SWINE PLAGUE: SEPTICÆMIA HÆMORRHAGICA SUIS.
Definition. Synonym. Bacillus pestis suis, 0.8–1.5μ, nonmotile. Pathogenesis. Accessory causes, as in hog cholera: less vitality than in virus of hog cholera, bacillus in apparently healthy, deadly to birds and rodents. Lesions: like as in hæmorrhagic septicæmia, lungs suffer more than bowels, lymph glands swollen hæmorrhagic, liver and spleen may seem almost normal, bowels slightly congested, marked emaciation. Symptoms: Acute cases like hog cholera, shorter incubation—1 day, troubled breathing when driven, cough, congested petechiated skin, hyperthermia, costiveness followed by diarrhœa. Diagnosis: constancy and predominance of lung lesions and symptoms, nonmotile bacillus with polar staining, not gasogenic with glucose, very fatal to birds and rodents. Prevention: as in hog cholera. Immunization. Treatment: as in hog cholera dangerous. Serum-therapy.
Definition. A contagious bacteridian disease of swine, acute or subacute, characterized by a short incubation, hyperthermia, marked congestion of the mucosæ, petechiæ and circumscribed blood extravasations in the skin, subcutis, mucosæ, submucosæ, and tissues, swelling, congestion and petechiation of the lymph glands, and a marked tendency to inflammatory localization in the lungs.
Synonyms. Th. Smith identifies this affection with the “Schweineseuche” of Germany.
Bacteriology. The bacillus of Swine Plague (B. Pestis Suis) has already been described in the differential table of allied bacteria given under hog cholera. It is a short rod, with rounded ends, 0.8 to 1.5μ. × 0.6 to 0.8μ, staining readily in aqueous basic aniline colors and bleaching in Gram’s iodine solution. The staining is distinctly polar, the colored portions being more or less crescentic with the concave or straight border turned inward toward the central clear space. It is destitute of flagella and distinctly nonmotile unlike the very active bacillus of hog cholera. It further differs in its growth on potato which is slight, gray and waxy. On gelatine, too, it gives a feeble growth (or none) unlike the brownish colonies of the bacillus of hog cholera. It fails to liquefy gelatin. On agar the growth is more active, being grayish, translucent or brown. Those forming under the surface are like flat horizontal discs with a small microscopic elevation or knob in the center. It grows in milk producing little or no acid and no clot. It produces gas with none of the sugars—glucose, lactose, saccharose—in contrast with the gas production in glucose by the hog cholera bacillus. It shows much less vitality and hardihood than the hog cholera bacillus, growing but feebly between 65° and 70° F., and most actively at 97° to 100° F.; dying in 7 minutes at a temperature of 58° (moist); dying in 3 days when dried, in 4 to 6 days in the soil, in 10 to 15 days in water and instantly in 0.04 per cent solution of lime water.
Pathogenesis. It is pathogenic to swine, hens, pigeons, pheasants, sparrow, mice, guinea pigs, rabbits, cattle, deer, etc., showing not only a wider range than the hog cholera bacillus, but a more deadly action outside the genus suis. Inoculated birds die in 2 days, rabbits in 16 to 20 hours and guineapigs in 1 to 4 days.
Accessory Causes. These agree in the main with those of hog cholera already described so that it is needless to repeat them here. The principal distinctions depend on the lesser vitality of the swine plague bacillus outside of the animal body, and its wider range of pathogenesis outside the genus suis. Infecting materials that have been thoroughly dry for a week may be considered harmless, also that which has been more than two weeks in water, and that which has been more than a week in the soil. If, therefore, the buildings have been thoroughly disinfected, the simple disuse of yards and pastures for a fortnight, and of ponds of water for three weeks may suffice. In the case of hog cholera it may be necessary to abandon such places for 5 months or for the season.
Abandonment by swine is, however, insufficient: all susceptible animals, wild and tame, (see pathogenesis) must be excluded as any one of these may maintain the infection. The preservation of recovered swine on the premises, or the early return of the immune may become a means of preserving the bacillus for the next susceptible pigs that may be introduced. The bacillus of swine plague may be found on the air passages of swine and other animals that are not themselves, at the time, susceptible to the disease, and these animals accordingly become the occasions of what have been thought to be spontaneous outbreaks, and of invasions of fresh herds after the introduction of healthy pigs which have been thought to be beyond suspicion. The danger of the communication of the germ by wild birds and rodents would be enormous, but for the fact that it is so much more deadly to these animals than the microbe of hog cholera, that few survive to maintain the infection. Yet the rule ought to be, to exclude from the fields or premises occupied by new or susceptible pigs, all animals, that may by any possibility become the means of introducing the infection so recently prevalent. Though so easily destroyed when outside the living body, the microbe of swine plague can be carried by the apparently healthy living animal and we must rigidly exclude the possibility of this occurring.
Lesions. Acute and rapidly fatal cases of swine plague furnish lesions indicative of a hæmorrhagic septicæmia. The abundance of petechiæ on the skin, mucosæ, serosæ, and tissues generally, with circumscribed hæmorrhages, congestions, inflammations and exudations, agree in the main with what is observed in the acute examples of hog cholera. If the congestive or inflammatory lesions, concentrate in the lungs rather than the bowels it assists in the diagnosis of swine plague. The swelling and blood engorgement of the lymph glands are nearly alike in the more acute types of the two diseases. The spleen is less constantly enlarged than in hog cholera or swine erysipelas. In the subacute and chronic forms the lesions may be almost entirely confined to the enlarged and congested or hæmorrhagic lymph glands. Usually, however, the lungs are the seat of lobular or lobar pneumonia, affecting by preference the lower portions of the anterior and median lobes, and sometimes also the posterior lobe. The pleuræ are often involved, showing arborescent congestion, thickening, exudate, false membranes and hydrothorax. The exudate may at times fill up the interlobular connective tissue, even before the pulmonary tissue is materially involved suggesting a local infection starting at the pleural surface. The hepatised lobule has a general red color varying in depth at different points, and showing lighter yellowish or grayish spots representing the purulent air sacs and terminal bronchia, and necrotic foci. On section the bronchia often yield pus, while the pulmonary tissue oozes a bloody liquid rich in small lymphoid cells.
The liver and spleen may be all but normal, though in a number of cases they may be congested and softened. The stomach and bowels may be virtually sound, or they may show extensive congestion, petechiation and thickening of the mucosa at different points, with, in some cases ulcers, but these latter are mostly excavated and rarely assume the projecting, button-like, laminated form which is so characteristic of chronic hog cholera. Emaciation is a marked feature as in hog-cholera.
Symptoms. In the most acute type these may not differ from those of similar cases of hog-cholera. If there has been any opportunity of estimating the incubation it will be found to have been shorter, the skin and mucosæ have a darker red blush, showing first on the ears, breast, belly and inner sides of the thighs and forearms, the lymph glands are enlarged, and there is cough and dyspnœa if the patient is roused to exertion. The presence of petechiæ on the skin and of a very high temperature (107° to 109°) is to be specially noted. There are great prostration and dulness, complete anorexia, hiding under the litter, indisposition to rise, often weakness, staggering, paresis or even paraplegia, somnolence, and death in coma or convulsions.
In the subacute and protracted cases, there is the short incubation (1 day), followed by hyperthermia, drooping tail, hiding under the litter, flushed eyes, nose and mouth, impaired appetite, arched loins, hollow flanks, retracted abdomen, cough easily roused by driving, and signs of consolidated lungs in their lower parts (crepitation, suppressed murmur, abdominal or heart sounds etc.). After a day or two the skin becomes flushed and together with the visible mucosæ the seat of petechiæ. The superficial lymph glands are enlarged. The bowels are usually confined but as the disease advances diarrhœa may set in. There is rapid loss of condition, and the patient may die as the result of exhaustion, toxin poisoning, colliquative diarrhœa, or other condition.
Diagnosis during life is based largely on the shorter incubation, the greater reddening of the visible mucosæ, the comparative absence of abdominal tenderness, and offensive diarrhœa, and the constancy of the cough and other symptoms of broncho-pneumonia.
Post-mortem. It is marked by the constancy and predominance of the lung lesions, and the comparative absence of ulceration of the ileum, cæcum and colon, and especially of the projecting, laminated, button-like, necrotic sloughs.
The morphology of the bacillus, its habit of polar staining, its lack of automatic movements, its comparatively poor growth in alkaline bouillon, on potato, gelatine and agar, its inability to ferment glucose with the production of gas, its rapidly fatal action on hens and pigeons as well as on rabbits and guinea pigs serve to distinguish it from the microbe of hog cholera. (See table p. [38]).
Prevention. In this connection the reader is referred to the precautions, given under hog cholera, against conditions, hereditary, hygienic, climatic, dietetic, parasitic, etc., which lay the system more open to microbian invasion. In the matter of exclusion of the bacillus, the swine plague germ is less difficult to deal with, because it is so much more easily destroyed. Disinfect the buildings, and all contaminated objects as advised under hog cholera, clean yards, and shut up these and pastures or runs, and all infected water for one month. In case of public market yards and alleys, and railway loading banks, chutes, and cars, a thorough cleansing and disinfection may warrant that they may be put to use again immediately. No animals that occupied the yards before disinfection should be allowed to mingle with the new stock, as they at times carry the microbe, though themselves apparently healthy and immune. All regulations as to railway and boat transit, recommended under hog cholera, are equally applicable to swine plague. The possibility of protecting private herds, by keeping them in special pens, holding two or three each, is also the same for swine plague.
Immunization is somewhat more promising than in hog cholera. Metchinkoff and Th. Smith working independently found a fair measure of success in inoculating rabbits and guinea pigs with three to five small injections of sterilized bouillon cultures, agar cultures or blood, intravenously, intraabdominally or hypodermically. But as applied to swine it has not proved satisfactory, and the irregularity of the results and the tendency to induce unthriftiness have caused it to be abandoned.
Treatment. The therapeutics of swine plague like that of hog cholera is essentially unsatisfactory. Benefit might be derived in individual cases from a careful and judicious use of drugs to meet the special indications, but with the comparatively low value of the individual animal, the certainty of the multiplication of the deadly poison by the preservation of the diseased, and the extreme danger of its diffusion and extension, treatment is anything but commendable.
Serum-therapy has been advocated for years by De Schweinitz, and under the auspices of the Bureau of Animal Industry it has been given a wide trial, but it has not met with the full success that was at first claimed for it. The serum is prepared in a similar way to that of hog cholera and is similarly employed. It is open to the same class of objections, and though when skillfully employed it will reduce the mortality, it does not yet seem to have reached the point at which it can be recommended as a profitable investment. Like all temporizing measures it draws attention from the sounder and more economical measure of extinction and is indirectly a means of the perpetuation and even the diffusion of the infection. So long as extinction cannot be secured, this is a less valuable alternative for the adoption of owners of high priced hogs.