Young animals frequently die of inflammation of the digestive tract. The immunity conferred by an attack of the disease is not permanent.

[Ill.u.s.tration: FIG. 107.--Slaughtering a herd of cattle affected with foot-and-mouth disease. (Photographed by S. J. Craig, County Agricultural Agent, Crown Point, Indiana.)]

The most economical measures of _prevention and control_ are to buy and slaughter all diseased and exposed animals, bury the carca.s.ses in quicklime, disinfect the premises (Figs. 107, 108 and 109) and enforce a district, county and State quarantine, until after the infection has died out. This statement may not hold true of methods of control in countries where foot-and-mouth disease is widely distributed.

TETa.n.u.s. LOCKJAW.--This is an acute infectious disease that is characterized by spasmodic contractions of voluntary muscles. The specific germ remains at the point of infection, and produces toxins that cause tetanic contractions of the muscles. It commonly affects horses, mules, cattle, sheep and swine. The disease is most common in warm, temperate climates.

[Ill.u.s.tration: FIG. 108.--Disinfecting boots and coats before leaving a farm where cattle have been inspected for foot-and-mouth disease.

(Photographed by S. J. Craig, County Agricultural Agent, Crown Point, Indiana.)]

[Ill.u.s.tration: FIG. 109.--Cleaning up and disinfecting premises where an outbreak of foot-and-mouth disease has occurred.]

The _specific cause_ is a pin-shaped germ, the _Bacillus tetani_ (Fig.

110), that is present in the soil, especially those that are rich and well manured. The germ enters the body by way of a wound, especially punctured wounds. Infection may take place through some wound in the mucous membrane lining the mouth, or other parts of the digestive tract. Infection may follow a surgical operation, such as castration. In any case, the germ requires an absence of air (oxygen) for its development.

_The period of incubation_ varies from one to two weeks, the length of time depending on the nearness of the wound to a large nerve trunk or brain.

[Ill.u.s.tration: FIG. 110.--_Bacillus tetani_.]

The first _symptom_ observed is a stiffness of the muscles, especially those nearest the point of inoculation or wound. The muscles of the head, neck, back and loins are often affected first, and when pressed upon with the fingers feel hard and rigid. The disease rapidly extends, producing spasms of other muscles of the body. In breathing, the ribs show less movement than normal, the head is held in one position and higher than usual, the ears are stiff or p.r.i.c.ked, the nostrils dilated, the lips rigid or drawn back and the eyes retracted, causing the "third eyelid" to protrude over a portion of the eye (Fig. 111). In most cases the muscles of mastication and swallowing are affected. The animal may be unable to open its mouth and swallows with difficulty. When standing, the limbs are spread out so as to increase the base of support, and in acute cases about to terminate fatally, the pulse is quick and small and the respiration shallow, rapid and labored. The animal sweats profusely, falls down and struggles violently, but remains conscious to the end.

[Ill.u.s.tration: FIG. 111.--Head of horse affected with teta.n.u.s, showing "third eyelid" protruding over the eye.]

In the _subacute form_ (Fig. 112) the symptoms are mild, and the animal may be able to move about, eat and drink without very great effort.

[Ill.u.s.tration: FIG. 112.--A subacute case of teta.n.u.s.]

_Treatment_ is largely preventive. All wounds should be carefully disinfected. This is especially advisable in punctured wounds of the foot.

In communities, or on premises where teta.n.u.s is a common disease, animals that have punctured or open wounds should be given a protective dose of teta.n.u.s ant.i.toxin.

_The curative treatment_ is largely good care. If a wound is present, it should be thoroughly disinfected. The animal may be supported by placing it in a sling. A comfortable box-stall, where the animal is not annoyed by noises or worried by other animals, is to be preferred. A fresh pail of water should be given the animal several times daily.

_The course_ of the disease varies. Death may occur within a few days, or the disease may last two or three weeks. Animals that recover from teta.n.u.s may show symptoms of the disease for several weeks. The death-rate is highest in hot climates and during the summer months.

If the animal can eat, it is not advisable to feed a heavy ration of roughage or grain. A very light diet of soft food, such as chops and bran-mash, prevents constipation and encourages recovery. Drugs that have a relaxing effect on the muscles may be given. Teta.n.u.s ant.i.toxin may be given in large doses.

QUESTIONS

1. What is septicaemia and pyaemia?

2. What is haemorrhagic septicaemia? Give methods of spreading and controlling this disease.

3. Give the cause of anthrax and symptoms.

4. What control measures are recommended in anthrax?

5. What is ulcerative sore mouth? Give the treatment.

6. Describe the symptoms occurring in rabies, and state the control measures recommended.

7. Name the species of animals affected by foot-and-mouth disease, and the countries where the disease is prevalent.

8. Give the methods of distribution and control of foot-and-mouth disease.

9. What is the specific cause and method of infection in teta.n.u.s? Give the treatment.

CHAPTER XXIX

INFECTIOUS DISEASES OF THE HORSE

STRANGLES. DISTEMPER.--This is an acute infectious disease a.s.sociated with a catarrhal condition of the air-pa.s.sages and suppuration of the lymphatic glands in the region of the throat. Colts are the most susceptible to the disease. One attack renders the animal immune against a second attack of the disease, but the immunity is not always permanent.

_The specific cause_, _Streptococcus equi_ (Fig. 113), was discovered by Schutz in 1888. Strangles is commonly spread by exposing susceptible animals to diseased animals, either by direct contact, or by exposing them to the infection in the stable and allowing them to drink or eat food from watering and feeding troughs on premises where the disease exists. The predisposing causes are cold and sudden changes in the weather. For this reason the disease is most prevalent during the late winter and early spring.

[Ill.u.s.tration: FIG. 113.--Streptococcus of strangles.]

_The period of incubation varies_, usually from four to eight days.

_The symptoms_ at the beginning of the attack are a feverish condition and partial loss of appet.i.te. The visible mucous membranes are red and dry.

This is followed by watery nasal secretions that become heavy and purulent within a few days. The inflammation may extend to the larynx and pharynx.

The glands in the region of the jaw become hot, swollen and painful, and the animal may be unable to eat or drink. The swelling and inflammation of the throat, and the heavy, pus-like secretions that acc.u.mulate in the nasal cavities, cause difficult respirations. After a few days the abscesses usually break, and the symptoms are less severe. If the abscesses break on the inside of the throat, the discharge from the nostrils is increased.

The disease may be accompanied by an eruption of nodules, or vesicles on the skin, or nasal mucous membrane.

In severe and chronic cases multiple abscesses may form. This complication is indicated by emaciation and weakness. Such cases usually terminate in death. Severe inflammation and swelling in the region of the throat may terminate in strangulation and death. The death-rate is from one to three per cent.

_The preventive treatment_ consists in using all possible precautions to prevent the exposure of susceptible animals and practising the immunization of exposed animals. The curative treatment is princ.i.p.ally careful nursing.

Rest, a comfortable stall, nourishing feed and good care const.i.tute the necessary treatment for the average case of distemper. When the abscesses become mature, they should be opened and washed with a disinfectant.

Steaming the animal several times daily relieves difficult breathing and the irritated condition of the mucous membranes. In case the abscesses do not form promptly and the throat is badly swollen, a blistering ointment or liniment may be applied. Bitter and saline tonics, the same as recommended in the treatment of indigestion, may be given with the feed.

INFLUENZA (CATARRHAL OR SHIPPING FEVER).--This is a well-known acute infectious disease of solipeds. It is characterized by depression, high body temperature and catarrhal inflammation of the respiratory and other mucous membranes.

Several epidemics of influenza have occurred in the United States. The most serious epidemic occurred in the latter part of the '70's, and the last one in 1900-'01. Influenza is present in the princ.i.p.al horse centers in a somewhat attenuated form.

_The specific cause_ of the disease has never been determined. The virus is present in the expired air, nasal secretions and excreta. Close proximity to a diseased animal is not necessary in order to contract the disease.

Stables may harbor the infection, and it may be distributed by such disease carriers as blankets, harness, clothing of the attendant and dust.

_The predisposing causes_ are cold, exposure and changes in climate. When the disease appears in a country, it is first present in the large cities, and from there it is scattered to the outlying districts. The _period of incubation_ is usually from four to seven days.

_The early symptoms_ of the disease are a high fever, marked depression and partial or entire loss of appet.i.te. The horse usually stands in the stall with the head down and appears sleepy. The visible and respiratory mucous membranes are inflamed, the respirations are quickened and the animal may cough. The eyes are frequently affected, the lids and cornea showing more or less inflammation. The digestive tract may be affected. At the beginning, colicky pains may be present and later constipation and diarrhoea. Symptoms of a serious nervous disturbance are sometimes manifested.

The limbs usually become swollen or filled. This disappears as the animal begins to improve. Pregnant mares may abort. The death-rate is low.