VI. Vaccinations against symptomatic anthrax. Symptomatic anthrax, which is often confounded with true anthrax, is set up, as demonstrated by Arloing, Cornevin, and Thomas, by a specific anaerobic micro-organism to which has been given the name of Bacillus chauvaei. Immediately after the discovery of the attenuation of viruses and of vaccines against fowl cholera, the three observers above mentioned tried to apply it to symptomatic anthrax. Finally they devised a method which was soon adopted in practice, and which, for nearly twenty years, has been used in the vaccination of the Bovidae in countries where symptomatic anthrax is most prevalent. This is especially the case in mountainous districts, such as Switzerland, the Bavarian Alps, the Dauphiné, L’Auvergne, etc.
Arloing, Cornevin, and Thomas[789] prepare two vaccines against symptomatic anthrax by a method very different from that used in the preparation of the Pasteurian anti-anthrax vaccines. They take the virus from the muscles invaded by the micro-organism; they triturate a piece of the tumefied muscle in a mortar, adding to it a few drops of water. The mixture is filtered through muslin and the fluid dried at 37° C.; a virulent brown powder is thus obtained. In the preparation of the vaccines a portion of this powder is mixed with water and subjected to a temperature of 100°–104° C. for seven hours. Another portion is heated during the same number of hours to 90°–94° C. only. This latter forms the second vaccine whilst the first portion constitutes the first.
In practice the two vaccinal powders are dissolved in cooled boiled water and are introduced into the subcutaneous tissue of the animals that it is wished to immunise. The second vaccine should be injected 8 to 12 days after the first. The vaccines are usually tolerated very well by the Bovidae and confer upon them a definite and permanent immunity. In spite of certain drawbacks this method, known as the “Lyons method,” has proved to be a very serviceable one and is retained as the best devised up to the present. Its efficacy is proved by the fact that in the period from 1884 to 1895 in 400,000 vaccinated animals the mortality has only been 1 per 1,000. Arloing, Cornevin, and Thomas thought that raising the virus to a high temperature brought about a real attenuation.
Leclainche and Vallée[790], who have recently returned to the study of this question, have shown that this view cannot be maintained. In reality the spores, after being heated to 90°–104° C., gave rise to bacilli endowed with their normal and complete virulence. But the heating in the preparation of the Lyons vaccines destroys the toxin manufactured by the Bacillus chauvaei, with the result, that the spores now become the prey of phagocytes: it is for this reason and for this reason alone that the inoculation of these vaccines is so well tolerated. All the spores of the vaccinal powder are not eaten by the phagocytes: those which are found in the centre of solid particles of the powder offer a prolonged resistance to the action of the cells, and some of them germinating produce bacilli and give rise to a mild disease capable of conferring immunity. The germination of these spores is further facilitated by the presence of foreign micro-organisms in the vaccinal powders; these organisms help to interfere with the phagocytosis of the spores of symptomatic anthrax.
In the course of their researches, Leclainche and Vallée demonstrated that it is easy to vaccinate animals susceptible to anthrax and to confer on them a substantial immunity by means of a single protective injection of a pure culture of Bacillus chauvaei. For this purpose they use cultures grown in broth made from the pig’s stomach (“bouillon de panse” or Martin’s broth) which they heat for 2 hours at 70° C. The cultures, so treated and injected in quantities of 1 to 2 c.c. into Bovidae, induce in them an immediate immunity. These authors are persuaded that the vaccination by this method might be used on a large scale with certain advantages over the method at present in use. A single injection, instead of two, involves a great economy, and the injection of pure vaccinal cultures obviates the accidents caused by the foreign organisms which are found mixed with the Lyons vaccine.
On the other hand, Leclainche and Vallée think that vaccination by serums has no future in the fight against symptomatic anthrax and should only be used in exceptional cases.
It is evident that the Lyons method is capable of being improved and some day may be replaced by another. Still it must be remembered that it has already preserved a very great number of animals from certain death by symptomatic anthrax.
VII. Vaccinations against swine erysipelas. Swine erysipelas is a disease widely distributed in nearly all countries where the breeding of pigs is carried on on a large scale. It is a very fatal disease, and it is estimated that in France alone at least 100,000 pigs of the value of more than five million francs succumb to it annually. Unfortunately swine erysipelas is often confounded by breeders with other epizootic diseases, especially pneumo-enteritis of the pig. This confusion has often resulted in large losses to agriculture.
Soon after the vaccinations against anthrax became a part of veterinary practice, Pasteur[791], assisted by Thuillier, took up the study of swine erysipelas which was causing great ravages in the department of Vaucluse. They were not long in discovering that the true cause of the disease was a very small bacillus capable of growing in pure culture in nutrient broth. Guided by his former investigations, Pasteur with his collaborator undertook minute researches into the reinforcement and attenuation of the virulence of the bacillus of swine erysipelas which led them to the elaboration of a method of vaccination capable of conferring on pigs a high degree of protection against the disease. Following the line of the anthrax vaccinations, Pasteur and Thuillier prepared two vaccines against the erysipelas, the first more attenuated than the second. The bacilli of these two vaccines were cultivated in broth and sent out in tubes similar to those employed in the distribution of the anthrax vaccines.
The vaccines are in themselves innocuous and are capable of communicating to the inoculated pig an immunity sufficiently durable to be of real service. Young pigs being less susceptible to the erysipelas than are the adults, it is generally preferred to vaccinate young pigs of from two to four months. The vaccination is done at two separate times. The first vaccine, in a dose of one-eighth of a cubic centimetre, is inoculated subcutaneously on the inner aspect of the right thigh; the second vaccine is inoculated in the same way, 12 or 15 days later, into the left thigh. The immunity that follows these vaccinations is not fully established until the end of the second week.
In spite of the many advantages of the Pasteurian method the vaccinations against swine erysipelas have not spread so much as one might have expected; and they have found a general application abroad rather than in France. It is only necessary to cast a glance at the statistics to be convinced of this. From the date of the introduction of the Pasteurian vaccinations in 1884 up to the 1st January, 1900, there had been vaccinated in France in all 428,746 pigs, whilst abroad, where the vaccinations were introduced some years later, the number of pigs vaccinated was 4,819,387. Of this number the great majority (4,194,191) had been treated in Hungary. The losses amongst the vaccinated animals were insignificant (1·68%) when compared with an average mortality of 20% amongst unvaccinated pigs.
This limited extension of the vaccination of pigs in France arises from various causes. In many countries the breeding is on too small a scale to allow of the intervention of the veterinarian and of the expenses which the vaccinations involve. On the other hand, it cannot be denied that the Pasteurian method presents certain drawbacks in practice. The living, although attenuated, bacilli introduced may sometimes serve as centres of infection, especially in cases, rare no doubt, where the vaccinated animal contracts a chronic form of the disease. The Pasteurian vaccines must, therefore, be avoided in districts where the erysipelas has not yet appeared. Their application in countries already infected presents the further drawback that the immunity requires for its establishment a fairly long time, sufficiently long to permit the micro-organism to kill a large number of pigs before the vaccines have conferred any immunity upon them.
It is natural that, under such conditions, an attempt has been made to replace the Pasteurian method by some other method less risky. Hence, since the discovery of the principle of sero-therapy several investigators have sought to apply it to swine erysipelas. Emmerich and Mastbaum[792] were the first to demonstrate that the blood of rabbits, immunised with the bacilli of this disease, acquire a very marked protective power. They have even attempted to construct from the results of their researches methods which might be applied practically. It is especially however to Lorenz[793], a Darmstadt veterinarian, that we owe the first practical application of this method. He prepared protective serums by injecting erysipelas bacilli into rabbits and pigs, and demonstrated that the inoculation of these serums, when combined with that of the living bacilli, conferred upon pigs a sufficient immunity and one that was set up immediately after the introduction of the serum. According to Lorenz’s method it is first necessary to give a protective injection of serum; some days (3–5) afterwards this is followed by an inoculation of living bacilli coming from the attenuated erysipelas known in Germany under the name of “Backsteinblattern.” About two weeks later a further injection of the same bacilli, but in double quantity, is given. This method, therefore, involves three vaccinal injections as against two in the Pasteurian method. It is consequently dearer than the latter, but, as it presents certain undeniable advantages, an attempt was made to introduce it into veterinary practice. But being much more complicated endeavours were made to simplify it. Voges and Schütz, by methods which have remained secret, soon obtained a more active serum, and finally Leclainche[794] of Toulouse, after demonstrating that the horse is the best animal for the production of a very active serum, succeeded in devising a method of vaccination as simple as it was effective. He gave to it the name of “serum-vaccinations.” The first inoculation is made with a mixture of specific serum and a culture of living and virulent bacilli. This inoculation is well borne by all pigs and may be made without any regard to the age of the animal. The immunity is set up immediately after the injection of the mixture, but it is not sufficiently durable for the requirements of practice. For this reason Leclainche followed up the first injection by a second, which is made ten to twelve days later and consists of an inoculation of half a cubic centimetre of pure virus. This new method had the special advantage of arresting, almost immediately, the mortality in an infected piggery and of eliminating the chronic cases that are sometimes observed after the Pasteurian vaccinations.
Leclainche[795] has already applied his method of serum-vaccinations to more than five million pigs of all ages. “It has been found to be constant in its effect and absolutely innocuous,” and “not a single case of erysipelas has been met with in pigs that had received the two vaccines,” and Leclainche hopes that his method will soon come into general practice, and that it will be utilised in all cases where the Pasteurian method is found to be insufficient.
As the basis of all the new methods for vaccinating pigs against erysipelas is the preparation of serums capable of preventing the pathogenic effect of the bacilli, the question of the determination of the protective power of these serums comes to be one of considerable importance. At first one was satisfied with certain approximate estimations, but later the necessity was felt of having a more exact measurement. Leclainche is persuaded that of all the laboratory animals capable of being used for these experiments the pigeon is the only one that can usefully fulfil this rôle; very susceptible to the passage virus, it is killed by the bacillus after a regular incubation and invasion period, and the chronic form of the erysipelas, so troublesome in the rabbit and even in the pig, is met with in the pigeon in very exceptional cases only. Leclainche commenced his experiments by inoculating into the pectoral muscles of the pigeon mixtures of serum and virulent cultures. The pigeon received 1 c.c. of a culture of a passage virus mixed with variable quantities of serum. The serum is ready for use in the vaccination of pigs when the pigeons resist the injection of a mixture of ½ a c.c. of serum with 1 c.c. of a virus which kills the control pigeons in 60 to 72 hours.
At the Frankfort Institute of Experimental Therapeutics another method of testing devised by Marx[796] is used. In it injections, below the skin of a series of grey mice, are made of progressively increasing doses of the serum the strength of which it is desired to determine. Twenty-four hours later a virulent culture of the bacillus of swine erysipelas is introduced into the peritoneal cavity of the same mice. The virus is so chosen that the control mice die in about 72 hours. Marx finds that this method gives results which are much more constant and exact than any other; this opinion is confirmed at Höchst, the largest factory of serums in Germany.
VIII. Vaccinations against bovine pleuropneumonia. This infective disease is one of the most dreaded scourges of bovine animals. Very contagious, it has spread from central Europe not only into all the other countries of the European continent, but into Africa, America, and almost every quarter of the globe. The virus of this disease was discovered in the serous exudation of hepatised lungs long before the microbiological period of the Medical Sciences had begun.
Dr Willems of Harselt, who made an experimental investigation, remarkable for the time at which it was carried out (more than half a century ago), demonstrated at once the great virulence of the pulmonary serous fluid; he found also that the effects of the inoculation of the virus varied much according to the seat of inoculation. When made into the trunk, the neck, or the shoulders, the inoculations are usually fatal; at the periphery, the lower part of the limbs, at the extremity of the ears or of the tail, the inoculation ordinarily produces merely an inflammatory tumefaction of small extent, which is absorbed in a few weeks; after this the animal is refractory to the natural disease. Willems concluded from this that we may vaccinate against pleuropneumonia by inoculating the virulent serous fluid of the lung into the tail. Willems’ method of inoculation became a part of current practice 50 years ago.
For the carrying out of a large number of vaccinations it is necessary to have at one’s disposal an adequate quantity of virus; it was therefore to meet this requirement that researches were first carried out. The serous fluid was withdrawn from the hepatised lungs of animals that had succumbed to the disease and was inoculated into normal Bovidae as soon as possible, so as to avoid contamination of the fluid. In fact this pulmonary serous fluid often contains foreign germs capable of multiplying rapidly so that it putrefies very quickly. Pasteur showed that it was possible to remedy these drawbacks by a very simple method by which he could obtain a large quantity of rigorously pure virus. All that is necessary is to inoculate a little of the pleuropneumonic virus below the skin of a weaned calf, behind the shoulder. At the seat of inoculation there is an abundant exudation of virulent serous fluid into the cellular tissue, from which we are enabled to collect large quantities of pure virus.
In some countries, as in Germany and in Australia, institutions have been founded for the production by this method of the virulent serous fluid necessary for these inoculations.
The virus should be inoculated into the tip of the tail of animals that it is desired to immunise, because the temperature in this situation is relatively low and the connective tissue is dense and not very abundant. The inoculation is made with a lancet or a Pravaz syringe. The vaccination is generally borne well, in spite of the reaction phenomena which are manifested about two weeks after the introduction of the virus. At that time a febrile condition is set up and a swelling manifests itself at the point of inoculation, which, however, soon retrogresses and then disappears.
The immunity conferred by Willems’ method is substantial and lasting (for one or two years and even longer); this explains its great success in the hands of breeders and veterinarians. Accidents following its use are rare, and the mortality does not exceed 1 per cent.
In spite of all these advantages a new method was still desirable, a method which would allow of the preparation of large quantities of virus of a suitable and uniform activity under conditions of irreproachable purity. Thanks to the discovery of the micro-organism of pleuropneumonia which we owe to Nocard and Roux[797] this object has been achieved. With the collaboration of Borrel, Salimbeni, and Dujardin-Beaumetz, they succeeded in demonstrating and isolating this micro-organism, the smallest of all known living organisms. The first steps in these researches were very laborious, but later the organism of pleuropneumonia was cultivated on fluid and solid media: Martin’s broth (prepared with pigs’ stomachs) or agar with the addition of a certain quantity (about 5%) of fresh ox serum. The serum-broth, sown with pure pneumonic serous fluid, gives only a moderate growth, which becomes only slightly turbid and contains micro-organisms so small that it is impossible to distinguish them individually. They can be made out only when massed together in irregular clumps. The minuteness of this micro-organism is evidenced by the ease with which it passes through a Berkefeld filter, and even through certain Chamberland candles (F). This feature enables us to obtain the pure virus easily, a fact very important in connection with the isolation of the micro-organism.
Once in possession of pure cultures of the micro-organism of pleuropneumonia, Nocard and Roux attempted to make use of it in practical vaccination. They showed that the organism separated by them is capable of producing typical pleuropneumonia when it is inoculated into the appropriate regions of the body of bovine animals. But when inoculated subcutaneously or into the skin of the tail, it produces merely a mild and transient disease which confers an immunity quite as effectual as that set up by the inoculation of the virulent serous fluid. It may be readily understood that, under these conditions, pure cultures may be much more serviceably employed in the practice of vaccination than can Willems’ virus from the fact that it is easy to obtain large quantities of absolutely pure cultures. It is easy to predict that the new method will soon replace the old one, very great as are the services the latter has rendered to agriculture. Up to the present, vaccinations with pure cultures have been made in several districts in France with very favourable results. The Pasteur Institute and the Veterinary School at Alfort have already distributed to veterinary surgeons more than 5,000 vaccinal doses of culture; the protective action of these inoculations has been at least equal to that of the inoculations by Willems’ method and the resulting accidents have been reduced in the proportion of 20 to 1[798].
The serum of animals hyperimmunised against pleuropneumonia possesses a very distinct protective action, but too little marked and of too short duration to be of any use in practice; it has also a curative action arresting the invading march of a pleuropneumonic congestion; but here it is necessary to intervene early, before the appearance of fever, and to inject large quantities of serum.
The inoculation of a mixture of virus and serum produces no congestion; but it does not confer any immunity; the animal remains just as susceptible as the control to the inoculation of the pure virus.
IX. Vaccinations against typhoid fever. In the preceding sections I have treated more especially of the vaccination of domestic animals against several infective diseases. The information collected on this subject is marked by its great exactness, as it is easy to apply to animals the most rigorous experimental method. In the case of the human subject this is not such an easy matter. As it is impossible to submit him to experimental proof we are obliged to be satisfied with observation, controlled by statistical data. The experience of more than 100 years has, however, been sufficient to demonstrate the great utility of vaccinations against small-pox with the virus of cow-pox which is innocuous for the human subject. In the case of antirabic vaccinations we have to deal with injections into the human subject, first of weakened viruses and then of virulent viruses. Here, however, it is a question of the preservation of the already infected human organism, which, very often, only comes under treatment during the incubation stage of rabies. One can readily understand the hesitation to inoculate even weakened viruses into the human subject, especially when we are not dealing with altogether exceptional cases such as we have in the protection against rabies. We have, therefore, but few examples in which the methods of vaccination by micro-organisms have been applied to man. Such injections were first tried by Ferran[799] against Asiatic cholera. Having succeeded in vaccinating guinea-pigs against experimental cholera septicaemia, the Spanish investigator attempted to inoculate cholera vibrios into the subcutaneous tissue of man, hoping thus to vaccinate him against true cholera. In this way he was able to demonstrate that the subcutaneous injection of living vibrios never sets up symptoms of cholera. The injection is followed by a general reaction in the form of fever, pains in the back and inflammation at the point of inoculation, in a word, transient phenomena of little gravity. Encouraged by these initial results Ferran, profiting by the outbreak of cholera in the province of Valentia, injected into more than 20,000 persons living cultures of Koch’s vibrio. The results published by him did not, however, furnish any real proof of the possibility of conferring immunity against intestinal cholera by means of subcutaneous injections. Later Haffkine[800] modified Ferran’s primitive method somewhat, and instead of living vibrios he injected vibrionic cultures killed by heat or by antiseptics. During the cholera epidemic of 1892 and 1893 he tried the inoculation of these killed vibrios into man, with the object of vaccinating against Asiatic cholera. Later he went to Calcutta in order to try his method on a large scale. He was there enabled to inoculate a great number of persons, and the statistics which he collected appeared to him to be favourable.
But studies on the pathogenesis of Asiatic cholera shook the foundations of Ferran’s method. The injections of vibrios, living or killed, were found quite capable of vaccinating animals against vibrionic peritonitis and septicaemia, but they appear to exert no influence whatever against poisoning by the cholera toxin. When it had been learnt how to set up true intestinal cholera in young rabbits Ferran’s and other similar methods of vaccination were used in vain to prevent the incidence of this disease, which is very similar to Asiatic cholera of man. An experiment[801] made at the Pasteur Institute in Paris upon two persons vaccinated by Haffkine, showed that they were not protected against the choleriform diarrhoea set up by the ingestion of the cholera vibrios. A third person, who had never been “vaccinated” and who served as “control,” after the ingestion of the same cholera culture, behaved exactly as did the other two.
From all these data the conclusion was drawn that in order to prevent intestinal cholera it is necessary to use not cultures of vibrios, living or dead, but antitoxic serums. In fact, the majority of young rabbits vaccinated with these serums and afterwards submitted to infection by the cholera virus through the mouth were found to be vaccinated against intestinal cholera. It has not been possible, as yet, to apply this method to man, hence we are unable to give a decided opinion. Moreover, as the methods based on Ferran’s principle have now been abandoned I have not deemed it necessary to devote a special section to anticholera vaccinations. I could not, however, pass it by in silence, since the attempts to vaccinate man against cholera have led to the trial of a similar method against typhoid fever.
Pfeiffer and Kolle[802] were the first to inoculate man with typhoid coccobacilli sterilised by heat. They observed that these injections caused fever, pretty violent pains in the back accompanied by vertigo, shivering and pain at the point of inoculation, without, however, being in any way serious to health. At the same time they found that the blood serum of inoculated persons acquired a very marked protective power (for guinea-pigs injected into the peritoneal cavity with lethal doses of typhoid cultures) quite comparable to the properties discovered by them in the serum of persons who had recovered from typhoid fever. Pfeiffer and Kolle believed that they thus had a proof of the refractory condition of the individuals whom they had submitted to these injections.
These experiments were continued by Wright, Professor of Pathology at Netley, and it is owing to his unwearied efforts that science finds herself in possession of very important evidence on the subject of protective inoculations against typhoid fever in man. According to a verbal communication made to me by Wright, he has up to the present distributed more than 300,000 doses of his antityphoid vaccine. This vaccine he prepared in the following way[803]. The typhoid coccobacillus is sown in carefully neutralised broth containing 1% of peptone. The flasks of culture are kept in the incubator at about 37° C. for two or three weeks, after which their contents are transferred to large flasks in order to be submitted to a temperature of 60° C. This temperature is quite sufficient to kill all the coccobacilli, but for greater surety Wright added to his cultures one-tenth of their volume of a 5% solution of carbolic acid or of lysol. The vaccine, thus prepared, is examined as to its toxicity for the guinea-pig by means of subcutaneous injections. Wright injects into man a dose of vaccine which is sufficient to kill 100 grammes of guinea-pig (of the weight of 250 to 300 grammes). This dose often amounts to half a cubic centimetre, but it may have to be increased to 1 c.c. and even 1·5 c.c.
The inoculations are made below the skin of the flank or in the shoulder. They are followed by a rise of temperature which commences as early as two or three hours after the injection. This fever is accompanied by pains in the back, nausea, and want of appetite. There may even be collapse; this led Wright to keep his patient in bed for some time after the vaccinal injection. Besides this reaction, there occurs, at the seat of inoculation, a swelling and redness, accompanied by pain; as a rule all these symptoms have disappeared by the end of 48 hours.
Wright convinced himself that the blood serum of individuals treated by his vaccine, at the end of a certain time acquires the property of agglutinating typhoid coccobacilli in a variable, but usually very marked degree. He even thought that this property might up to a certain point serve as the measure of the immunity acquired against typhoid fever. His own researches, however, showed him that this supposition could not be maintained, and that the agglutinative power, varying greatly in strength, might sometimes be absent where the immunity could not be denied. On the other hand, he clearly showed, especially by the experiments with serum collected at the period which precedes the relapses, that the agglutinative property might be highly developed, in spite of the absence of immunity. Wright then set himself to study the bactericidal property of the serum of individuals who had been injected with his vaccine. He devised a very ingenious method of gaining with a minimum loss of time some idea of the fluctuations of this power of the body fluids to kill the typhoid coccobacillus. In the first place he demonstrated that the bactericidal property is not at all parallel to the agglutinative power, and this has further confirmed him in his opinion that there may be no direct relation between it and acquired immunity. He has found further that the power of the blood serum to destroy the typhoid coccobacillus is very variable in persons vaccinated by his method. After injections of large quantities of these killed bacilli this power may even be diminished for a very long period. On the other hand, medium or small doses of the vaccine first set up a negative stage, during which the bactericidal property is very feeble, and later they bring about an increase of this property, often very marked. Wright does not think that the bactericidal power can serve as the measure of the immunity acquired by the vaccinated individuals, but he hopes that some day a method may be found suitable for the examination of the blood which will give us information as to the degree of immunity conferred by the antityphoid vaccination. For the present the only basis upon which we can form any opinion on this subject is furnished by statistics. Now we know that it is often very difficult to collect data that are sufficiently exact. Hence during the war in South Africa, where one-fifth of the English troops, that is to say about 50,000 persons, were submitted to vaccinations by Wright’s method, it is only in certain cases that the statistical information can be utilised. Many of the patients attacked by slight fevers are omitted from the statistics, because from the absence of a precise diagnosis it is not known whether they should come under the category of typhoid patients or not. In other cases the secondary complications divert the attention of the doctors and prevent the registration of a proper diagnosis.
Of the data collected amongst the English troops in South Africa, Wright considers that those which were collected during the siege of Ladysmith were the most exact, on account of the facility with which it was possible to study and register all the cases of typhoid fever under these conditions of complete isolation. Now it has been recognised that, amongst the vaccinated soldiers and officers, there occurred scarcely one-eighth as many cases of typhoid fever as occurred amongst the unvaccinated (1,499 cases in 10,529 unvaccinated, and 35 cases in 1,705 vaccinated). The mortality amongst the vaccinated was also very much lower. The difference to the credit of the vaccinations should in reality be even greater, for amongst the unvaccinated are counted many persons who having already had an attack of typhoid fever were not submitted to vaccination.
The testimony of the majority of the medical men who followed the results of Wright’s method closely is also favourable to the vaccinations. Thus Henry Cayley[804] reports that the staff of a Scotch Hospital of the Red Cross, almost all of whom (57 persons out of 61) had received two vaccinal inoculations, escaped typhoid fever, in spite of the numerous opportunities afforded for the contraction of the disease. This very favourable example is also instructive in that it testifies to the value of two consecutive vaccinations. In many other cases where one has had to be satisfied with a single protective inoculation the results were less brilliant. According to Howard Tooth, who made his observations at Bloemfontein, the vaccinations according to Wright’s method must be regarded as very useful.
Outside South Africa this method has been employed on a fairly large number of persons in British India, in Egypt, and in Cyprus. According to the earlier statements from India the incidence amongst the vaccinated persons was one-third that of the unvaccinated. The most recent statistics[805] show still more favourable results. Thus at Meerut the incidence amongst vaccinated persons from Oct. 1899 to Oct. 1900 was one-eleventh that of the unvaccinated (2 cases of typhoid fever in 360 vaccinated, and 11 cases of the same disease in 179 unvaccinated): the mortality (one case amongst the former, six amongst the latter) was less than one-twelfth that of the unvaccinated.
In Egypt and in Cyprus according to the statistics communicated to Dr Wright[806] by Col. Fawcett these vaccinations have given even better results. In 2,669 unvaccinated persons there occurred 68 cases of typhoid fever with 10 deaths, whilst amongst the 720 vaccinated there was only a single case of this disease, this single case succumbing. Here, however, we have to do with a patient who must have received the vaccinal inoculation during the period of incubation, the disease breaking out soon after the vaccination. This would represent in all the cases a morbidity only one-seventeenth as intense amongst the vaccinated.
A few isolated voices only have not pronounced in favour of the antityphoid vaccinations and their opinion is formulated in a very undecided fashion. Amongst the most important of these adversaries, if indeed we may term them such, must be cited Washbourn[807], on account of his experience in microbiology. Attached as a doctor to the Yeomanry Hospital at Deelfontein in South Africa, he witnessed many cases of typhoid fever and was greatly struck by the death of two persons amongst the vaccinated patients. But he himself confesses that it is as yet premature to judge Wright’s method, and in support of his sceptical attitude does not offer any other satisfactory observation.
Outside the English colonies vaccinations against typhoid fever have been tried in Russia by Wyssokowitch[808]. He inoculated 235 soldiers of a regiment encamped at Kiew, amongst whom an epidemic of typhoid fever had broken out. The vaccinations were carried out by means of cultures killed with carbolic acid. We are unable to judge of the efficacy of the method because the number of persons vaccinated was too small and the epidemic too limited. It may be noted, however, that amongst these individuals not one took typhoid fever, whilst amongst the unvaccinated three cases of the disease were registered.
The antityphoid vaccinations have as yet only a very short history, and it is, perhaps, premature to express any decided opinion on the matter. We may, however, consider the results already obtained as offering encouragement to continue our experiments. Everything, indeed, tends to a recognition of the utility of vaccinations by means of killed typhoid cultures. The statistics are as a rule good; the danger from the protective inoculation is nil or quite trifling. With the exception of the discomfort of which we have spoken and which is transitory, no untoward result has ever been observed.
To all this must be added the fact that from the point of view of the pathogenesis of typhoid fever, all the probabilities point in favour of the vaccinations. Whilst in Asiatic cholera we have to deal with an intoxication, from the alimentary canal, an intoxication set up by vibrionic products, against which the subcutaneous inoculation of micro-organisms can not be effective, in typhoid fever we have to do with a real infection. The micro-organism, although developed at first in the small intestine, becomes generalised throughout the system. Thanks to improved methods it can always, or almost always, be found in the blood of the patient, and its constant localisation in the spleen furnishes a real evidence of this. Under these conditions it is quite natural to suppose that everything which is able to prevent the penetration of the typhoid coccobacillus into the blood and the internal organs ought at the same time to contribute to the protection of the individual.
We are fully aware that science has not yet said its final word upon this question. We are coming more and more to the conclusion that it is necessary to make two injections instead of one. It is possible that we may have recourse to certain improvements of the method by combining with it the injections of antityphoid serums as a protective measure. The near future will doubtless bring us the solution of these very important questions.
X. Vaccinations against human plague. Plague, which for so long was looked upon as the greatest scourge of humanity, has until recently remained almost unknown from the scientific point of view. But from the moment that it became possible to apply to its study the immense advances realised by microbiology the thick veil which had hidden its nature fell at a single stroke and science found itself in possession of effective means of fighting against it. Amongst these means one of the most important is protective vaccination.
When the last pandemic of plague broke out in Bombay and in the East Indies in general, Haffkine was there engaged in applying his method of vaccination against Asiatic cholera of which we have spoken in the preceding section. Well acquainted with the results of the bacteriological researches made on bubonic plague by Kitasato, and especially by Yersin, he, in 1896, began to study this disease. After the discovery made by Yersin, Borrel, and Calmette[809], who showed that animals susceptible to human plague could be easily vaccinated against the micro-organism which gives rise to it, Haffkine[810] endeavoured to find a practical method for the vaccination of man. He set up a laboratory at Bombay and, after some preliminary experiments on rabbits, he commenced to inject human beings with pure cultures of the plague coccobacillus. From 1897 up to the present he was able to vaccinate a very large number of individuals, and the results obtained have encouraged him to continue the application of his method. The principle of this method is that which had guided him in the preparation of anticholera vaccines and which is used for the vaccines against typhoid fever. It consists in the employment of pure cultures of the specific organism killed by heat. The cultures are grown in large flasks containing peptonised broth and sown with a small quantity of the plague coccobacilli. A little sterile butter or cocoanut oil is poured on the surface of the fluid. Under these conditions the organism grows abundantly and produces growths which hang down into the fluid, reminding us of the stalactites in a grotto. This mode of development forms one of the most typical characters of the micro-organism of human plague. The culture flasks are kept at a temperature of about 30° C. for five to six weeks, at the end of which period a large number of the bodies of the micro-organisms have fallen to the bottom of the flask, allowing much of their toxic contents to escape. The fatty layer on the surface favours a surface development of the coccobacilli, the number of micro-organisms in a flask being thus greatly increased.
After growing for 35 to 42 days under these conditions the cultures are heated at 65°–70° C. for from one to three hours with the object of killing all the micro-organisms and so rendering their injection innocuous. To make sure of the effectiveness of this heating care is taken to remove a small portion of the fluid and to sow it in a suitable medium. Should this medium remain sterile the vaccine may be used. Into adult men it is injected in a dose of 3 c.c., whilst women, children, and adolescents receive 2–2·5 c.c., into the subcutaneous tissue.
Some hours after the injection of the vaccine the temperature rises above normal, reaching 38°·5 to 39° C., and sometimes even 40°–40°·5 C. This febrile condition lasts from 15 to 48 hours. It is soon accompanied by pain, redness, and swelling at the point of inoculation. These symptoms persist for from three to five days. The malaise which follows the vaccinations is sometimes very uncomfortable or even painful, but never serious. Only in exceptional cases is the formation of abscesses observed, and this is due, undoubtedly, to contamination of the vaccines by foreign micro-organisms. The English Commission sent to India to study plague found other micro-organisms than the plague coccobacilli fairly frequently in the vaccine culture flasks, but, with very rare exceptions, these micro-organisms were found to be innocuous. By rigorously following the rules to be observed in making pure cultures it should not be difficult to avoid this complication.
Haffkine used every effort to induce his patients to be vaccinated a second time, being justly persuaded that two injections are capable of ensuring a more certain and more stable immunity than is a single injection.
From what moment immunity may be considered to be acquired has been a matter for great discussion. From very numerous experiments upon animals of various species, as well as many observations on man, it is now agreed that a period of several days (5–8) from the injection of the vaccine is required before immunity is manifested. It is for this reason that cases of plague which have broken out before this period has elapsed cannot be looked upon as contraindicating the efficacy of the method.
A large amount of evidence, coming from persons who have made their observations on the spot, is almost unanimous in endorsing the fact that Haffkine’s vaccination protects man against plague. It is often difficult to compile exact statistics in surroundings where so many factors contribute to deceive even the careful observer. In spite of this a certain amount of evidence has been collected which may be accepted as affording us fairly satisfactory information. One of the best groups of statistics was that collected at Damaun, a Portuguese possession in India, into which plague was imported from Bombay in 1897, and where a large number of vaccinations were carried out. From the report of Haffkine and Lyons[811], in a population of 8230 persons, rather more than one-fourth (2197) were vaccinated, the greater majority (6033) remaining uninoculated. Amongst the former only 36 died from plague, which corresponds to 1·6 per cent.; whilst amongst the unvaccinated persons the disease carried off 1482 persons or 24·6 per cent. Vaccination, therefore, according to these statistics, must have brought down the mortality to one-fifteenth. The German Commission[812], two members of which, Koch and Gaffky, went to Damaun to be present at the vaccinations and to observe their efficacy, pronounced in favour of Haffkine’s method. The English Commission[813] made reservations and criticised the statistics of Haffkine and Lyons (who amongst others attribute all the cases of deaths that occurred amongst the unvaccinated to plague), but in the end this Commission also recognised the utility of the vaccinations at Damaun.
The data collected with regard to the vaccinations at Undhera, Hubli, and several other places in British India confirm the results obtained at Damaun. The statistics collected at these localities are certainly open to criticism, but the result as a whole is none the less encouraging as regards this method of vaccination. According to the conclusions of the English Commission the “inoculations had a considerable effect in warding off plague attacks from the inoculated.... The protection afforded by inoculation seems, however, never to be absolute[814].” We do not, as yet, know the duration of the immunity produced by Haffkine’s vaccinations; it cannot be very long to judge from the experiments on animals, but it may last for several weeks, probably even for months.
The vaccinations by killed cultures may be especially useful when it is a question of limiting the extension of an epidemic that is already established. The ease with which the vaccine can be prepared renders it possible to obtain very large quantities of it in a short time, with which it is possible to immunise the entire population of towns or districts. But, as the immunity by this method requires several days for its development and as the injections of micro-organisms, even when killed, may be very injurious during the incubation period of plague or immediately before the infection, it is necessary to limit the vaccinations to persons who are not in intimate contact with the sick, or who are, from the beginning, exposed to infection[815].