application of tuberculin, viz: Can the reaction produce a worse
condition in tuberculous animals than before existed? Hess emphatically
states that it can, and on this account he earnestly warns against its
application. My attention has been directed to this question from the
beginning. In my first publication on tuberculin injection I reported two
cases in which acute miliary tuberculosis was proved in two high-grade
tuberculous cows several weeks after the tuberculin injection. I then
stated my suspicion that perhaps the tuberculin injection had some
connection with this, just as is often supposed to be the case in human
practice. With my present very large amount of material for observation
at hand I may express the following opinion: Such an acute development of
tuberculosis as a result of tuberculin injection is to be feared only
exceptionally, and then in cases of advanced tuberculosis. _It must not
be forgotten that acute miliary tuberculosis by no means rarely
accompanies an advanced tuberculosis of long standing._ It is therefore
impossible to offer strict proof of the causal connection with the
injection, and only oft-repeated observation could make this probable.
In support of my view I offer the following: In the course of the last
three years I have made careful post-mortem examinations of 83
tuberculous animals, which have been removed from my experiment farm,
Thurebylille. Among these were 18 (or, strictly speaking, 23) high-grade
tuberculous animals. I have been able to prove miliary tuberculosis in
only 4 of these. Among the others, which showed less developed
tuberculosis, I have never found miliary tuberculosis, and with very many
I have never found any sign of a more rapid development of the process.
On the contrary, it has been proved that the disease was restricted
locally, often for years, in spite of yearly repeated injections.
Dissections were made at very different periods after the injections--in
17 cases from 4 to 12 days after the last test. In all of these cases
earlier tests had been made months or years before. In 28 cases the
injection took place from 19 days to 2 months before the butchering; in 3
of these cases earlier injections had been made. In 38 cases from two and
one-half months to one year intervened between the last injection and the
dissection. Dissection gives the best explanation of this question, but a
clinical observation, continued for years, of a herd tested with
tuberculin can render very essential aid. If Hess's opinion is correct,
it is to be assumed that tuberculosis must take an unusually vicious
course in such herds, but this I have been unable to prove. At
Thurebylille there has existed for three years a reacting division,
consisting originally of 131 head and now 69. Although these animals are
yearly tested, and although most of them react every year, the division
certainly appears to be made up of healthy animals, and the farm
inspector has expressed the decided opinion that the tuberculosis in this
division is no more developed than at the beginning of the experiment.
The testimony of many owners of large herds of cattle which have long ago
been injected is to the same effect. I will adduce statements from
several. A farm tenant whose cattle were injected 20 months previously,
when 82 per cent of the grown animals reacted, wrote me recently as
follows: "Only 2 cows from the division of 100 head had been sold as
decidedly tuberculous. The majority appeared afterwards, just as before,
entirely healthy. The fat animals which had been slaughtered had been
pronounced healthy by the butchers." Another farm tenant with a herd
injected in 1894 had not been obliged to remove a single animal from the
tuberculosis division, numbering 70 head. A large farm owner in Jutland
stated in September that he had traced no undesirable result from the
injection. His herd of 350 had been injected in February and about 75 per
cent reacted. Similar answers have been given by other owners and
veterinarians.
A veterinarian who had injected 600 animals, among them a herd of a large
farm, 18 months previously, expressed the belief that the injection had
produced in no single case an unusually rapid or vicious course of
tuberculosis. In spite of a demand made months ago, I have received thus
far no report from any veterinarian of an undesirable result.
On a large farm, on which before the injection tuberculosis had appeared
in a vicious form, the owner had the impression that the severe cases had
afterwards become more numerous. He had, however, not suffered severe
losses, and 8 months later the large reacting division by no means made a
bad impression. Finally, it is to be noticed that tuberculin has been
employed on a large scale in Denmark for years, and still the demand from
farmers constantly increases. This could certainly not be the case if the
injections were generally followed by bad results.
Paige said, after the tests of the herd of the Massachusetts Agricultural
College, that "its use is not followed by any ill effects of a serious or
permanent nature."
Lamson, of the New Hampshire College Agricultural Experiment Station, said:
"There is abundant testimony that its use is not in any way injurious to a
healthy animal."
Conn, who made a special study of the present attitude of European science
toward tuberculosis in cattle, reached the following conclusions:
It has been, from the first, thought by some that the use of tuberculin
produces a direct injury upon the inoculated animals. This, however, is
undoubtedly a mistake, and there is no longer any belief anywhere on the
part of scientists that the injury thus produced is worthy of note. In
the first place, the idea that it may produce the disease in a perfectly
healthy animal by the inoculation is absolutely fallacious. The
tuberculin does not contain the tubercle bacillus, and it is absolutely
certain that it is impossible to produce a case of tuberculosis in an
animal unless the tubercle bacilli are present. The use of tuberculin,
therefore, certainly can never produce the disease in the inoculated
animal.
It has been more widely believed, however, that the inoculation of an
animal with this material has a tendency to stimulate an incipient case
of tuberculosis. It has been thought that an animal with a very slight
case of the disease may, after inoculation, show a very rapid extension
of this disease and be speedily brought to a condition where it is
beyond any use. The reasons given for this have been the apparent
activity of the tuberculosis infection in animals that have been
slaughtered shortly after inoculation. This has been claimed, not only
by agriculturists who have not understood the subject well, but also by
veterinarians and bacteriologists. But here, too, we must recognize that
the claim has been disproved, and that there is now a practical
unanimity of opinion on the part of all who are best calculated to judge
that such an injurious effect does not occur. Even those who have been
most pronounced in the claim that there is injury thus resulting from
tuberculin have, little by little, modified their claim, until at the
present time they say either that the injury which they formerly claimed
does not occur or that the stimulus of the disease is so slight that it
should be absolutely neglected in view of the great value which may
arise from the use of tuberculin. Apart from two or three who hold this
very moderate opinion, all bacteriologists and veterinarians unite in
agreeing that there is no evidence for believing that any injury
results. In Denmark, especially, many hundreds of thousands of animals
have been inoculated, and the veterinarians say there is absolutely no
reason in all their experience for believing that the tuberculin
inoculation is followed by any injurious results.
In 1898 tuberculosis was found in the large Shorthorn herd belonging to W.
C. Edwards, of Canada, who with commendable promptness and public spirit
had his animals tested, and at once proceeded to separate the diseased from
the healthy animals. They were all finely bred animals, and of the very
class which we have been told are most susceptible to the injurious effects
of tuberculin. After using this test regularly for two years, Mr. Edwards
wrote as follows:
I have seen nothing to lead me to believe that the tuberculin test had
any injurious influence on the course of the disease. It is by no means
our opinion that the disease has been stimulated or aggravated by the
application of the tuberculin test. All animals that we have tested two
or three times continue as hale and hearty as they were previously, and
not one animal in our herds has broken down or failed in any way since
we began testing.
Mr. Edwards, in December, 1901, verbally stated that his views as to the
harmlessness of tuberculin remained unchanged, and that he had not seen the
least ill effect in any of his cattle from its use.
Those who have had most experience with tuberculin have failed to observe
any injurious effects following its use upon healthy cattle. With
tuberculous cattle it produces a fever of short duration, and in the great
majority of cases all derangement of the system which it causes disappears
within 48 hours after the tuberculin is administered. There appear to have
been a very few cases in which the disease was aggravated, and a greater
number in which it was benefited by the injection of tuberculin. The cases
of abortion following the tuberculin test have not been numerous, even when
cows were tested within a few weeks of the normal time of calving. The few
cases of this kind which have occurred may be explained by the fact that
abortion in cattle is a very common occurrence, and that it would
inevitably happen sometimes after the tuberculin test as a mere coincidence
and without any relation between the test and the loss of the calf. The
cases of abortion which have been cited appear to be no more numerous than
might be expected to have occurred among the same number of cattle within
the same period if the test had not been applied.
At the present time there is ample evidence to show that tuberculin is the
most reliable means of detecting tuberculosis in the living animal and that
its use is not attended by any harmful aftereffects.
An act of Congress was approved July 24, 1919, for the purpose of
controlling and eradicating tuberculosis of animals. The official means of
detecting tuberculosis in the living animal is the tuberculin test, which
may be applied by three different methods--the subcutaneous, the
intradermic, and the ophthalmic. It is not necessary to discuss here the
details of these three methods, which are made use of in the work of
eradication of tuberculosis.
The plan adopted by the State and Federal authorities in eradication of the
disease is known as "The Accredited-Herd Plan." Under this plan herds are
tested under State and Federal supervision, the diseased animals are
appraised, removed, and slaughtered under Federal inspection. Retests are
then made after definite periods of time until two successive tests show
all the animals to be free from the disease. At this time the herd owner is
given a certificate of an accredited herd.
Details concerning the accredited-herd plan may be obtained by applying to
the Chief of the Bureau of Animal Industry, Washington, D. C.
THE TUBERCULIN TESTS.
Testing animals with tuberculin is the process of introducing tuberculin
into the animal and interpreting results according to well-known
standards.
From the investigations and observations that have been mentioned, it may
be safely concluded--
1. That the tuberculin test is a wonderfully accurate method of
determining whether an animal is affected with tuberculosis.
2. That by its use the animals diseased with tuberculosis may be detected
and removed from the herd, thereby eradicating the disease.
3. That it has no injurious effect upon healthy cattle.
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.