JOHNE’S DISEASE.

New Zealand Journal of Agriculture, Volume 54, Issue 1, 20 January 1937, Page 1

JOHNE’S DISEASE.

E. H. Stephens, Veterinarian,

, Stratford, and Dudley A. Gill, District ive-stock Division, Wellington. '

Superintendent, Li-

Johne’s disease is a ‘slowly developing, chronic inflammation of the intestines which eventually causes the affected animal to scour uncontrollably, so that it- becomes greatly emaciated and dies of sheer exhaustion.

Sheep are occasionally infected with the disease, goats may contract it also, and it has been recorded in a herd of deer. It seems to be a disease to which any ruminant is more or less susceptible, although cattle are the only ones commonly affected. Dairy breeds are more commonly affected than beef breeds, but that is probably due to the strain of calving and milk-production lowering their powers of resistance, and also to the fact that beef cattle are slaughtered at a comparatively early age. It is considered that there is no difference in

the susceptibility of the different dairy breeds. .Naturally if one breed predominates in an infected country the cases will occur mainly in that breed. A point which requires stressing is that Johne’s disease spreads very slowly. Acute diseases, such as swine fever or foot-and-mouth disease, sweep through a herd in a few days, but that is far from being the case with Johne’s disease. Even on a badly infected farm it is seldom that more than three or four clinical cases — i.e., cases showing recognizable symptoms —occur in any one year. The Cause. Johne’s disease is caused by a microbe that is similar in many ways to the bacillus of tuberculosis. Especially does it resemble the type of tubercle bacillus that affects birds. Indeed for many years after the cause was first discovered by Professor Johne in Dresden in 1895, it was thought to be a peculiar form of intestinal tuberculosis and was called “ paratuberculous enteritis.” ‘ Although there is evidence to suggest that the disease was present in Europe at least 100 years ago, and there is no means of knowing how much longer it was in existence before that, it was only in 1895 that Johne first detected the causal organism in the bowel lesions. Even then there was no proof that this: microbe was really the cause, as Johne, and others who attempted it after him, were unable to grow it and consequently experimental work on the usual lines could not be undertaken. It was not until 1912 that Twort and Ingram found the means of growing this bacillus in the laboratory. The difficulty arose through the fact that Johne’s bacillus has very peculiar growth requirements and does not grow at all on any of the media commonly used for culturing micro-organisms. In addition to that, even when a suitable medium for growth was found, the bacillus grew so slowly that only after several weeks’ incubation was it sufficient to be detectable with the naked eye, whereas the majority of microbes give easily visible colonies in a few days at most. Only within the last three or four years have improved media been evolved which give a visible growth of Johne’s bacilli in a somewhat shorter time. ■ Then, too, it is possible with almost all diseases to study them by using small animals such' as rabbits, mice, or guinea pigs, but Johne’s disease cannot be transmitted regularly to any of. these species, and this- fact was, and still remains, a very serious obstacle in the way of research work. It is necessary to mention these facts so that it may be appreciated why our present knowledge of Johne’s disease has taken so long to acquire, and why even now that knowledge is far from complete. Symptoms. The earliest symptoms shown by an affected animal are a tendency to loose bloom and to have a harsh staring coat. There is nothing in this on which a diagnosis can be based, and many other diseases, of which tuberculosis is one of the commonest, produce similar early indications of their presence. But in a herd where Johne’s disease is known to occur these signs, manifested at a time when the feed conditions are such that the rest of the herd is thriving well, should always be regarded with suspicion.

. Later there is scouring and more rapid wasting. The diarrhoea is often intermittent at first, and the cow, after scouring and losing condition for a fortnight or so, apparently recovers and puts on flesh again only to have another attack of scouring a few weeks later. The intervals between attacks of . diarrhoea become. shorter, and finally persistent scouring sets in, quickly reducing the animal to a skeleton, and death from weakness and exhaustion puts an end to the case.

In other instances an animal may show no sign whatever till persistent scouring occurs, when it quickly wastes and may die in two or three weeks. This is fairly common just after calving in affected cows, and the rapidity with which some such cases will waste and die under the effects of the continuous scouring is remarkable. . In the more slowly developing type of case, with intermittent attacks of diarrhoea, there are two symptoms which, while they do not invariably appear, are useful aids to diagnosis. One of these is the

appearance of a dropsical swelling under, the throat and jaw and the other is a tendency to waste more markedly about the hindquarters, especially the thighs and buttocks, than in other parts of the body. Below are two photographs of a case which demonstrates these two points very clearly. The affected animal shows no sign of illness other than the wasting and diarrhoea. She is not feverish and continues to eat. Naturally her milk-yield falls away, and as a result of the diarrhoea and consequent loss of fluid from her body there is generally great thirst. ’ The symptoms that have been briefly described here are not shown, unfortunately, till many months, and sometimes several years, after the animal first contracted the infection. The incubation period in Johne’s disease — is to say, the interval that elapses between the time infection takes place and the time when symptoms are first shown—is seldom less than one and a half years and is often much longer than that. Consequently symptoms are not often seen in very young animals ; wasting and scouring frequently occur in yearlings, but this is almost invariably due to worms in the fourth stomach and intestine not to Johne’s disease. It is in animals from two years old upwards that scouring for no apparent reason should be considered suggestive of Johne’s disease. Treatment. There is no known cure for this disease. If treatment for diarrhoea is given during the stage when intermittent scouring is taking place, it may seem to have a good effect, but actually the diarrhoea would have ceased for a time in any case, and will later occur again in spite of any treatment. In countries where cows are of higher beef value than they are here a form of treatment is sometimes used that temporarily checks the scouring and enables a little condition to be put on the beast by special feeding before it is disposed of to the butcher, but, as stated above, there is no cure for Johne’s disease, and money spent on medicines is money thrown away. In addition to that it is merely continuing to endanger the rest of the herd to keep an infected animal alive. Prevention. A beast that is scouring with Johne’s disease passes large numbers of the causal organism in its droppings. Hence the pasture and drinking-water of the other cows are apt to be infected, and in this way the disease is spread amongst them. Unfortunately Johne’s bacillus can remain alive in soil , and water for a long time. . The exact time that it can survive is not known, and undoubtedly it varies according to the condition of warmth, moisture, and so on, that the bacillus is exposed to, but under conditions which favour it it can probably survive for between one and two years. • Swampy, low-lying areas are considered to especially favour the survival of the bacilli deposited on them by infected cattle, and to be important sources of fresh cases of the disease on affected farms. It is essential that such areas be either drained and heavily limed, or, if this is impracticable, fenced off completely. Apart altogether from Johne’s disease swampy areas tend to harbour infectious diseases of all sortsboth bacterial and parasiticand to deal with them in one or other of these ■ ways is always highly desirable.

There is a widespread belief in Britain and elsewhere that infection is more readily conveyed to cattle by drinking water that is contaminated with Johne’s bacilli than by grazing, and this is probably correct. Thus ponds, swampy pools, and other such surface waters which the cattle can stand in, as well as drink from are especially dangerous, and should be replaced wherever possible by concrete ■drinking-troughs, which are less liable to contamination and can be kept clean. The farmer seldom realizes the potentialities of. such contaminated water-supplies for conveying disease amongst his stock. It does not apply only to Johne’s disease, but to tuberculosis and infectious diseases generally. - Chain-harrowing paddocks that have harboured infected cows is a most useful aid in control, as the beasts’ droppings are then broken up and the sun is afforded a chance to dry them thoroughly and .sterilize them. Sunlight is One of the most powerful disinfectants, but it needs to be given a chance. . Heavy dressings with burnt lime are to be recommended. They are considered in France, where Johne’s disease is very common in -certain areas, to have given good results, and in the Channel Islands also the liming of infected pastures is claimed to have been most beneficial in reducing the incidence of fresh cases. How burnt lime produces the effect claimed for it is not known, but it may act through .some effect on the soil rendering conditions in it unfavourable for . the bacillus so that it dies out. It will be apparent that while these preventive measures have a highly important part to play, something more is required if much real headway is to be made. Especially is there need for some means of detecting animals in the early stages of the disease before symptoms .are shown. Unless this can be done we have very little hope of controlling the spread of the disease through the country, because of the fact that an infected animal may be capable of infecting others for some years before showing symptoms itself. During those intervening years it may carry the infection into, several herds. An instance of this sort was brought to the writer’s notice recently : A pedigree bull was sold by Ato B. Some four years later Johne’s disease began to appear in B’s herd. In the meantime the bull had been sold to C. About three years after his arrival, Johne’s disease appeared in C’s herd, and eventually the bull himself died of it. While there is no actual proof, inquiry provided strong circumstantial evidence that this seemingly healthy bull had carried the disease into both herds. Fortunately we now have a test which can be used to detect the presence of Johne’s disease in the early stages. The Johnin Test. There is no need here to discuss the development of this method •of testing for Johne’s disease. It will suffice to say that it is done by injecting small quantities of Johnin (similar to tuberculin) into the animal’s skin and noting the result. It is very similar to the modern method of testing for tuberculosis. The test is completed in seventytwo hours, and does not affect the cow in the slightest. This latter point is mentioned, as an owner sometimes expresses a fear lest the application of the test should put a cow off her milk.'

It is not as - reliable as the tuberculin test, and a great deal of skill and experience is required to apply and interpret the results of the test properly, but in the hands of an experienced veterinarian it can give the greatest assistance in detecting early cases of the disease. Johne’s Disease in New Zealand. . There can be no doubt that it was introduced here in infected, but apparently healthy, imported cattle. That is how it has reached all new countries, and considering what has been said above regarding its lengthy incubation period, coupled with the fact that until recent years there was no means of detecting such animals,’ it is not surprising that it should have been spread in that way. The first case that was ever shown to be Johne’s disease in New Zealand occurred in an imported cow in 1912. The animal was destroyed and instructions issued to field officers that specimens from any animal showing suspicious symptoms were to be sent to the Wallaceville Laboratory for examination. That instruction was issued because it was considered very probable that other imported animals besides the one detected and killed might well have brought the disease in during previous years. As a result of this a number of specimens were received from time to time and examined at Wallaceville, but none was confirmed. Nevertheless the disease must have been present, for in 1928 specimens were received from a suspicious cow near New Plymouth, and examination showed it to be a well-marked case of Johne’s disease. This occurrence reawakened interest in the disease. It was at once realized that this was unlikely to be the only case, and inquiries were immediately started. They revealed that a condition of this sort had occurred on several farms, but the' owners had not reported the affected animals to the Department, as they attributed the scourings to various noninfectious causes, such as a “ chill,” unsuitable food, retention of part of the afterbirth, ragwort poisoning, and so on, and, while the history of the cases aroused suspicion, there was no definite evidence that they were, in fact, cases of Johne’s disease. That being so a search had to be made for actual cases, and it was only after considerable time that these were eventually found. Johne’s disease was scheduled under the Stock Act in 1931 in order to give departmental officers the requisite authority to slaughter infected animals and pay compensation for them. Since the rediscovery of Johne’s disease in 1928 the Department of Agriculture has been active in its inquiries concerning the disease both in this country and abroad, and has taken advantage of all fresh information that has come to light, particularly as regards methods of testing cattle to detect the presence of the disease before symptoms are shown. At the present time in New Zealand we know of its presence on several farms in Taranaki and the Waikato, and it is likely that it is also present to a slight degree, and as yet undetected, in certain other dairying districts.

The action the Department is taking to check the spread of the disease as far as possible may be outlined briefly as follows :-

To protect the whole Dominion from Imported Infection. All imported cattle, from whatever country, must be accompanied by a veterinary certificate that they passed the Johnin test prior to shipment. •

To protect the South Island. view of the disease being as yet unknown in the South Island, all dairy cattle going from the North Island to the South Island, must pass .the Johnin test applied by a Government Veterinarian before they are allowed to leave the farm of origin.

■ To limit the Spread of Infection in the North Island. The best means of accomplishing this has been the subject of long and very careful consideration of all aspects of the question. It is a far more complicated matter than may be easily realized and the Department has no intention of binding itself to any hard-and-fast policy. It can be said at once that there is not now, nor will there be, any intention of slaughtering put infected herds. Such a measure, with full compensation to the owner, would be the best means of all if we knew definitely that the disease was limited to a few herds, but the time when any such action were possible has long since gone past. It is the intention to interfere as little as possible with the normal practice on affected farms. Apart from a desire to inflict as little hardship as possible, on the farmers concerned, the Department is actuated also by the fact that any drastic action would inevitably lead to concealment of the presence of the disease, and although slightly more drastic action than it is intended to take might be more effective on the farms where it could be put into operation, there would in reality be little to gain and a great deal to lose by being too severe. The action now being gradually brought into operation is that affected herds are to be tested with Johnin at half-yearly intervals and the reactors slaughtered. Compensation will be paid in accordance with the provisions of the Stock Act. The owner must notify the Department of any intending sales of stock, and these will, if considered necessary, be tested again prior to sale. Inspection of the farm itself will be made and advice given on general lines of prevention, including management of the herd and matters such as draining and liming of pastures. For the past two years this line of action has been in operation in two grade herds in Taranaki, and the progress made with this experimental trial warrants the hope that with the co-operation of the farming community the method will go a long way towards checking the spread of the disease. Farmers having suspicious cases are urged to report them without delay to the nearest office of the Department. It is obviously in their own interests as well as to the advantage of the dairy industry as a whole that they should do so. ■

. While the normal high quality of Zealand, meat has been well maintained, it seems to behove us to ask whether this suffices in view of developments in the world’s meat trade. It probably may be said with truth that quality is of more value in meat-marketing now than it ever was before. Some of our competitors in the world’s meat-markets assiduously have been increasing not only their output but the quality of that output. In regard to lamb, for instance, the point may have been reached where there is danger that our supremacy in regard to quality—a supremacy which is so valuable to usmay be challenged. The New Zealand sheep industry cannot face such a possibility with equanimity. Fortunately there is no clear reason why its previous valuable eminence in respect to quality of lamb and mutton cannot be maintained. — Annual Report, Director-General op Agriculture.