Diseases of cattle, sheep, goats and swine

by G. Moussu; Jno. A. W. Dollar

SWINE FEVER—VERRUCOUS ENDOCARDITIS AND PNEUMONIA OF THE PIG.

Although it is not contemplated in this work to deal with those disorders which, on account of their highly contagious or infectious character, can only be dealt with by legislative action and by processes of “stamping-out,” it may be permissible to make certain exceptions. While we have made no reference to contagious pleuro-pneumonia of cattle, foot-and-mouth disease, rinderpest, anthrax and black-quarter we have devoted some space to Texas fever and tuberculosis, and give herewith a summary of the present state of knowledge regarding swine fever or hog cholera and a hæmorrhagic septicæmia of cattle known under various names in different countries and of very wide distribution.

SWINE FEVER.[^[9]]

[9]. Report of the Departmental Committee re Swine Fever. (Annual Report of Board of Agriculture, 1896.)

Swine fever may assume two distinct forms, viz., the acute and fatal and the non-acute or slowly progressive.

Symptoms. In the acute form all those symptoms which are indicative of a severe febrile affection are present. The animals are disinclined to feed; they present evidence of great prostration and lie about their dwellings in a listless manner sheltering themselves from cold; their skins are hot, their eyes partially closed, and they are obviously suffering from some severe constitutional disturbance. Within a very few hours after these premonitory symptoms have set in the pigs become rapidly worse; they may or may not have a deep-red blush on the skin, which is more particularly noticeable on those parts of the body where there is an absence of hair, such as the inside of the thighs, the point of the axilla, and over the abdomen. Choleraic evacuations, having a most offensive odour, succeeding upon constipation, follow later on, and the animals die perhaps as early as the third or fourth day after the symptoms have first been observed.

In some instances the disease proceeds with great rapidity through a herd, the symptoms being of a most aggravated and pronounced character, and the outbreak attended with great fatality.

Generally speaking, the above description depicts the symptoms of swine fever in the acute form, more especially when it breaks out in a herd of young pigs.

In the non-acute form the disease progresses slowly, the clinical evidence is extremely obscure, the reddening of the skin, formerly regarded as being invariably present in swine fever, is absent, and beyond the fact that the animal is unthrifty, develops slowly, and perhaps has a constantly relaxed condition of the bowels, it may be asserted that there are no symptoms which could be regarded as absolutely indicative of swine fever, and nothing short of a post-mortem examination will enable even an expert to satisfy himself that the animal was affected with the disease.

As a general rule swine fever assumes this non-acute and slowly progressive form in pigs which have arrived at an age when their powers of resistance to disease are materially increased, i.e., in animals of eight or more months old; on post-mortem examination they are found to have been extensively diseased, more particularly in the large intestine, a portion of the digestive apparatus which does not appear to perform any very important function in connection with the nutrition of the animal, and so long as the stomach and small intestines remain healthy, pigs with a considerable amount of disease in the large intestine may still keep up their condition for a considerable time.

Etiology. As regards the etiology of the form of swine fever prevalent in England no question now exists. It has been proved to demonstration by the bacteriological inquiry conducted by Professor McFadyean that it is due to a special pathogenic organism, a bacillus, which, after cultivation in artificial media, will produce in the healthy pig fed with the pure cultures the typical ulcerations which are found in the intestines of pigs affected with swine fever contracted in the ordinary way.

The observations made by the veterinary officers of the Board of Agriculture caused them to doubt whether there was any disease of the lungs of pigs which, in the absence of lesions in the intestinal tract, could be accepted as evidence of swine fever.

The bacillus which produced swine fever when introduced in the healthy pig did not induce any special disease of the lungs.

Pathology and morbid anatomy. Swine fever, like typhoid fever in man, is essentially a disease of the digestive system, its chief characteristic being certain morbid changes of a well-marked nature which are found upon the surface of the mucous membrane in some part of the alimentary canal.

The changes referred to consist of what have been commonly described as the formation of a series of ulcers, single or confluent, distributed upon some part of the intestinal tract, varying in size and shape, of a yellowish-grey to black colour, and assuming as a rule a circular form. In some instances the lesions consist of diphtheritic exudations with necrosis of the lining membrane of the bowels.

These ulcers or necrotic patches may be found upon the tongue, tonsils, epiglottis, stomach, and small intestines, but they are more constant in the large intestines, especially the cæcum and colon. The lesions may involve the whole thickness of the mucous membrane, but seldom penetrate the other coats of the intestine; in fact, perforation of the peritoneal covering of the bowel is very rare in even prolonged cases of swine fever.

In cases where swine fever assumes the more acute form and death supervenes rapidly, it is usual to find that the small intestines are largely involved.

In the non-acute or slowly progressing form the lesions are more abundant in the large intestines, and in some instances the walls of the intestines become so thick as a result of infiltration into their structure and the excessively thick deposits upon the lining membrane, that it becomes a matter of surprise that the passage of the ingesta has been possible and that the animal has lived so long.

Next to the intestinal lesions the congested condition of the lymphatic glands, especially those of the mesentery, may be considered as most prominent among the pathological changes which occur in swine fever. Occasionally centres of necrosis are observed in the liver, and some writers refer to changes in or upon the spleen and kidneys.

The only lesions which can be characterised as absolutely typical of swine fever are those present in the bowels, the absence of which will justify any observer in declining to accept the case as one of swine fever without some further evidence or inquiry. It must, however, be distinctly understood that in the case of very young pigs which have died shortly after infection, there is often an entire absence of the lesions described, the only changes present being inflammation of the stomach or some part of the intestines.

Further, there are instances where older pigs have been slaughtered in the early stage of the disease in which no definite lesions have been found, and in such cases inquiry into the condition of the rest of the herd becomes necessary.

One most important feature in connection with the morbid anatomy of swine fever is the disposition which many animals have to recover from the disease; evidence of the reparatory process having often been detected in the intestines after they had been carefully washed.

Dr. Klein also maintained that many pigs took the disease in the mild form, and recovered without presenting any of the marked symptoms of swine fever.

It was found that, whether infected in the ordinary way or by direct inoculation, in some pigs killed only a few days after being infected the ulcers were occasionally seen gradually detaching from the surface of the intestines, and cicatrisation had already commenced.

VERRUCOUS ENDOCARDITIS OF THE PIG.

In the report of the Board of Agriculture for 1894 reference was made to the numerous instances in which the heart of the pig had been found affected with verrucous endocarditis.

This form of disease of the heart was known to veterinarians in Great Britain as far back as the year 1847. For reasons given in that report it became obvious that this diseased condition of the valves of the heart was not produced by swine fever. The question arose whether in addition to swine fever another disease existed, known on the Continent under the name of swine erysipelas. The importance of this question will be appreciated when it is explained that on the Continent swine erysipelas is classed among the contagious diseases of the pig.

The clinical evidence of the disease called swine erysipelas on the Continent appears to be more or less discoloration of the skin, similar to that which is frequently observed in swine fever, together with the occasional presence within the warty growths upon the valves of the heart of a bacillus which is regarded by Continental authorities as the cause of the disease.

Early in the inquiry it was ascertained that a bacillus identical with that found in swine erysipelas was also present in the diseased portion of the valves of the heart of the pigs in this country.

But the inquiries made did not corroborate or favour the suggestion that the disease which produced these morbid growths was in any way infectious or contagious. Such inquiries as could be made led to the opposite conclusion, since in every instance where the cases could be followed up it was ascertained that the deaths had been quite sudden, were limited to a single animal, and that those in contact remained in perfect health.

At this stage the all-important point to determine was whether the disease which existed in this country, “verrucous endocarditis,” was communicable from pig to pig, and with this object numerous experiments have been conducted to discover whether the bacilli found within the hearts of diseased pigs were pathogenic to healthy swine.

A large number of healthy pigs have been fed or inoculated with the blood, the diseased portions taken from the valves of the heart, and with artificial cultures of the bacilli obtained from the heart, but in no instance has the attempt to produce this disease been successful.

PNEUMONIA OF THE PIG.

The occasional association of pneumonia with or without pleurisy in cases of swine fever has led many veterinarians in England to regard lung complications as one of the lesions produced by that disease.

In the Board of Agriculture’s report for the year 1894 a description was given of the various diseases in the lungs of swine which had come under notice, and it was therein stated that the Board had been unable to discover any special lesion of the lung which would warrant them in stating that it was indicative of swine fever or due to contagion.

It is an indisputable fact that pigs are extremely liable to pneumonia and pleurisy. But as the clinical appearances present in the lungs examined in no wise differed from those which take place in the lungs of other animals which have been exposed to cold or septicæmia and other causes, the Board’s officers have never accepted these lesions as being specific.

It is well known that both in Germany and the United States outbreaks of pneumonia of a contagious nature attributed to the presence of a bacillus pathogenic to the pigs of those countries are reported to occur. Indeed, contagious pneumonia of swine under the names of schweineseuche in Germany and swine plague in America are regarded as one and the same disease.

In view of the fact that in a large number of cases pneumonia, more or less extensive, sometimes associated with pleurisy, was found among the specimens forwarded to London, it was considered desirable that the departmental committee should institute a series of experiments to decide whether we had in this country a form of pneumonia in the pig which was communicable from one pig to another.

Accordingly a series of bacteriological experiments were conducted by Professor McFadyean with a view to isolate, if possible, a microorganism which would be capable of inducing pneumonia in healthy pigs. A number of diseased lungs, some of which were taken from pigs affected with swine fever, were examined microscopically by him, and, as was to be expected, several organisms were isolated, but they proved to be morphologically and culturally different from the bacillus of swine fever. Inoculations were carried out with these organisms not only subcutaneously but directly into the lung through the walls of the chest, and feeding experiments were also conducted. The results of these experiments were entirely negative; a certain amount of local injury was caused to the lungs at the seat where they had been punctured, but in no case was either pneumonia or swine fever induced.

The experiments have therefore demonstrated that the pneumonia found in the lungs of pigs affected with swine fever is not due to the swine fever bacillus.

The departmental committee arrived at the conclusion that the pneumonia which is occasionally encountered as an independent disease of the pig or in association with swine fever is not ascribable to contagion, but to the presence of organisms which are generally saprophytic in their mode of life, and which only in particular circumstances (such as lowered vitality and diminished resistance on the part of the pig) are able to multiply in the air passages and lung tissue and thus induce pneumonia; and it appeared to the departmental committee that in this country pneumonia of the pig is sporadic and not contagious or epizootic.

CONCLUSIONS.

There is now no reason whatever to believe that there exists at the present time in Great Britain any disease of a contagious nature affecting pigs other than swine fever. The disease of the heart, “verrucous endocarditis,” and the pneumonia which are so frequently met with in pigs cannot be regarded as lesions indicative of an attack of swine fever.

As regards verrucous endocarditis and pneumonia, it may safely be said that they do not exist in England in a contagious form.

Considering all the evidence, it may reasonably be concluded that the departmental committee were correct in their views when they stated that “the evidence obtained during the whole inquiry justifies the conclusion at which they have arrived, viz., that there is no epizootic of swine except swine fever in any part of the United Kingdom which requires to be dealt with under the provisions of the Act of 1894.”

Finally, it may be said that the great factors in perpetuating swine fever will always be pigs which are affected with that disease in the less fatal and unrecognisable form. These animals are constantly distributing the germs of swine fever through their highly infective evacuations wherever they may be taken during the whole period of their illness, and the final extinction of the malady must depend upon the possibility of enforcing measures which will have the effect of preventing the movement of pigs affected with swine fever in this particular form.