Jan. 21 Luther Adams, Boston, Mass........ Liverpool, England... Sussex Aberdeen-Angus ... STATION FOR THE PORT OF BALTIMORE, ST. DENIS, MD. [Dr. A. M. Farrington, Acting Veterinary Inspector.] Liverpool, England... Galloway. June 24 Clark Maxwell, Winchester, Va. 11 14 The following shows the whole number of cattle received at the various stations from January 1, 1889, to January 1, 1890: No contagious disease appeared among the cattle at any of the stations during the year, and the general health of all the animals imported was good. INOCULATION AS A PREVENTIVE OF SWINE DISEASES. Inoculation with hog cholera virus was first tested as a preventive for this disease in the experiments of the Bureau of Animal Industry in the year 1886. The method of inoculation was discovered at that time, but the results were unsatisfactory, as the animals were not sufficiently protected, and the experiments have been repeated under various conditions from that time to the present to learn if any modification of the operation would make it more effectual. Prevention by inoculation depends on the well-known principle that one attack of a contagious disease generally protects the individual from subsequent attacks of the same contagion. The amount of protection received varies greatly with different diseases and different animals. In no case are all individuals protected in this way from any disease, and in many cases the immunity lasts only for a short period of time. Inoculation in practice consists in injecting under the skin as much of the strong virus of hog cholera as can be given without producing a fatal attack of the disease. Inoculation is very different from vaccination. The virus used in inoculation is the same in variety and strength as that found in animals dying with the plague, while for vaccination a weakened virus is used, which can not cause a fatal disease. No method of vaccination has yet been introduced for the hog diseases of this country. Inoculation is now being advocated as a preventive for hog cholera, and it should be remembered that this means the introduction into the animal's body of the strong virus of the malady, and it is only a question of the size of the dose whether the disease produced by this operation is mild or fatal in its character. The dose is not the only factor which influences the result that follows inoculation. The strength of the virus varies so much in different outbreaks of the same disease, that a perfectly harmless dose obtained from one outbreak would be certainly fatal when obtained from another. There is another influence which has an even greater effect in varying the results of inoculation, and that is the wide difference in the susceptibility of the animals. A dose of virus that will scarcely affect one animal will kill another in the same herd, and there is also such a great difference in the susceptibility in different herds that the dose which might be used on one herd without producing any noticeable effects would set up a disease in another herd and cause the loss of a majority of the animals. With these varying conditions, which in many cases can neither be foreseen nor controlled, inoculation is an operation which is attended with more or less danger of producing the very disease which we are seeking to avoid. In our experiments we found that a dose of 1 cubic centimeter, i. e., from 15 to 20 drops, of the strongest cultivated virus would occasionally kill an animal. From one-quarter to one-half this quantity, i. e., from 4 to 10 drops, have been given without serious consequences in any case. Such doses generally produce a swelling where injected, which is at first warm and more or less painful, and later becomes encysted. The center softens, disintegrates and becomes a purulent mass, which may remain encysted or may force an opening through the skin and discharge for several weeks. An inoculation of this kind produces a slight degree of immunity, because a second inoculation can then be made with two or three cubic centimeters of virus, i. e., with four to twelve times the first dose, and still no fatal effects result. The second inoculation increases the immunity, but still the animals are not able to resist the effects of feeding with strong virus or exposure in pens where sick animals are kept. We inoculated about fifty animals in this way in our first experiments, varying the doses somewhat, and only five of them resisted the first exposure. By giving two inoculations we, of course, get a greater degree of protection than can possibly be obtained from one inoculation, with safety to the animals, but the expense of two inoculations is so great that, in order to make the method practical, the inoculator gives only one dose and generally increases that beyond the limit of safety. Thus, in some experiments that have been made in the West, I am informed that a dose of 1 cubic centimeter, i. e., from 15 to 20 drops, was given, and many herds contracted the disease and died, as should have been anticipated from the experiments previously made by the Bureau of Animal Industry. In view of these facts, when any one comes before the farmers of the country and recommends inoculation, it is well to inquire whether he is interested in the operation from a pecuniary point of view. The question as to how much the farmer will save by the adoption of this method of prevention is uncertain, and opens a wide field for discussion, but the sum it will be necessary for him to pay out to the experts who must be employed can be very accurately figured. This is one of the most practical aspects of the question and should under no circumstances be overlooked. H. Mis. 270-2 It has been asserted that as many as one hundred and four hogs have been inoculated in seventy-two minutes. At a cost of 50 cents a head, which is the amount now charged for inoculation, this would reach the sum of $43.33 an hour for the services of the inoculator, which certainly appears to be more than those engaged in the hograising industry can afford to pay for professional assistance. Should inoculation be generally adopted in the States in which hog raising is most largely carried on, it would require at least fifty men working five hours a day to comply with the demands. These men, inoculating eighty hogs an hour each, would inoculate a total of twenty thousand hogs a day, which would yield a daily revenue of $10,000. The total cost of hiring fifty men and maintaining a labora tory to supply virus would hardly exceed $300 a day. Putting the expenses at the liberal sum of $500 a day, the net profit to those conducting the inoculations would be $9,500 a day. The inoculation of but a small portion of the hogs in the chief hog-raising States of the country would therefore yield a profit to the inoculator of about $3,000,000 per annum, a sum which is sufficient to account for many of the enthusiastic and exaggerated statements of the benefits to be derived from inoculation which have appeared in public prints. It has been shown by our experiments and by those of other investigators, that if a sufficient dose of virus is given to produce any degree of immunity the hog will be more or less stunted, and if the strong virus is used there is great danger of infecting the ground. Now, these two faults are inherent in the method; they can not be avoided, and it is impossible to so improve the operation as to overcome them. About a year ago an attempt was made to demonstrate the success of inoculation by inoculating one thousand hogs belonging to farmers in Nebraska. There had been quite a controversy between parties in that State for more than a year as to the merits of the operation, and undoubtedly every precaution known to the operators was practiced to secure a successful issue for this experiment. The director of these experiments afterwards reported in the Nebraska State Journal of December 16, 1888, that one party who had 260 hogs inoculated had lost 220. Another farmer who had 46 inoculated lost "nearly all." Still another who had 121 inoculated lost a large number," while a fourth, who had 93 inoculated, lost "all but 18 or 20." It is evident from these statements that out of the 1,000 hogs inoculated, the loss was very little, if any, less than 400 head. The disease in these cases appeared in the inoculated herds from ten to fifteen days after the inoculation, and was evidently introduced in most if not in all cases by this operation. These experiments show that inoculation is attended with very considerable danger to the health and lives of the animals operated upon. It is no doubt possible to so reduce the dose of the virus as to prevent this heavy mortality following the inoculation, but in that case the protection would be correspondingly less. Leaving out of consideration the question of whether the hog, in case he survives the inoculation, is protected from the disease, it is plain that an operation which is followed by four hundred deaths out of a thousand inoculations has not been sufficiently perfected to merit the confidence of the farmers. We will now turn for a moment to the question of the protection by the operation. To what extent were the hogs inoculated in Nebraska protected from the contagion, if really exposed to it? The advocates of inoculation tell us that it has been impossible for them to give the disease to their inoculated hogs. Our experiments at Washington show that nearly all inoculated hogs can be afterwards fatally infected with cholera. Did the animals inoculated in Nebraska receive any greater degree of immunity than those which were inoculated in Washington? The Board of Inquiry appointed by the Commissioner of Agriculture in 1888 procured a number of hogs that had been inoculated in Nebraska (about seventeen), and tested them by feeding them with cultivated virus of hog cholera and by inoculating them with the virus of hog cholera and swine plague. In each case a number of the animals that had not received the protective inoculation were used in the experiments to determine the effect of exposure upon ordinary swine. The first test was made by feeding cultivated virus, but this did not prove strong enough to kill any of the hogs. Even those which had not been inoculated survived, but all of the hogs, including those that had been inoculated, were very sick. The inoculated hogs were not quite as sick as the others, but there was very little difference. Four of the inoculated hogs from Nebraska, and five hogs. from Pennsylvania which had not previously been inoculated, were then inoculated with the virus of the disease known as infectious pneumonia or swine plague. Of the four Nebraska inoculated hogs, three died and one recovered, but this one when subsequently killed for examination proved to be very severely affected. Of the five hogs which had not been previously inoculated one died and four were sick and recovered. When killed for examination one of the four was found seriously diseased, the three others were either slightly or not at all affected. Still later four Nebraska inoculated hogs and two other hogs which had not been inoculated were fed upon the viscera of hogs which had died of hog cholera. Two of the inoculated hogs and the two that had not been inoculated contracted hog cholera and died. Two of the inoculated hogs remained well. As a last test, the remaining six animals from Nebraska were inoculated by intravenous injection of the cultivated virus of hog cholera. Of these, three had been inoculated with hog cholera virus, one had been inoculated with the sterilized liquids in which hogcholera germs had grown, and two had recovered from an attack of hog cholera. The four hogs which had received the protective inoculation all died. One of the recovered hogs died and the other resisted the virus and remained well. It is quite evident from these experiments that the animals inoculated in Nebraska were fully as susceptible to hog cholera after the operation as were those which had been inoculated in the experiments of this Bureau in Washington. The conclusion that inoculation is not a satisfactory preventive for hog cholera is by no means inconsistent with the results obtained in investigating other diseases. Various experiments have shown that the protection which follows one attack of a disease or which is produced artificially by inoculation or vaccination is by no means absolute. It is simply an increased power to resist that particular contagion, and it may be sufficient to guard against the small doses of the virus which with most diseases are all that an animal is exposed to under ordinary conditions. But if from any cause a larger quantity of the contagion finds its way into the animal's body it will contract the disease in a fatal form in spite of the immunity derived from a previous attack or from inoculation. This was strikingly shown in the writer's experiments with fowl cholera (Report Department of Agriculture, 1881-'82, p. 289) and by the researches of Professor Chauveau with anthrax. While therefore it may be perfectly practical to prevent by inoculation those diseases in which the contagion does not multiply outside of the body, and with which the attack is caused by a small quantity of virus floating in the air or adherent to the wood-work of buildings, it may be much more difficult or impossible to prevent that other class of diseases to which hog cholera belongs, and which are caused by germs that multiply freely in water, in the soil, and in moist organic matter, and which are consequently taken into the body in enormous quantities, especially by swine. There is another very important consideration which bears upon the practicability of preventing swine diseases by inoculation. Hogs inoculated with hog-cholera virus do not receive the slightest degree of protection from any other disease. As there are at least two contagious diseases of hogs in this country, both of which are widely scattered and fatal, we can not hope by any single inoculation to prevent all the losses caused by contagious diseases of swine. To inoculate for two diseases would double the expense, and this would be a very serious objection to such a method of prevention. The existence of two diseases has been very vigorously denied, but the conclusions of the Bureau of Animal Industry on this subject have now been confirmed not only by the Board of Inquiry appointed to consider this question, but also by Professor Welch, the eminent pathologist of Johns Hopkins University. In the future, therefore, the conclusions as to the economy of preventing swine diseases by inoculation must be based upon the assumption that there are at least two diseases, each of which will require a special inoculation for its prevention. This brings us to the final test which must be applied to all methods of prevention, and that is their economic results. We will now consider inoculation from this point of view. Leaving out of consideration for the present the many reasons for believing that inoculation is a dangerous operation, and that it does not do what is claimed for it in the way of prevention, we will compare the cost of preventing hog cholera by this operation with the amount of the loss caused by this disease. According to the estimates of the Statistical Division there are about 50,300,000 hogs in the United States. The inoculation of these at 50 cents per head would cost $25,150,000. The total loss from disease during the year 1888 was 3,105,000 hogs at an average value of $5.79 each. This would make the total loss of swine from all diseases $17,980,000. In order to estimate the loss from hog cholera we must deduct from this sum the losses from ordinary diseases, such as animal parasites, exposure, overcrowding, and improper feeding, which are always acting and do not produce epizootic diseases. These losses were estimated by the Statistician of the Department in 1886 to be about 4 per cent. of the total number of hogs, but as this may be considered rather a large estimate, we will in our calculation take 3 per cent. as the average loss from such causes. This would amount in 1888 to 1,509,000 animals, valued at $8,737,000, and deducting this from the total loss of swine, we have remaining $9,243,000 as the losses from epizootic swine diseases. In the present condition of our knowledge we must admit that there are at least two entirely distinct |
