Special Report on Diseases of the Horse Part 67

SURRA.

By CH. WARDELL STILES, PH. D.

_Professor of Zoology, United States Public Health Service._

Surra is not known to occur in the United States, but it is more or less common in the Philippine Islands and India. It is caused by a microscopic, flagellate animal parasite, known as _Trypanosoma evansi_, 20 to 34 long by 1 to 2 broad, which lives in the blood and destroys the red blood corpuscles. In general the disease is very similar to and belongs in the same general cla.s.s with tsetse-fly disease, or nagana, of Africa and mal de caderas, of South America.

Surra is a wet-weather disease, occurring chiefly during or immediately after heavy rainfalls, floods, or inundations.

Surra attacks especially horses, a.s.ses, and mules, but it may occur in carabao, camels, elephants, cats, and dogs, and has been transmitted to cattle, buffaloes, sheep, goats, rabbits, guinea pigs, rats, and monkeys. No birds, reptiles, amphibia (frogs, etc.), or fish are known to suffer from it. It attacks both male and female animals, young and old. Australian breeds of horses and white and gray mules are said to be more susceptible than animals of other breeds and color.

Surra in equines and camels is said to be an invariably fatal disease, but cattle occasionally recover from it. There is no history of a definite onset of the disease, and the condition is progressive, usually with a number of relapses. The period of incubation may vary somewhat; in experimental cases it is from 2 to 75 (usually 6 to 8) days, according to conditions. The duration varies with the species of animal attacked, their age, and general condition. The average duration in the horse is reported at less than two months, though some cases may terminate fatally in less than one to two weeks.

_Method of infection._--All evidence now available seems to indicate that surra is strictly a wound disease, namely, that the parasite may enter the body only through a wound of some kind. Apparently by far the most common method is through wounds produced by biting flies whose mouth parts are moist with the infected blood of some animal bitten by the same flies immediately before biting the healthy animal. Crows may also transmit the infection by pecking at sores on a diseased animal, soiling their beaks with blood, and transferring this infected blood to a healthy animal. Likewise, if a scratch is made on a horse and then infected blood is rubbed on the scratch, the horse will become diseased.

If, in experiment, infected blood is fed to a healthy animal, the latter may contract surra in case it has an abraded or wounded spot in the mouth; but if no part of the lining of the alimentary ca.n.a.l is wounded, infection does not take place. Thus dogs and cats may contract the disease by wounding the lining of the mouth (as with splinters of bone) while feeding on the carca.s.ses of surra subjects. All available evidence indicates that under normal conditions of pregnancy the disease is not transmitted from mother to fetus.

There is a popular view that surra may be contracted by drinking stagnant water and by eating gra.s.s and other vegetation grown upon land subject to inundation, but there is no good experimental evidence to support this view: Probably the correct interpretation of the facts cited in support of this theory is that biting flies are numerous around stagnant water and in inundated pastures; hence, that a great number of possible transmitters of the disease are present in these places.

_Symptoms._[7]--The invasion of this disease when contracted naturally is usually marked by symptoms of a trivial character; the skin feels hot, and there may be more or less fever; there is also slight loss of appet.i.te, and the animal appears dull and stumbles during action; early a symptom sometimes appears which may be the first intimation of the animal's indisposition, and which, as a guide to diagnosis, is of great importance; it is the presence of a general or localized urticarial eruption. If the blood is examined microscopically, it may be found to present a normal appearance; but in the majority of cases a few small, rapidly moving organisms will be observed, giving to the blood, as it pa.s.ses among the corpuscles, a peculiar, vibrating movement, which if once observed will not easily be forgotten. If the parasite has not been discovered in the blood for several days, the symptoms mentioned above may be the only ones noticed, and, as a rule, when treated with febrifuges, the horse quickly improves in health and the appet.i.te returns. This condition does not last for more than a few days, when the animal is again observed to present a dull and dejected appearance, and on examination well-marked symptoms are found; the skin is hot, the temperature more or less elevated--101.7 to 104 F.; the pulse full and frequent--56 to 64 beats a minute; the visible mucous membranes may appear clean, but the conjunctival membranes, especially those covering the membrana nict.i.tans, are usually the seat of dark-red patches of ecchymosis, varying in size in different animals. There is more or less thirst and slight loss of appet.i.te; the animal eats its grain and green gra.s.s, but leaves all or a portion of the hay with which it has been supplied. At the same time there are slight catarrhal symptoms present, including lacrimation and a little mucous discharge from the nostrils.

Occasionally at this period of the disease the submaxillary glands may be found enlarged and perhaps somewhat tender on manipulation. One symptom is markedly absent, namely, the presence of rigors or the objective sign of chilliness. In addition, it will be noted that there is some swelling and edema of the legs, generally between the fetlock and the hock, which pits but is not painful on pressure, and in case of horses there may be also some swelling of the sheath at this stage of the disease. When the fever and concomitant symptoms have declared themselves for a short period, one thing becomes especially noticeable in every animal attacked, namely, the rapidity with which it loses flesh. If the blood has been examined microscopically during the second period of fever, at first a few parasites will have been observed in it, which day by day increase in number and reach a maximum, where they remain for a varying period, or at once suddenly or gradually disappear during the period of apyrexia. After the fever and the accompanying symptoms have for the second time been present for a few days--the period varying from one to six--the animal is found to have lost the dull, dejected appearance and to look bright. The temperature has fallen and, in some cases, has attained normal or even subnormal limits. The visible mucous membranes are clean, and the conjunctival petechiae begin to fade; the pulse, however, will be found to be weak and thready in character, but the appet.i.te excellent, and, in fact, if it were not for the loss of flesh and slight edema of the legs, there would be little to show that the animal was sick. Unfortunately, however, this condition does not continue for any great length of time, for again the temperature is elevated; in the course of a few hours the thermometer registers a still higher degree, the animal is dull and dejected, and by the following day the visible mucous membranes present a yellow tinge; large ecchymoses, dark in color, appear on the conjunctival membranes, the action of the heart is irritable, the pulse full and quick, or at times intermittent, and regurgitation may be observed in the jugulars, the breathing is quickened, and the individual respirations are shallow.

On watching an animal in this condition it may be noticed that it takes seven or eight very short inspirations, followed by a much more prolonged and sonorous one; at the same time the breathing is more abdominal than thoracic in character. On examination of the legs it will be found that the swelling and edema have increased considerably, and that on the under surface of the abdomen, where previously it was confined to the sheath, it has now commenced to spread forward along the subcutaneous tissue between the skin and the muscles. During the whole of this time the appet.i.te will have varied little, and the evacuations will be only slightly, if at all, altered in character. In the blood a repet.i.tion of the previous events takes place, the parasites make their appearance and increase to a maximum and again suddenly or gradually disappear, according to the length of the fever period. These periods, alternating with and without fever, may go on for a considerable time.

The progress of the disease is variable and greatly depends upon the condition of the animal attacked, the weak one succ.u.mbing very rapidly, but each return of the fever brings with it, as a rule, an increase in the severity of the symptoms. There is increased yellowness of the membranes, fresh crops of petechiae on the conjunctiva, a collection of gelatinous material at the inner angle, which at times becomes red in color from an admixture of blood, and which on microscopic examination is found to contain a varying number of the surra parasites; increased swelling and edema of the extremities and abdomen, which now extends between the fore limbs and up the chest. During this time the wasting has been steadily progressive, especially of the muscles of the back and those surrounding the hip joint and the glutei.

Toward the termination of the disease it will be noticed that an animal is disinclined to move, and when made to do so there is manifest loss of power over the hind quarters, somewhat simulating a slight partial paralysis, and the hind quarters of the animal reel from side to side.

In connection with this it may be noted that frequently there is paralysis of the sphincter ani and a dilated condition of the a.n.u.s.

These symptoms taken together point to some interference with the normal functions of the spinal cord in the lower dorsal and lumbar regions, and are probably owing to pressure caused by an exudation within the spinal membranes. In many cases shortly before death the heart's action becomes exceedingly violent, shaking the whole frame at each beat, so that the sound can be heard at some distance from the animal. In some of these cases the animal may suddenly drop dead; in others the emaciation and weakness become so p.r.o.nounced that it falls to the ground, and, after a short struggle, succ.u.mbs to the disease. In other cases, again, the animal falls to the ground and appears to be suffering from acute pain, struggles violently, sweat covers the body, and respiration is very hurried. The struggles soon exhaust the patient's strength, and for a time it lies quiet; soon, however, the struggles commence again, continuing until death occurs. In some cases the appet.i.te is voracious.

The symptoms of the disease as observed in experimentally inoculated animals are as follows: Twenty-four hours after the subcutaneous injection of a small quant.i.ty of surra blood, in the great majority of cases, a small circ.u.mscribed and somewhat raised swelling is noticed at the seat of the inoculation. After forty-eight hours the tumor has increased in size and is accompanied with some edema; it presents a certain amount of tension of the parts involved, and is generally tender on manipulation. These conditions continue to increase, until by the fourth day the tumor may measure 3 or 4 inches in; one direction by 2 or 3 in the other, and raised to the extent of an inch or an inch and a half above the surrounding tissues, or in some cases the tumor presents an almost circular form throughout. It will be also found that, if the tumor is firmly grasped, it is not fixed, but can be lifted up from the subcutaneous tissue. According to the nature and quant.i.ty of the inoculated blood, these symptoms rapidly present themselves, and either attain a maximum or are r.e.t.a.r.ded until, varying from the fourth to the thirteenth day, the tumor at the seat of inoculation will be found to have lost a certain amount of its tension and tenderness. From this date the swelling and edema gradually begin to grow less, until finally, after a period of 10 to 14 days, the only sign left of the former swelling is a slight thickening of the skin over the point of the injection; but at the moment when the tension and tenderness of the parts at the seat of inoculation become suddenly decreased a symptom of the utmost clinical importance takes place, namely, at that moment the parasite of surra enters the blood of the general circulation.

The temperature on the day of inoculation, and, in fact, for several days afterwards, may remain normal in character, there being only a few degrees difference between the morning and evening observations. In other cases there may be a slight rise from the first evening, and a gradual progressive rise until the swelling at the seat of inoculation shows signs of reduction in size, when the temperature generally takes a decided rise again, and may attain 104 or 105.8 F. This elevation will last a varying period of from two to six days, and on the day following its onset the ordinary symptoms of fever will be noticed, and in addition there will be petechiae on the conjunctival membranes, lacrimation, a slight mucous discharge from the nose, and in severe cases some edema of the lower portion of the legs, and perhaps of the sheath in horses. At the termination of the period of fever the temperature will be found to have fallen to normal or nearly so; the animal will present a brighter aspect, and there is every appearance of its return to health; in a few days, however, the animal again appears dull and half asleep; the temperature is elevated, a relapse takes place, and a repet.i.tion of all the symptoms in the primary paroxysm, including the reappearance of the parasite, is observed.

_Diagnosis._--A diagnosis may also be established by the complement-fixation or agglutination tests with the sera from suspected animals. This, however, can be carried out only in laboratories and requires special facilities for its execution.

_Treatment._--No satisfactory treatment is known. Intravenous injections of Fowler's solution of a.r.s.enic give temporary relief, but relapses occur. In view of the great economic importance of this disease, it would not be advisable to attempt to treat any sporadic cases should they occur in this country. On the contrary, the animals should be slaughtered immediately and their carca.s.ses promptly burned.

OSTEOPOROSIS OR BIGHEAD.

By JOHN R. MOHLER, V. M. D., _a.s.sistant Chief, Bureau of Animal Industry_.

Osteoporosis is a general disease of the bones which develops slowly and progressively and is characterized by the absorption of the calcareous or compact bony substance and the formation of enlarged, softened, and porous bone. It is particularly manifest in the bones of the head, causing enlargement and bulging of the face and jaws, thereby giving rise to the terms "bighead" and "swelled head," which are applied to it.

The disease affects horses, mules, and a.s.ses of all ages, cla.s.ses, and breeds, and of both s.e.xes, and is found under all soil, dietetic, and climatic conditions. It may occur in sporadic form, but in certain regions, such as South Africa, Australia, Madagascar, India, Hawaii, and in this country it seems to be enzootic, several cases usually appearing in the same stable or on the same farm, and numerous animals being affected in the same district. In the United States the disease has been found in all the States bordering the Delaware River and Chesapeake Bay, in some of the New England States, and in many of the Southern States, especially in low regions along the coast. In Europe the disease appears to be quite rare, and is usually described as a form of osteomalacia, a disease which is not uncommon among cattle of that continent. The opinion that bighead is only a form of osteomalacia, however, can not be accepted, nor can the infrequency of the former among European horses and the frequency of the latter among other live stock be conceded on the argument which has been presented, namely, that the better care which horses receive prevents them from becoming affected. In the Southwest, where osteomalacia, or creeps, has not infrequently been observed among range cattle by the writer, no case of osteoporosis of the horses using the same range has been noted, although the latter animals are given no more attention than the cattle.

The appropriate treatment of osteomalacia in cattle is so effective that if osteoporosis were a similar manifestation of disease a similar line of treatment should prove equally efficacious. However, this is not the fact. On the other hand, the occurrence of osteomalacia on old, worn-out soil, or on land deficient in lime salts, or from eating feed lacking in these bone-forming substances, or drinking water with a lime deficiency, is in perfect accord with our knowledge of the disease. But osteoporosis may occur on rich, fertile soil, in the most hygienic stables, and in animals receiving the best of care and of bone-forming feeds with a proper amount of mineral salts in the drinking water.

_Cause._--The cause of this disease still remains obscure, although various theories have been advanced, some entirely erroneous, others more or less plausible; but none of them has been established. Thus the idea that feeding fodder and cereals poor in mineral salts and grazing in pastures where the soil is poor in lime and phosphates will cause the disease has been entirely disproved in many instances. Others have considered that the disease starts as a muscular rheumatism which is followed by an inflammatory condition of the bones, terminating in osteoporosis. The idea that the disease is contagious has been advanced by many writers, although no causative agent has been isolated. Numerous experiments have been made by inoculating the blood of an affected horse into normal horses without results. A piece of bone taken by Pearson from the diseased lower jaw of a colt was transplanted into a cavity made for it in the jaw of a normal horse, but without reproducing the disease. Petrone believes that the _Micrococcus nitrificans_ causes osteomalacia in man as a result of its producing nitrous acid, which dissolves the calcareous tissues, and when injected into dogs in pure culture a similar disease is produced. It is probable that if this work is confirmed a somewhat similar causative factor will be discovered for osteoporosis.

Elliott considers the latter disease to be of microbic origin, the result of climatic conditions, and divides the island of Hawaii into two districts, in one of which the rainfall is 150 inches annually, where bighead is very prevalent, and the second of which is dry and rarely visited by rain, where the disease is unknown. Removal of animals from the wet to the dry district is followed by immediate improvement and frequently by recovery. In the wet district horses in both good and bad stables take the disease, but in the dry districts no unfavorable or unhygienic surroundings produce the affection. As both native and imported horses are equally susceptible, there is no indication of an acquired immunity to be observed.

Theiler has recently stated that his experiments in transfusing blood from diseased to normal horses were negative, and has suggested that the causative agent may be transmitted by an intermediate host only, as in the case of Texas fever. He draws attention to this method of spreading East African coast fever, although blood inoculations, as in osteoporosis, are always without result. We know that coast fever is infectious, and that it can not be transmitted by blood inoculations, but is conveyed with remarkable ease by ticks from diseased cattle. That the cause has not been observed may be accounted for by its being invisible even to the high magnification of the microscope.

On some farms and in some stables bighead is quite prevalent, a number of cases following one after another. On one farm of Thoroughbreds in Pennsylvania all the yearling colts and some of the aged horses were affected during one year, and on a similar farm in Virginia a large proportion of the horses for several years were diseased, although the cows and sheep of this farm remained unaffected.

_Symptoms._--The commencement of the disease is usually un.o.bserved by the owner, and these symptoms which do develop are generally not well marked or are misleading unless other cases have been noted in the vicinity. Until the bones become enlarged the symptoms remain so vague as not to be diagnosed readily. The disease may be present itself under a variety of symptoms. If the bones of the hock become affected, the animal will first show a hock lameness. If the long bones are involved, symptoms of rheumatism will be the first observed, while if the dorsal or lumbar vertebrae are affected indications of a strain of the lumbar region are in evidence. Probably the first symptom to be noticed is a loss of vitality combined with an irregular appet.i.te or other digestive disturbance and with a tendency to stumble while in action. These earlier symptoms, however, may pa.s.s un.o.bserved, and the appearance of an intermittent or migratory lameness without any visible cause may be the first sign to attract attention. This s.h.i.+fting and indefinite lameness, involving first one leg and then the other, is very suggestive, and is even more important when it is a.s.sociated with a tendency to lie down frequently in the stall and the absence of a desire to get up, or the presence of evident pain and difficulty in arising.

About this time, or probably before, swelling of the bones of the face and jaw, which is almost constantly present in this disease, will be observed. The bones of the lower jaw are the most frequently involved, and this condition is readily detected with the fingers by the bulging ridge of the bone outside and along the lower edge of the molar teeth. A thickening of the lower jawbone may likewise be identified by feeling on both sides of each branch at the same time and comparing it with the thinness of this bone in a normal horse. As a result mastication becomes difficult or impossible and the teeth become loose and painful. The imperfect chewing which follows causes b.a.l.l.s of feed to form which drop out of the mouth into the manger. Similar enlargements of the bones of the upper jaw may be seen, causing a widening of the face and a bulging of the bones about midway between the eyes and the nostrils. In some cases the nasal bones also become swollen and deformed, which, together with the bulging of the bones under the eyes, gives a good ill.u.s.tration of the reason for the application of the term bighead.

Other bones of the body will undergo similar changes, but these alterations are not so readily noted except by the symptoms they occasion. The alterations of the bones of the spinal column and the limbs, while difficult of observation, are nevertheless indicated by the reluctance of the animal to get up and the desire to remain lying for long periods of time. The animal easily tires, moves less rapidly, and if urged to go faster may sustain a fracture or have a ligament torn from its bony attachments, especially in the lower bones of the leg. An affected horse weighing 1,000 pounds was seen by the writer to fracture the large pastern bone from rearing during halter exercise.

The animal becomes poor in flesh, the coat is rough and l.u.s.terless, and the skin tight and harsh, producing a condition termed "hidebound," with considerable "tucking up" of the abdomen. The horse shows a short, stilted, choppy gait, which later becomes stiffer and more restricted, while on standing a position simulating that in founder is a.s.sumed, with a noticeable drop to the croup. The animal at this stage usually lies down and remains rec.u.mbent for several days at a time. Bed sores frequently arise and fractures are not uncommon in consequence of attempts to arise, which complications, in addition to emaciation, result in death.

The disease may exist in this manner for variable periods extending from two or three months to two years. The termination of the disease is uncertain at best, but is likely to be favorable if treatment and a change of feed, water, and location is adopted in the early stages of the malady.

_Lesions._--As has been stated, the bones are the princ.i.p.al tissues involved. The nutrition of the bone is disturbed, as is indicated by the diminished density or rarefaction of the bony substances, the increase in the size or widening of the Haversian ca.n.a.l and the medullary cavity, and the enlargement of the network of s.p.a.ces in the spongy tissue, the absorptive changes following the course of the Haversian system. In this process of absorption there are formed within the substance of the bone areas of erosion, indentations, or hollow s.p.a.ces of irregular shape.

These s.p.a.ces increase in size and become confluent, causing an appearance resembling some varieties of coral. The affected bone may be readily incised with a knife, the cut surface appearing finely porous.

This porous area is soft, pliable, and yields easily to the pressure of the finger. It has been shown by chemical a.n.a.lysis that the bone of an osteoporotic horse, when compared with that of a normal horse, shows a reduction in the amount of fat, phosphoric acid, lime, and soda, but a slight increase in organic matter and silicic acid. The bones lose their yellowish-white appearance, becoming gray and brittle. The affected bones may be those of any region or portion of the body. Besides the change already noted in the bones of the face, the ends of the long bones, such as the ribs, are involved, and may be sectioned, though not so readily as the facial bones. The bones of the vertebrae are also frequently involved, necessitating great care in casting a horse, as the writer has seen several cases of broken backs in casting such animals for other operations. The marrow and cancellated tissue of the long bones may contain hemorrhages and soft gelatinous material or coagulated fibrin. The internal organs are usually normal, but a catarrhal condition of the gastrointestinal tract may be noted as the result of the improper mastication, resulting from the enlargement of the jaws and soreness of the teeth.

_Treatment._--The affected animal should be immediately placed under new conditions, both as to feed and surroundings. If the horse has been stable fed, it is advisable to turn it out on gra.s.s for two or three months, preferably in a higher alt.i.tude. If the disease has been contracted while running on pasture, place the animal in the stable or corral. In the early stages of the disease beneficial results have followed the supplemental use of lime given in the drinking water. One peck of lime slaked in a cask of water and additional water added from time to time is satisfactory and can be provided at slight expense. This treatment may be supplemented by giving a tablespoonful of powdered bone meal in each feed, with free access to a large piece of rock salt, or the bone meal may be given with four tablespoonfuls of mola.s.ses mixed with the feed. Feeds containing mineral salts, such as beans, cowpeas, oats, and cottonseed meal, may prove beneficial in replenis.h.i.+ng the bony substance that is being absorbed. Cottonseed meal is one of the best feeds for this purpose, but it should be fed carefully. The animal should not be allowed to work at all during the active stage of the disease, nor should it be used for breeding purposes.

FOOTNOTES:

[7] This summary of symptoms is based upon work by Lingard.

HORSESHOEING.

By JOHN W. ADAMS, A. B., V. M.,

_Professor of Surgery and Lecturer on Shoeing, Veterinary Department, University of Pennsylvania._

Bad and indifferent shoeing so frequently leads to diseases of the feet and in irregularities of gait, which may render a horse unserviceable, that it has been thought appropriate to conclude this book with a brief chapter on the principles involved in shoeing healthy hoofs.

In unfolding this subject in the limited s.p.a.ce at my disposal, I can only hope to give the intelligent horse owner a sufficient number of facts, based on experience and upon the anatomy and physiology of the foot and leg, to enable him to avoid the more serious consequences of improper shoeing.

Let us first examine this vital mechanism, the foot, and learn something of its structure and of the natural movements of its component parts, that we may be prepared to recognize deviations from the normal and to apply the proper corrective.

GROSS ANATOMY OF THE FOOT.

(Pls. x.x.xII-x.x.xIV.)

The bones of the foot are four in number, three of which--the long pastern, short pastern, and coffin bone, placed end to end--form a continuous straight column pa.s.sing downward and forward from the fetlock joint to the ground. A small accessory bone, the navicular, or "shuttle," bone, lies crosswise in the foot between the wings of the coffin bone and forms a part of the joint surface of the latter. The short pastern projects about 1-/2 inches above the hoof and extends about an equal distance to it. (See also page 395.)

The pastern and the coffin bone are held together by strong fibrous cords pa.s.sing between each two bones and placed at the sides so as not to interfere with the forward and backward movement of the bones. The joints are therefore hinge joints, though imperfect, because, while the chief movements are those of extension and flexion in a single plane, some slight rotation and lateral movements are possible.

The bones are still further bound together and supported by three long fibrous cords, or tendons. One, the extensor tendon of the toe, pa.s.ses down the front of the pasterns and attaches to the coffin bone just below the edge of the hair; when pulled upon by its muscle this tendon draws the toe forward and enables the horse to place the hoof flat upon the ground. The other two tendons are placed behind the pasterns and are called flexors, because they flex, or bend, the pasterns and coffin bone backward. One of the tendons is attached to the upper end of the short pastern, while the other pa.s.ses down between the heels, glides over the under surface of the navicular bone, and attaches itself to the under surface of the coffin bone. These two tendons not only flex, or fold up, the foot as the latter leaves the ground during motion, but at rest a.s.sist the suspensory ligament in supporting the fetlock joint.