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.