In adopting the above heading for this article it has been considered that a change from the more widely used term "Contagious Abortion" is very desirable. It is well known, of course, that the farmer always refers to this disease as "Contagious Abortion" but it is now thought the name Bang's Disease is preferable for the following reasons:—
1. "Contagious Abortion," while emphasising the fact that the disease is contagious and indicating that the chief symptom is abortion of the foetus does not give a true idea of the nature of the complaint to the layman.
2. As the word "abortion occurs in the name of the disease, the farmer is naturally induced to think that if a cow aborts she therefore has "contagious abortion" while if a cow does not abort she is not infected. This belief, of course, we know to be wrong, but it is widespread and one which has lead many farmers to doubt the reliability of the agglutination test.
Probably every stock inspector who has worked in a dairying district has experienced at least one case where upon sending sera to the laboratory for agglutination test the farmer has doubted the results of the test saying "Well that's funny, this cow aborted three months ago and you say she is not infected while this cow has never aborted and you say she is infected."
3. The name "Contagious Abortion" tends to convey to the farmer that abortion of the calf is the only loss occasioned by the disease. This is also false for we know that it has been determined that an infected herd is about 20% below a clean herd in all round production.
This fact should be brought home more forcibly to our farmers and the present name does nothing to do so.
4. It is considered advisable to educate our farmers to a proper appreciation of the losses caused by this disease apart altogether from the loss of calves and probably the best way to commence such a campaign would be to change the popular name of the disease. If the farmer can be taught to speak of this disease as something more than mere abortion then he will commence to think of it as something more than the lass of calves whether occasional or frequent.
The stock inspector is in the best position to act as spear-head in the education of the farmer and it is felt that if he refers to this disease as causing losses in addition to abortion then he will find the farmer following suit. If he further explains to the farmer his reasons for the change of name then he will induce the farmer to think of this disease as occasioning more loss than is generally known at present and so bring it into its proper perspective.
There is no doubt that the disease is regarded far too lightly by the majority of our dairy farmers who do not think anything of a few abortions each year—probably because of ignorance of the more insidious losses occasioned.
If we discard the term "Contagious Abortion," what shall we accept as a common name which will not appear too technical for use by the farmer.
"Bang's Disease of cattle," the name by which the disease is popularly known in England and America appears perhaps a little technical but still well within the range of average pronunciation and understanding and such a term will serve two purposes.
1. It will bring home to the farmer that the disease is a definite well recognised disease whose cause is known it will not make the symptom of abortion needlessly exaggerated and it will make much easier the education of the farmer to an appreciation of the fact that BruceIla infection is much more than an infection of the uterus with consequent abortion.
2. It will indicate that cattle are only one of the species of animals which this organism infects. Thus it will not be so difficult to educate the farmer to the fact that men, horses, cattle, pigs, dogs, goats and sheep are susceptible and may become a prey to this insidious infection.
It is accordingly suggested for your earnest consideration that you should, whenever an opportunity presents itself, attempt to educate the farmer to call this disease "Bang's Disease of Cattle," and discard the term "Contagious Abortion" and in doing so impress on him that the disease not only causes loss by causing abortions but in many other ways.
As examples of losses which the farmer may not readily associate with BruceIla infection we may cite sterility, weak stunted calves many of which die in the first few weeks of life and are usually very susceptible to juvenile diseases, diminished milk yield, diminished butter fat yield, as well as loss of calves and the last example is placed in its position deliberately.
If the farmer has been educated to view this disease in its proper perspective he will assuredly wish to rid himself of this scourge of the Dairy Industry, and will ask how this may best be effected.
Viewing all the available evidence, there is no doubt that the best method of control which we have at our disposal at present is the complete eradication of the disease by testing all cattle over the age of six months on the farm and culling all reactors from the herd.
Now, at the outset, let me make clear that this is no easy task. The stock inspector or farmer who approaches eradication of Bang's Disease from a herd lightheartedly and without serious consideration of the past history, and present status of the herd, the facilities of the farm and, as far as the stock inspector is concerned, the intelligence and willingness of the owner to co-operate, is doomed to a long hard understanding, costly and disappointing.
Brucella infection can only be eradicated by the closest possible intelligent co-operation between the field officer and the farmer and failure of the scheme for eradication is certain should either of agents fail.
Before any decision is reached as to the eradication of Bang's Disease from any one farm, the most thorough investigation of the individual status of that herd and farm and particularly the breeding history of the herd should be made and the decision to proceed or wait some time should be based on this investigation.
For instance it is now considered very inadvisable to proceed with the eradication of the disease from a herd where abortions are occurring frequently and the infection is spreading actively. An owner with such a herd should be advised, in the light of present knowledge, to wait for some time until the disease has assumed its quiescent form within the herd before commencing eradication.
If he wishes to proceed despite this advice, he should be well informed that the task will be long and costly and the length of time required will be directly proportional to the number of cattle he finds he is compelled to introduce to keep up the production of his herd.
This latter statement is true of any herd. If possible, an effort should be made by inspectors to persuade the owner to refrain from introducing any cattle from outside sources (i.e. animals from known negative herds) until such time as his own farm and herd have been freed of the disease. It has been found in America that one of the most potent causes of prolonging the time taken to eradicate the disease from a herd was the introduction of cattle from negative herds. These cattle, being very susceptible to the disease, tend to become infected readily, and one finds the disease persisting not so much in the original herd was in the introduced highly susceptible cattle. Where an owner finds that he must introduce cattle from outside sources he should be warned of the probable result. It is, of course, needless to say that if any introductions are made they must come from known negative herds.
Proper facilities for handling the herd should exist. Bleeding of all animals over six months of age should take place every 30 days and so adequate facilities for handling the cattle should be available. It will be found that bleeding from the jugular vein is much more rapid, much easier and much more satisfactory than other methods and results in better serum samples and cleaner cattle following the operation. Therefore, I would urge the adoption of this method to all field officers and suggest that when a farmer signifies his intention of commencing eradication he be strongly advised to erect a special crush at a suitable location in his yards for this purpose. If the owner is made to realise that all his cattle must be bled every 30 days for such time as required to obtain two clean tests—a period of at least three months—and if he is also advised that jugular bleeding will leave his cattle and surroundings much cleaner than other methods, it will probably not be hard to persuade him to erect a special crush as suggested. Such a crush will pay for itself very quickly on any farm in the increased ease with which cattle can be handled and bled.
The habit of buying cattle subject to one agglutination test is another practice which should be condemned. This should never be allowed in any herd where eradication is in progress for one test is not enough to ensure freedom from the disease and may be very misleading. If an animal has just become infected she will not give a positive reaction for some time. At present, the weight of evidence is that this "incubation period" varies from one week to one month, but at Minnesota one cow has been encountered which did not give a definite positive reaction for 72 days following the date of infection. This cow, however, did give several "suspicious reactions" to the test in the interval. Even with massive doses injected into the jugular vein, this lag of about one week is noted so that one isolated test is not sufficient. If an animal is being bought from an infected herd subject to test, she should be held in isolation on the property of the purchaser—and this means rigid and complete isolation—for at least 30 days and retested at the end of that time. In these cases all herds which are not known to be accredited "abortion-free herds" should be considered as infected herds.
The progress of the disease in the herd should be carefully studied. At the first general test of the herd the percentage of infection will be apparent and an attempt should be made to corelate past abortions with positive reactions. If it is found that many cattle whose reactions to the first herd test is negative have aborted, it can be assumed that there is probably some factor other than Bang's Disease operating in the herd, and the owner should be advised accordingly. In such a herd the eradication of Bang's Disease will not remedy the abortion rate and the cause of the abortions should be found and, if possible, remedied.
If the initial test shows a high percentage of infection in the herd (over 25%) the owner should be warned that eradication will not be easy, will take some time, and may be costly. He should be advised, if possible, to refrain from introducing any stock as replacements until such time as his herd is cleaned as experience has shown that the most common cause of persistence of disease in a herd is the constant introduction of cattle from negative herds.
Where the disease is obviously spreading rapidly through a herd as evidenced by a high incidence of the disease with many abortions, all the aborting cattle being reactors to the test, it may be well for the owner to wait until the disease has reached the quiescent state before eradication is commenced. In a herd of this nature, great care must be taken to isolate all "suspects" and it may be necessary, and would certainly be advisable, to bleed the cattle for test more often than every 30 days. In the United States it was found that many herds of this nature could only be cleaned up after prolonged testing at intervals of 14 days.
Thus, before eradication is commenced, the owner should have adequate facilities for the handling of the herd efficiently, and should be advised as to the probable ease or otherwise with which eradication may be effected. Care and judgment is necessary in giving the latter advice and one should always be guarded but, in cases where the incidence of the disease is high and the disease active, a special warning should be given and, if possible, the owner should be persuaded to postpone eradication until such time as the disease has become quiescent.
The suspicious reactor is a type of animal which gives great concern to the farmer, the field officer and the latoratory worker. What danger is she to the rest of the herd? Should she be culled, together with the reactors, or can she be left with the rest of the herd with safety? These and many other questions are continually being asked of this type of cow and it is now possible to give some definite information based on actual knowledge.
Firstly. the suspicious reactor should always be considered as dangerous. She should never be allowed to mix freely with the negative reactors in the herd and should always be kept in isolation. It is well known that the Australian farmer has a strong dislike for doing this. He will not readily agree to placing one cow in a separate isolation paddock away from the rest and holding her there for at least a month. This requires added attention apart from that given to the rest of the herd and he will frankly admit that "it is too much trouble."
It probably is a task but it is a part of the trouble to which he will be put in the eradication of the disease and should be looked at as such. He should be advised before he commences eradication that a small isolation paddock will be required for this purpose. Where the farmer will not or cannot isolate his suspicious animals until a definite diagnosis can be reached, he should be counselled to treat them as reactors or warned of the danger of leaving them with his herd. One far too frequently encounters cases where an inspector reports that an animal, suspicious to the previous test, has aborted on pasture with the negative herd before she could be retested. This could be prevented in every case by taking the trouble to isolate such suspicious reactors.
In a study of 1,000 cows which gave a suspicious reaction to one test and were retested, Dr Fitch of the University of Minnesota found that 77.4%, were negative to the second test, 12.4% became definite reactors and the remaining 10.2% were still suspicious. Some 67 of these animals went on to be tested five times. By this time some 83.6% were negative while an additional 4.5% became positive. Actually, of the 1,000 original suspects, some 12.4% were removed as reactors at the second test whereas by the end of the fifth test only an additional 4.2% had become positive. Thus, of any given number of suspicious reactors to one test, Dr. Pitch found that the majority (between 70% and 80%) will give negative reactions to the next test while of those animals which will become positive to test eventually about 66.6%, will be picked out by the same test.
With regard to those animals whose reactions remain suspicious, Dr. Pitch has kept many such in herds without any "breakdown" occurring. It is absolutely necessary to know the exact history of both the herd and the individual animal before any effort can be made to keep such animals with safety.
Some 30 odd animals in this category have been studied intensively by Miss Bishop of Dr. Pitch's staff and in no single case has she found any evidence of Brucella infection.
Dr. Fitch has also examined the histories of cattle which react to the test. In two studies, one on 1,000 animals and the other on 2,000 animals, he found that over 80% of reactors were negative to their previous test while only about 12% to 14% were "suspicious" to the previous test. This shows very clearly the danger of relying on a single agglutination test as evidence of freedom from disease and also shows that the reactor is seldom "suspicious" to the previous test.
In the United States of America it has been found that the majority of herds can be cleaned up with four or five tests. In those cases where eradication is prolonged beyond this number of tests, it is usually found that it requires a large number—10 to 15 tests to clean a herd. In these herds it is certain that some special factors, at present unknown, are operating and such herds demand special attention.
One cannot say whether American experience will be duplicated in this regard in Australia as our herds are larger than American herds and the American workers have found it is harder to eradicate the disease from large than from small herds. However, we do know that the disease proves very hard to eradicate from a small number of our herds and such herds must receive more careful attention than they have in the past. One thing to look for in such herds is the possibility of one or more cattle being of the "non-reacting infected cow" class. It has been found that a small number of animals, the exact percentage being at present unknown, will not react to the agglutination test although they are actually infected. The reason for this phenomenon is not known but it is an idiosyncracy of the individual cow. Such cattle will give a positive milk whey agglutination reaction however, and may be picked up by this test. Where such herds are encountered, therefore, it may be advisable in selected cases to take bulk milk samples from each individual cow for examination in the laboratory. Such action should not be taken before the advisability for it is discussed with the Director of Veterinary Research.
In the literature dealing with Bang's Disease, one at times finds statements which assume that the calf of a reactor may at times carry the microbe in its body from calfhood to maturity although it does not react to the test before it aborts. There is nothing in the literature to give any experimental evidence for this statement and it must be considered pure theory until such time as proof may be available. On the contrary the available evidence tends to show that the calf of the reactar does net carry the infection through to maturity.
All calves will react to the agglutination test while they are drinking infected milk, and calves of reactors commonly carry the microbe of Bang's Disease in their bodies at birth and for a short time afterwards. Within six months of weaning, however, the blood-serum of all calves will have gradually lost all power to agglutinate the microbe of Bang's Disease and they will all give negative reactions. If kept in disease free surroundings they will remain negative reactors and will carry their calves tn full term without showing any evidence of disease when examined bacteriologically at time of calving.
This has been shown by Dr. C. P. Fitch and Miss Licille M. Bishop of the University of Minnesota who have studied this aspect of Bang's Disease in over 30 cases of heifer calves born of reacting dams and reared in disease free surroundings. All remained negative to test and carried their calves to full term without evidence of disease.
Thus there is little likelihood of spread of the disease by calves of reactors carrying the infection from calfhood to maturity.
Much knowledge has yet to be gained on the ways in which Bang's Disease may spread from animal to animal and herd to herd. At Cornell University, New York, it was found that 11 cattle were held in an enclosed loose box with flies and infected material was placed in a position where the cattle could not possibly have access to it they still became infected, the flies being the probable vectors.
Also at the University of Minnesota, Miss Bishop has examined the bodies of a large number of the common brown rat for the presence there of the microbe of Bang's Disease with the result that only one carcase was found to be infected. Investigators in other countries have found higher percentages than the Minnesota workers and although mere infection of the rat does not prove that this animal is capable of spreading the disease from farm to farm. the possibility of such agents must be considered.
Miss Bishop has also examined the saliva of infected cattle for the presence of the microbe with negative results.
Several statements have occurred in the literature on Bang's Disease with regard to the possibility of an animal becoming infected early in pregnancy and not showing any indication of being infected until after she has aborted when she will give a positive reaction to the tests. Some authors have definitely stated that this may at times occur but no single case has been cited in the literature where the date of infection was known. It would be rather peculiar, if this did occur, that no single case of such phenomenon has to date occurred or been reported on any experiment with Bang's Disease and many thousands of cattle must have been exposed to infection in carefully controlled experiments throughout the world, during, say, the past 20 years.
Many American workers doubt this assumption and Dr. Donham, of the Ohio State University has commenced a long range experiment with the object of throwing light on this problem. Results to date indicate that cattle react to test within a reasonable period of exposure to infection.
Vaccination as a method of control of Bang's Disease has been investigated extensively in the United States of America. All methods of vaccination except that under trial at present have been discarded for various reasons but the present trial seems to hold out some hope of success.
This method consists of vaccinating calves before they reach the age of six months with a strain of the microbe of Bang's Disease which is of reduced virulence. The calves react to test for a variable period following vaccination but the majority are negative to test by the time they reach maturity. Experiments carried out in the United States show such vaccinated animals to have some degree of resistance to infection when carrying their first calves but little evidence is as yet available on second, third and fourth pregnancies. These trials at present in progress abroad are still in the experimental stage and though this method shows promise we should be very guarded in drawing conclusions as yet.
A culture of this strain was brought back to Australia and experiments will be carried out at the Veterinary Research Station, Glenfield, to test the vaccine under Australian conditions and until such time as this test is complete no vaccination will be practiced in the field. When considering vaccination as a method of control, we should always remember that no disease has so far been completely controlled by a vaccine, and so vaccination, though it may be very helpful in aiding control of Bang's Disease, especially in heavily infected herds, will never entirely replace the present method of eradication by testing and elimination of reactors.