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PRELIMINARY INVESTIGATIONS CONCERNING INFECTIOUS PNEU.
MONIA IN SWINE* (SWINE-PLAGUE,
In prosecuting investigations in the West in order to determine whether the disease which has been described in these reports as hog-cholera existed there also, the lesions characteristic of this disease and the specific bacterium were found in Illinois and Nebraska. At the same time another microbe was found, resembling in its microscopical characters the microbe of rabbit septicæmia very closely, and associated with disease of the lungs—a chronic pneumonia-in the few cases which were examined. Although the investigations concerning the nature of this microbe, its distribution, and the losses it produces, are scarcely begun, we venture the conclusion that it produces an infectious pneumonia in pigs, and that its effect may perhaps be spent upon organs other than the lungs. This conclusion is based upon the facts recorded in the following pages.
Among the post mortem examinations made in the State of Illinois in July, 1886, the following are worthy of attention:
In Marion County, a few miles from Patoka, a herd was found, July 7, of which about ten had died and an equal number were still alive. Through the kindness of the owner several pigs, which were evidently diseased, were killed by a blow on the head. In No. 1 the superficial inguinals were greatly enlarged; ecchymoses were found in the subcutaneous fatty tissue in large numbers on the omentum and the epicardium. The lymphatic glands were as a rule enlarged and purplish, the spleen augmented in size, the major portion of the lungs hepatized, and the remainder interspersed with hemorrhagic foci. The mucous membrane of the stomach and the large intestine was ecchymosed, that of the latter presenting here and there deep ulcers, especially on the ileo-cæcal valve. Cover-glass preparations from the spleen of this case contained no bacteria of any kind. Å tube of gelatine into which a bit of spleen had been dropped remained sterile. No. 2, from the same herd, also killed at the time, was affected with a suppurative pyelitis of the right kidney, causing inflammatory adhesions of the large intestine. The mucous membrane of the latter was dotted with innumerable petechiæ and a few ulcers. Cover-glass preparations from the spleen of this animal were equally negative. A tube of gelatine into which a bit of spleen tissue was dropped began to liquefy very slowly. It contained a bacillus and a large oval coccus.
No. 3, from the same herd, killed, had its lymphatic glands generally enlarged and purplish, the spleen dotted with numerous blood-red elevated points, lungs with large carnified areas. The mucous membrane of the large intestine was merely congested. No bacteria seen in cover-glass preparations of the spleen, and a gelatine culture made as before remained sterile.
Several miles east of Champaign, Ill., the disease was appearing in a herd, the owner of which very kindly permitted us to make what examinations we thought advisable. On July 8 two autopsies were made. In No. 4, dead since last night, the lymphatic glands generally were enlarged and purplish. The subcutaneous fatty tissue stained yellow. The peritoneal and pericardial cavity contained a considerable amount of yellow serum. The only other marked lesion observed was an enormous enlargement of the spleen, which was very dark and pulpy. The mucous membrane of the alimentary canal apparently intact. These lesions did not point to hog-cholera. Cover-glass preparations of the spleen were negative. A piece dropped into a tube of gelatine slowly liquefied the latter. A bacillus was found in it, not pathogenic.
A pig (No. 5) which was observed to be very weak, although able to move about when disturbed, was killed for further information. In the subcutaneous tissue over the abdomen were numerous ecchymoses. The inguinal glands were greatly enlarged, cortex purplish, some lobules deeply congested throughout. The abdominal cavity contained a small quantity of colorless serum; the spleen considerably tumefied and covered with blood-red raised points. The lymphatic glands about the
*We shall call this disease swine-plague, in distinction from hog-cholera, just described. See introductory remarks to Diseases of Swine, p. 603.
stomach, as well as the bronchials, were deeply congested, the cortex infiltrated with blood. The epicardium was dotted over its entire surface with minute extravasations. The mucous membrane in the fundus of the stomach and of the entire length of the large intestine covered with closely-set extravasations. Cover-glass preparations, as well as cultures of the spleen, were entirely negative.
Reports of swine-plague from Geneseo, Henry County, made it advisable to make a few post mortem examinations in this section of the State, in order to make sure of the nature of the disease. The losses were very heavy, involving in many places the greater part of the affected herd. July 11 several autopsies were made in a herd about 3 miles from Geneseo. In this herd the disease had been observed about nine days before. At the time three or four large animals had died during the night and a number of others were ill.
No. 6.-Adult black male, in good condition, no signs of decomposition. In the peritoneal cavity there were ecchymoses beneath the peritoneum of the dorsal wall, near the caudal end of the kidneys, at least an inch in diameter. The spleen was enlarged and congested. Whitish patches showing through the serosa of the large intestine were afterwards found to correspond with ulcerations of the mucous membrane. The lymphatic glands in general with congested cortex. The left lung completely solidified, blackish, and everywhere adherent to chest wall. On forcing the ribs apart the lung tissue broke as a watermelon would; from the broken surface a blackish frothy liquid exuded. A portion of the right lung was in the same condition. A fibrinous deposit on the epicardium indicative of pericarditis. In the alimentary tract the mucous membrane of the fundus of the stomach is darkened with extravasations on the ridges of the folds. In the large intestine the mucous membrane is completely covered with punctiform extravasations, in part converted into pigment. In the cæcum and colon are isolated disk-shaped ulcers about one-half înch in diameter, slightly elevated. The center is dark, surrounded by a broad yellowish margin, giving the whole a button-like appearance. On section a whitish tough tissue is found to make up the ulcer and extend to the peritoneum, where it appears as a whitish patch when viewed from the serous surface. Cover-glass preparations of the spleen negative. Two portions dropped into a tube of gelatine and agar-agar respectively gave rise to cultures which will be described in detail farther on.
No. 7.-A small shoat, having shown signs of disease for a few days, was killed by a blow on the head. The superficial inguinal glands were enlarged and reddened. Both kidneys dotted on the surface with minute petechiæ. On section a few are found in medullary portion. The spleen is dotted with a few blood-red elevated points. Cover-glass preparations of the spleen negative. Cultures remain sterile.
No. 8.-Large black sow; died last night. Adipose abundant. In this animal the spleen was enlarged, the medullary portion of kidneys deeply reddened, lungs normal. The mucosa of the large intestine was entirely covered with minute elongated spots of pigment, representing former extravasations. Cover-glass preparations of spleen also negative. A gelatine tube containing a portion of spleen contained a micrococcus. Bits of the spleen introduced beneath the skin of the dorsum of two mice made them ill for a few days. Both finally recovered.
Besides the cultures mentioned in the autopsy notes at least ten others were made at the time by piercing the spleens with a platinum wire and then piercing with it tubes of gelatine or drawing it over the surface of tubes of agar-agar. None of these showed any signs of growth, thus confirming the supposition, derived from the examination of cover-glass preparations, that the specific microbes are either entirely absent from the spleen or else are present in very small numbers.
The lesions found in all but three cases, in which the ulceration of the large intestine was present, were not sufficiently uniform to warrant the diagnosis of hog-cholera. Viewed by the light of later observations, it seems highly probable that the remainder of the animals were affected with a different malady, due to the presence of the microbe to be described later on. The ecchymosis of the large intestine and the congestion and tumefaction of the lymphatics generally differed from the lesions which we have found in hog-cholera. The absence of bacteria from the tissues is also suspicious. There was moreover a partial cirrhosis of the liver in most of the animals examined which we have never encountered in hog-cholera. We must remember, however, that of these eight cases five were killed, perhaps in the early stages of the disease, before the lesions were well marked. Leaving these observations for future interpretation, when more cases have been examined we will proceed to a description of the bacteriological investigations.
In a few among a large number of tubes bacteria were present. Nearly all were found harmless when inoculated into animals very susceptible to hog-cholera. In two tubes inoculated with bits of spleen from No. 6 two microbes were found which deserve attention.
One grew in both tubes, which was more carefully examined, because it resembled the bacterium of hog-cholera very closely. In liquid media it is actively motile and simulates the form of a bacislus. When stained, however, each individual is resolved into a pair of ovals or very short rods with rounded extremities. A deeply stained narrow border surrounds a comparatively pale body. There seems to be slightly more stained material at the two extremities than in the bacterium already fully described in the last report. It seems a trifle longer than the latter form, but on attempting to confirm this impression by measurement the dimensions were found practically the same. Sown on gelatine plates the colonies appear within twenty-four hours and grow quite rapidly. The deep colonies are spherical, with smooth outline and homogeneous disc. The surface colonies appear as irregular patches, spreading very quickly, and, as a rule, growing far more vigorously than the deep colonies. In tubes containing nutrient gelatine the isolated colonies in the depth of the needle track may grow to the size of pins' heads. On the surface a flat, thín, pearly layer rapidly extends from the point of inoculation, and in from one to two weeks may have covered the entire surface. The pargins are irregularly scalloped and lobed, the entire layer often simulating the frost flowers on windows or lace work (Plate V, Fig. 2). On potato, a thick straw-colored shining layer of nearly smooth surface forms, which grows very vigorously and gradually covers the entire cut surface of the potato with a layer 2mm thick. This growth is brighter in color and more abundant than appears in the potato culture of the bacterium of hogcholera. Cultivated in liquids, such as beef infusion with 1 per cent. peptone, the medium becomes very turbid within twenty-four hours. A thin pellicle appears, which soon becomes a thick membrane. A cream-colored deposit forms and accumulates to a considerable extent, while the liquid remains turbid. It will be remembered that the bacterium of hog-cholera grows very feebly in comparison.
No resistant spore state was found, for tubes exposed to 58° C. for fifteen minutes remained sterile; those exposed ten minutes became turbid. The pale, unstained central portion of the bacterium simulates very strikingly the appearance of an endogenous spore, yet they all succumb to the temperature of 58° C., as described. A peculiar property not common to the hog-cholera bacteria described is the coaguIation of the casein of milk. If a tube of this liquid, sterilized by discontinuous boiling, be inoculated, it will be solidified within twenty-four hours. The coagulum, contracting later on, leaves a shallow stratum of watery liquid near the surface. The reaction is acid._Grown on gelatine a rather penetrating odor of decomposing flesh is given off. The bacterium of hog-cholera develops no odor whatever in cultures. This microbe, therefore, resembled the bacterium of hog-colera very closely in its microscopic characters, but differed from it in some of its physiological properties. This illustrates how important cultivation experiments are in the determination of specific differences. That it was not the bacterium of hog-cholera was shown by an utter want of pathogenic properties when inoculated into mice and rabbits. Pigs were inoculated and fed; cultures were introduced per rectum without any effect whatever.
In one of the tubes the motile bacterium just described was mixed with another microbe, which proved to be a very virulent germ. It was obtained pure as follows: A rabbit inoculated with the mixture from a liquid culture made from the original gelatine tube died in seven days, after showing signs of lameness for several days. The inoculated thigh was enlarged, the skin bluish. The subcutaneous connective tissue was of a leathery consistency. The surface of the muscular tissue on the inner aspect of the thigh was of a uniform yellowish gray; this change extended into the muscular tissue to the depth of 3mm (one-eighth inch); the striated appearance was lost. This change also involved the deeper intermuscular septa of the thigh. On the abdomen the subcutis was infiltrated with a blood-stained serum. The local effect had thus been unusually severe. Cultures from the spleen, liver, and blood in gelatine tubes contained only the second microbe. The one above described had no power of invading the tissues of the rabit. That the microbe obtained from the tissue of this rabbit was pathogenic the following experiments clearly demonstrate:
With pure liquid cultures of this microbe three mice were inoculated. Two of these died within one and two days of inoculation. In the spleen of both peculiar torula-like forms were found, presumably the cocci in process of division, which was retarded by unfavorable conditions. Its effect upon a rabbit, however, was more pronounced. This rabbit died three days after a hypodermic injection of fcc of a liquid culture. Beneath the skin of the inoculated thigh there was a translucent gelatinous exudate about one-half inch thick. The muscles of the thigh and of the contiguous wall of the abdomen were dotted with closely set punctiform and larger extravasations. In the abdomen they were very numerous on the large intestine along a zone nearest the abdominal wall. They were also found over the kidney and on the psoas muscle. Spleen not enlarged, dark; liver rather pale; acini well marked; the entire right lung and base of the left deeply congested; very few bacteria in the internal organs. Two liquid cultures of blood and one from liver contained the injected microbes. Gelatine cultures of blood, spleen, and liver developed into numerous colonies of the same microbe in the needle track.
Two pigs (Nos. 287 and 289) were inoculated September 11 from a culture of the rabbit. Each received beneath the skin of the thigh 24cc of the culture liquid. No. 287 became dull and lost its appetite several days later; eyes discharging. September 28 the animal became delirious and ran blindly about the pen; dead next morning; The only observable lesions were local swellings two inches across and one-fourth to three-fourths inch thick, with centers which were beginning to soften. Blood very dark, not coagulated; a few petechiæ on epicardium. The liver was very pale, sclerosed; the medulla of kidney deeply reddened. No. 289 died September 21, after exhibiting the same symptoms; local swellings as above, without indications of softening; the connective tissue and fat of the whole body of a deep yellow color; liver very firm, bloodless, and of a peculiar yellowish red color throughout; medulla of kidneys deeply reddened; two large cysts in the right one. In neither case was the alimentary tract diseased. In both there was cirrhosis of the liver, producing in the second animal a general jaundice. From neither were cultures of the inoculated microbe successful, though blood from the heart, the spleen, and the liver were used. The tubes remained sterile.
Nos. 288 and 290, which had been retained in the same pen, did not contract the disease from the others, as would ordinarily happen in hog-cholera. No. 288 was fed with hog-cholera viscera October 12, and died from the effects December 4; cæcum and colon ulcerated. No. 290, fed at the same time, died October 28, the only visible cause of death being retention of urine.
This microbe was, therefore, fatal to mice, rabbits and pigs, producing in the pig an acute inflammation of the liver, leading to a marked cirrhosis and general jaundice.
The same disease found near Sodorus, Ill.—The same microbe was obtained from an outbreak in Sodorus, Illinois, several months later. On page 630 a description is given of two post mortems, in one of which (No. 1) the lesions were ulceration of the large intestine and a grayish hepatization of the lungs. From this animal the bacterium of hog-cholera had been obtained from the spleen. In the other animal (No. 2) the lung lesions only were present. Portions of the solidified lung tissue from No. 2, hardened in strong alcohol, were submitted to a microscopic examination. The tissue was infiltrated with paraffine, the sections treated with turpentine to remove the imbedding substance, and then stained in various ways. The smaller bronchi and air-cells were completely filled with an exudate, consisting of white blood corpuscles chiefly, and some larger pale cells, probably derived from the epithelium. This infiltration was exceedingly dense in many places; in others less so. The septa or alveolar walls were not perceptibly affected, but the capillaries were distended with blood corpuscles, and formed an unstained mesh-work around the deeply stained alveolar contents. The interlobular connective tissue was also infiltrated, and the lymphatic spaces
distended and filled with a fibrillar network of coagulated lymph. When the alveolar contents were carefully examined with a one-eighteenth homogeneous objective, after staining the section in Löffler's alkaline methylene blue for several hours and decolorizing in one-half per cent. acetic acid, groups of very minute oval bacteria were recognizable, in size and outline like those obtained in cultures from the pleura. These groups were very large and extended through the depth of the section, à fact easily recognized by focusing up and down. They were found in all parts of the section, the bacteria themselves and the groups they formed being readily recognizable. No other bacteria could be detected, though the sections were searched over many times. Staining in aniline water methyl violet overnight did not bring these groups out so clearly as the stain above given. These groups, moreover, were present in those air-cells chiefly in which the exudate was but moderately dense.
The lesions of the lungs found in both pigs at Sodorus, Ill., were different from those occasionally found in post mortem examinations of hog-cholera at the Washington Experimental Station. In the latter the acute cases, characterized by hemorrhagic lesions in various organs, usually presented lungs which were dotted with dark red patches visible on the pleural surfaces and in the parenchyma. These were evidently extravasations into the alveoli, and etiologically the same as the extravasations found elsewhere. In the majority of cases lung lesions were entirely absent. When present they were usually associated with an abundance of lung worms in the bronchi. In many cases the small anterior lobes resting laterally upon the pericardium were collapsed (atelectasis), of the color of red flesh. This condition seems to stand in no direct relation to the disease itself.
The broncho-pneumonia found in the pigs above referred to extended over at least one-half of the lungs, involving the caudal portion of the base, resting on the diaphragm. The pleura was but slightly affected; a few adhesions and a more than normal quantity of serum on its surface constituted the visible changes. The lung tissue itself was airless, solid, of a grayish red, somewhat mottled. From the pleural surface of No. 2 two tubes of gelatine were inoculated by dipping into them a loop of platinum wire filled with serous exudate. The heat of the weather liquefied both tubes soon after, and within a few days the gelatine in one of them was densely crowded with small whitish points; in the other tube the colonies were fewer in number and consequently much larger. Both were,