Part 88

4. That the comparatively small number of cattle which have aborted, suffered in health, or fallen off in condition after the test were either diseased before it was made or were affected by some cause other than the tuberculin.

THE SUBCUTANEOUS TEST (UNDER THE SKIN).

The most frequently used method of testing is the subcutaneous test, which consists in injecting the proper quantity of tuberculin underneath the skin into the subcutaneous tissue. If an animal is tuberculous, the action of the tuberculin causes a fever, which is indicated by a rise in temperature. This rise, under ordinary conditions, may occur any time between the eighth and twentieth hours after the tuberculin is injected, but in some cases it is desirable to measure the temperature before the eighth hour and continue to the twenty-fourth hour or longer.

The temperatures are measured at least 3 times in advance of the injection, at 2-hour intervals, to learn whether the animal is in proper condition to receive the test. The temperatures after injection are taken every 2 hours until the test is completed. The proper interpretation of the temperatures is made by the person applying the test, and a careful observance of any clinical changes is always important in determining the result. It can not be set forth too strongly that the test, including the two following methods, should be attempted only by those who are properly qualified to do the work.

THE INTRADERMIC TEST (INTO THE SKIN).

The intradermic test for detecting tuberculosis is used to a considerable extent, especially in area work and on range cattle not easily controlled. When made by those who have become skilled in its application, it is very accurate. In this test the tuberculin is injected between the layers of the skin, only a few drops being used, and it is usually applied in the region at the base of the tail, where the skin is soft and nearly hairless. The intradermic test is satisfactory also for the diagnosis of tuberculosis in swine and, when so used, the tuberculin is applied into the skin of the ear near its base.

The reaction from the intradermic test consists of a swelling at the point of injection and is observed from 72 to 150 hours after the injection. The character of the swelling varies, and a proper diagnosis of tuberculosis by this test can be made only by an experienced person.

THE OPHTHALMIC TEST (INTO THE EYE).

Still another method, known as the ophthalmic test, is used quite frequently and has been found to be of considerable value in what is known as "check" testing; that is, it is used in connection with either of the previously described methods. Sometimes a tuberculous animal that fails to react to those tests shows evidence of the disease upon the application of the ophthalmic test. The ophthalmic tuberculin is placed in one eye and the other eye is used as a check. A reaction is indicated by a characteristic discharge from the eye receiving the treatment, which may occur in from 3 to 10 hours after the application or even later. Some swelling and inflammation of the eye and lids are often noted.

TREATMENT OF TUBERCULOSIS.

Treatment of the disease is not seriously considered by any authorities at the present time.

The measures to be adopted to prevent the spreading of the disease must take into consideration not only the tubercle bacillus, but likewise all those circumstances that make cattle more susceptible to the disease, and which have already been dwelt upon. It would be useless to repeat here all that has been said above on the transmission of tubercle bacilli from one animal to another, and on the dangers of certain debilitating influences. A careful study of these influences will show how tuberculosis may, at least in some cases, be prevented. Great care should be bestowed upon the breeding, the surroundings, and the feed of the animal, so that the latter may be put into a condition to resist infection even when exposed to it. A tuberculin test should be applied to all strange cattle before they are introduced into the herd, and those which show a reaction should be refused.

A rigid exclusion of tuberculous animals is all that is necessary to prevent the appearance of the disease, provided cattle are not infected by consumptive persons and animals. The transmission of the disease from man to cattle is probably not frequent, but is regarded as a possible source of infection.

Tuberculosis in cattle must also be considered as bearing upon tuberculosis of other domesticated animals, particularly hogs. In Europe and the United States this disease is not uncommon among hogs, and appears to be on the increase. The reason for its existence may be looked for in the feeding of pigs with skim milk, buttermilk, and whey from creameries, with the offal of the abattoirs, with the household refuse generally, and behind tuberculous cattle. If tuberculosis is common among cattle, it is likely to be transmitted to hogs kept in this way.

The carcasses of animals which have died of tuberculosis should be buried deeply so that they can not be eaten by other animals. This is likewise true of all organs or tissues of slaughtered animals containing tubercles. These should never be fed to other animals, such as hogs, dogs, and cats, and should either be destroyed by fire or deeply buried.

When any of the animals in a herd of cattle show evident symptoms of tuberculosis, or when the tuberculin test proves that they are affected with this disease, the best method of procedure in most cases is to have the affected animals slaughtered and the stables disinfected. A large proportion of the animals which are slightly affected yield carcasses which are perfectly wholesome and fit for human food, but in all such cases there should be an inspection by an expert at the time of slaughter to determine which carcasses may be used and which should be destroyed.

The disinfection of stables may be accomplished by thoroughly cleaning them, scrubbing the floors with hot water, brushing down all loose dust from the walls, and tearing off all woodwork which is partly decayed. Then the whole interior of the stable should be covered with a good coat of limewash containing 1 part of formalin (which is a 40 per cent watery solution of formaldehyde) to 30 parts of the lime wash, or 4 ounces of formalin to each gallon of lime wash.

Similar precautions should be observed in removing the manure of the infected herd from the barnyard and other places accessible to cattle, since it is known that tuberculous cattle frequently eliminate large numbers of tubercle bacilli through the feces. The ground under the manure pile should then be disinfected, either by the above-mentioned formalin solution or by unslaked lime thickly sprinkled over the soil.

If all the animals which react are destroyed and the stables disinfected in this manner, the herd should remain free from the disease unless other affected animals are added to it. The introduction of the disease in this manner may be avoided by requiring a tuberculin test of all new animals admitted on the premises.

Unfortunately it is a fact that tuberculous animals which have been tested several times may become so accustomed to tuberculin that they will no longer react; consequently it is always advisable to purchase cattle from some one who is known to be reliable, as otherwise animals of this kind may be treated with tuberculin for the purpose of hiding the disease.

In the case of very valuable purebred animals and under exceptional circumstances it may be more advantageous to retain the reacting animals which are in good condition in order to breed from them and in that manner avoid the excessive loss which would follow from their immediate slaughter. This may be done if proper precautions are adopted.

The disposal of reactors depends upon the State laws and live-stock regulations of the State in which the herd belongs. If this policy is followed it should be attempted only after careful study of the plan known as the Bang method of controlling tuberculosis. The live-stock officials of the State should be frequently consulted and their advice followed; otherwise failure will surely ensue. The plan necessitates considerable trouble and is not recommended except under the circumstances mentioned.

BOVINE TUBERCULOSIS AND THE PUBLIC HEALTH.

The increasing amount of evidence pointing to the identity of human and animal tuberculosis, combined with the extraordinary mortality of human beings from this disease, often amounting to 10 to 14 per cent, has raised the question in all civilized countries as to how far animal, and especially bovine, tuberculosis is to blame for this high mortality. The medical and veterinary professions have approached this problem with equal zeal, and much has come to light within recent years which enables us to come to some conclusion. If this disease is transmitted from animals to man, how does the transmission take place? As comparatively few people come in direct contact with tuberculous cattle, it must be either through the meat, the milk, the butter, the cheese, or through all these products that the virus enters the human body. The question has thus narrowed itself down to the food products furnished by cattle.

It has become a very urgent question, especially in the poorer countries of Europe, whether all flesh from tuberculous animals is unfit for human food. It is argued there that if it can be shown that in the majority of cases of tuberculosis the bones and the muscular system are free from infection, there is no reason why the meat should not be put on sale under certain restrictions. The question may be resolved into two divisions: (1) How frequently does the disease invade those parts of the body which are used as food? (2) When the disease process is manifestly restricted to the internal organs, do tubercle bacilli circulate in the blood and lymph and can they be detected in the muscular tissue?

(1) Disease of the bones is not unknown, although very rare. According to Walley, it appears chiefly in the spongy bones of the head and backbone and in the long bones of the limbs. Occasionally the ends of the bones, where they are covered by the synovial membrane of the joints, are dotted with tubercles. The muscular system itself is very rarely the seat of tuberculous deposits, although the lymphatic glands lying near and among the muscles may be not infrequently diseased.

(2) Whether tubercle bacilli are found in muscle juice independent of any tuberculous deposits is a question which must be approached experimentally. There is on record a great variety of opinions on this matter, some authorities considering all flesh from tuberculous animals unfit for food, while others hold a contrary view. Experiments have shown that in rare cases the flesh of tuberculous cattle contains a small number of tubercle bacilli. In Germany the flesh of animals in which the disease is just beginning, or in which it is restricted to one or more related organs, is not rejected. When, however, the disease has affected the muscles or bones, or lymphatic glands situated on or between them, the flesh is condemned as unfit and dangerous. Animals are also rejected in which it is evident, from the general distribution of tubercles throughout the various organs, that the bacilli have been distributed by the blood and may have been carried into the muscular system (generalized tuberculosis).

Concerning the infectious nature of milk secreted by tuberculous cows, authorities have universally agreed that when the udder itself is in the slightest degree involved the milk possesses infectious properties, and is therefore dangerous. Tubercle bacilli in large numbers have been found in the milk and the udder under such circumstances. Unlike other affections of the udder, tuberculosis of this organ does not at once change the appearance and the quality of the milk secreted. Bang states that for at least a month after the disease has appeared the milk is normal in appearance and may be consumed and sold without arousing the suspicion of the owner. Considerable danger is, therefore, involved in this disease, and the necessity for the careful inspection of dairy cows seems more urgent than ever.