be dusted into the fleece when it is impossible to dip the animal.

A very satisfactory treatment for lousiness in _dogs_ and _cats_ is to wash them with carbolized soap. We should wait a few minutes before rinsing off the soapy lather and drying the coat.

A number of different remedies are used for the treatment of lousiness in _poultry_. Dust baths and insect powder are recommended. Ointments are commonly used. One part sulfur and four parts vaseline, or lard, may be made into an ointment and applied to the head, neck, under the wings and around the vent. Mercurial ointment may be applied to the margin of the vent. Neither of them should be used for destroying lice on young chicks. Mercurial ointment should be used very carefully because of its poisonous effect. Lard may be used for destroying lice on young chicks. Crude petroleum may be sprayed among the feathers by a hand-sprayer, while the fowls are suspended by the feet.

None of the disinfectants and oils recommended for dipping and washing lousy animals destroy the nits. This makes it necessary to re-treat the animal in from eight to ten days after the first treatment.

THE SHEEP-TICK.--This is not a true tick. It resembles a fly more than it does a tick, and its right name is _Melophagus ovinus_ (Fig. 66). Louse-fly is a better name for this parasite than tick, as its entire life is spent on the body of a sheep. The general color of the body is brown. The legs are stout, covered with hair and armed with hooks at their extremities. The mouth parts consist of a tubular, toothed proboscis with which the parasite punctures the skin and sucks the blood. Within a few hours after birth, the larvae develop into pupae, which are hard, dark brown in color and firmly glued to the wool. The young louse-fly emerges from the pupa in from three to four weeks.

The sheep-tick is a very common external parasite. The adult parasites and the pupae are large and easily found. When badly infested with ticks, a sheep will rub, dig and scratch the skin and fleece. This results in pieces of wool becoming pulled out and the fleece appears ragged. After clipping the ticks migrate from the ewes to the lambs, which may become unthrifty and weak.

_The treatment_ consists in dipping the flock in a one or two per cent water solution of a coal-tar dip. Dips containing arsenic are most effective in ridding sheep of ticks.

SCABIES.--This parasitic disease is one of the oldest and most prevalent diseases of the skin. It is commonly known as scab or mange. The animals most commonly affected are sheep, horses and cattle.

_The disease is caused_ by _small mites_ or _acari_ that are naturally divided into the _Sarcoptes_, which burrow under the epidermis, forming galleries; the _Psoroptes_, which live on the surface of the skin where they are sheltered by scabs and scurf; and the _Symbiotes_, which also live on the surface of the skin, but prefer the regions of the hind feet and legs.

Acari multiply rapidly and live their entire life on the body of the host. A new generation is produced in about fifteen days. Gerlach has estimated the natural increase in three months at 1,000,000 females and 500,000 males. Scab and mange are exceedingly contagious diseases.

_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.

_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.