Definition. Comparative immunity of sucking pigs. Disease unknown in
America. Causes: Bacillus erysipelatos suis, mature age, infection
through yards, buildings, troughs, dust, mice, rabbits, pigeons, men,
dogs, vermin, birds, butcher’s and kitchen scraps, swill, hot weather,
damp seasons, close pens, movement of swine, stockyards, fairs, public
conveyances, public highways. Symptoms: incubation three days, chill,
violet mucosæ, hyperthermia, recumbency under litter, muscular
weakness especially behind, inappetence, thirst, costiveness, later
diarrhœa, tenderness to touch, lymph glands swollen, red, blue, violet
or black discoloration of skin, cutaneous swelling and pitting.
Course: death in 12 hours to 6 days, or convalescence prompt.
Mortality 20 to 80 per cent. Lesions: congestion of capillary vessel,
blood extravasations, petechiæ, affecting cutis and subcutaneous fat,
lymph glands congested, discolored; lungs engorged; spleen enlarged,
liver and kidneys congested, petechiæ general, blood little altered.
Bacillus 1.5 μ, anærobic, easily destroyed in pens, in pork.
Pathogenesis: swine, rabbits, mice, rats, pigeons and sparrows suffer.
Rabbit germ less fatal to pigs. Immunization, advantages and
drawbacks. Technique.
_Definition._ A microbian disease of swine manifested by high fever,
great prostration and muscular weakness, a violet tint of the visible
mucosæ, red or violet discoloration of the skin in spots and patches or
universally, enlarged lymph glands, encreased size of the spleen, and
general congestion of the capillary plexus.
Contrary to the habit of hog cholera and swine plague, rouget attacks
mature swine mainly, the sucking pig showing a remarkable power of
resistance. It does not appear whether this is due to the animal (milk)
diet or to the absence of infection from feeding in the trough used by
the adult animals. Up to the present this disease has not been
recognized in America.
_Causes._ The one essential cause of rouget is the presence of the
bacillus. The other conditions are either such as predispose the animal
to receive it, for example, mature age: or they are such as favor
diffusion of the poison, such as the introduction of an infected animal,
the feeding of the healthy from the same manger with the infected, the
introduction into the manger of the feet or snout which have become
soiled with the infected manure or urine, the distribution of the
infection in dust, the introduction of the bacillus in the bodies of
mice, rabbits, or pigeons, or on the feet of those animals, of men,
dogs, birds, and vermin. We may add the distribution of infection in
dried butcher’s scraps used in pig feeding, and in uncooked scraps from
the kitchen or in hotel swill.
It has been noted that the highest mortality prevails in hot summer
weather, in damp seasons, and in narrow, confined, badly ventilated
pens. Under such circumstances the introduction of a diseased pig will
lead to the infection of most of the others in a few hours. Infection is
quite as prompt through public pens in stock yards and fairs, and in
public conveyances (cars, stock wagons, steamboats, ferry boats, etc.)
and public highways.
_Symptoms._ After a period of incubation of three days or more the
subject is seized with shivering, the limbs are hot and cold
alternately, respiration and heart beats are accelerated, the mucous
membranes assume a dark violet tint and the rectal temperature rises to
104° to 108° F. From the first the pig tends to bury itself under the
litter, and refuses to move unless absolutely forced to do so, and then
only with painful grunts, swaying and staggering limbs (especially the
hind ones), and straight drooping tail. There is inappetence, but thirst
remains, and the bowels are at first costive, the manure being covered
with a film of mucous or even streaks of blood; later they become
relaxed and diarrhœa becomes often a prominent symptom. The pig seems to
suffer and often squeals when handled, and he may give a weak, dry
cough. The external inguinal glands may often be felt perceptibly
enlarged. The red discoloration of the skin appears early and extends
and deepens to the end in fatal cases. It may be of a bright red, or of
a bluish red, violet or black. The first indications appear as spots, by
preference around the roots of the ears, on the breast and abdomen,
inside the arms and thighs, and in the perineum. These isolated spots
run together into great patches, which extend over the whole ventral
aspect of the body, and may cover the entire dorsal aspect as well. In
some instances the skin is swollen and retains an impression made by the
finger.
_Course._ The disease may reach a fatal termination in twelve hours:
more commonly it endures for forty-eight hours, and at times it will
last for four, five or six days. In the most rapidly fatal cases, the
violet discoloration of the skin may be absent or only a little marked,
while in the protracted cases it acquires its greatest extensions and
its darkest shades. In the protracted cases too the prostration becomes
extreme, the animal may find it impossible to raise himself on his hind
limbs, the diarrhœa becomes profuse, liquid and fœtid, the respiration
labored, cyanosis sets in and the temperature is reduced below the
normal standard.
In case of recovery, convalescence is usually prompt and complete,
differing in this from cases of swine plague and hog cholera. The more
favorable issue in rouget probably depends on the comparative integrity
of the intestinal mucosa and mesenteric glands, which are subject to
slow healing lesions in swine plague and hog cholera. Slow convalescence
is however not uncommon, yet in such cases, the concurrent, speedy and
complete recoveries in other animals in the same herd serve to identify
the disease as rouget.
_Mortality._ The mortality among grown hogs averages eighty per cent.
_Morbid Anatomy._ The most prominent lesion is the general congestion of
the capillary blood vessels, and the numerous minute extravasations or
petechiæ. The skin shows in the red patches a general dilatation of the
capillaries which have become at the same time elongated and tortuous,
with minute, often microscopic, ruptures and extravasations at frequent
intervals. This usually extends to the whole thickness of the cutis, and
to a considerable depth in the subcutaneous fat. Where swelling occurred
or pitting on pressure, a serous infiltration of the tissues is found.
The lymph glands are uniformly enlarged and discolored, of a dark red,
almost black, color, the congestion and extravasation being extreme in
the cortical substance, while the medullary is paler, soft and cellular.
The lungs are usually gorged with black blood suggesting death by
asphyxia. In tardy cases there may, though rarely, be centres of
broncho-pneumonia. The spleen is enlarged, with dark color and uneven
surface from rounded swellings, and is filled by a soft black, bloody
pulp. The liver is congested, the kidneys congested, enlarged and
petechiated, and the gastric and intestinal mucosa congested and
thickened, with desquamating epithelium, and swollen solitary and
agminated glands, the degree of alteration usually bearing a ratio to
the duration of the disease. The serosæ are usually extensively
petechiated and serous effusions occur into the serous cavities. The
muscular substance of the heart and the endocardium are also the seats
of petechial extravasations. Unless in some protracted cases the blood
appears to be unaltered as regards its power of taking up oxygen, or
coagulating.
_Bacillus of Rouget._ The germ of this disease is found in small numbers
only, in the blood and vascular tissues, but very abundantly in the
lymph glands, the spleen, the kidneys, and the red marrow of the bone.
It is also present in enormous quantities in the urine and the bowel
dejections, the former (urine) offering a ready means of diagnosing the
disease microscopically.
The bacillus is 1µ to 1.5µ long by 0.1µ to 0.15µ broad, is nonmotile,
and stains readily even in Gram’s solution. They occur either solitary
or in pairs tending to unite at an angle. In old artificial cultures
chains of considerable length may be formed. In the blood the bacillus
is usually found in the leucocytes, as many as 20 or more being often
present in a single cell. In the lymph networks of organs they also
invade the leucocytes but are found in free masses as well. The bacillus
is anærobic, but facultative ærobic, its preference being manifestly for
the absence of oxygen. It is non-liquefying. In gelatine cultures no
development takes place on the surface, but along the line of puncture a
delicate cloud-like branching growth takes place which extends
horizontally in parallel masses from the central puncture. This
resembles but is not quite so delicate as that formed by the bacillus of
mouse septicæmia with which it is supposed to be identical. It grows
scantily on the surface of nutrient agar or blood serum, but not at all
on bouillon, in the bottom of which, however, it forms a slight grayish
white deposit. It does not grow on potato. The bacillus sometimes shows
refrangent granules which have been supposed to be spores, but this idea
appears to be negatived by the ease with which its vitality is destroyed
by heat and disinfectants. The thermal death point is 68° C. (137° F.)
maintained for 10 minutes (Sternberg). Boulton found that it was killed
in 2 hours by mercuric chloride (1:10000), by carbolic acid solution
(1:100), and by sulphate of copper solution (1:100).
It is killed by desiccation, by quick lime and by chloride of lime. At a
temperature of 18° to 27° F. it perished in 13 days. In salted pork it
lost vitality in one month.
_Pathogenesis._ The bacillus is pathogenic to swine, rabbits, white
mice, house mice, white rats, pigeons and sparrows. Field mice, guinea
pigs and chickens are immune.
Mice and pigeons take the disease most certainly, and die in three days
to five, the whole body swarming with bacilli. Rabbits take the disease
less certainly or rapidly, inoculation in the ear causing first an
erysipelatoid inflammation and recovery with immunity often takes place.
_Immunization._ When inoculated continuously from rabbit to rabbit it
encreases its potency for that animal, which it comes to kill in 24 to
48 hours, but in the same ratio it loses its virulence for swine upon
which it can then be inoculated without danger to their life.
It was on this basis that Pasteur and Thuillier established in 1883,
their preventive inoculation for rouget. The method has been most
extensively employed in Europe, and where intelligently employed has
prevented this disease. From the laboratory at Buda-Pest alone, there
was sent out in one year material for 249,816 swine.
The objections to the method are: the danger of mistaking hog cholera
and swine plague respectively for rouget, as the rouget mitigated germ
would be in no sense protective against these; and the danger of
spreading the germs of rouget in fresh localities and thus introducing a
new plague instead of controlling and preventing an old one. In the
Baden experiments 5.4 per cent. of inoculated pigs died, and of 118
unprotected pigs exposed to them 62 per cent. contracted the disease and
one died. In France and Hungary, on the other hand, 1 to 1.45 per cent.
died of the operation, instead of 20 per cent. when the disease was
contracted in the ordinary way.
It is held that the danger lies largely in the inoculation of very young
pigs, and Nocard advises to operate only on those of four months and
upward.
The danger of spreading the germ by inoculation may be the more easily
guarded against, considering that it is very destructible by
disinfectant agents (heat, dryness, cold, chloride of lime, quick lime),
and that it does not readily survive in a locality, where it cannot find
a constant succession of victims. Yet the practice ought to be confined
to herds exposed to infection, and under special precautions, as regards
the exposure of other herds.
The _technique_ of the Pasteurian inoculation is to inject, subcutem, on
the inside of the thigh, 0.1cc. of the weaker preparation (premier
vaccin), and twelve days after a similar dose of the stronger one
(deuxieme vaccin).
This produces a mild attack of the disease from which the great majority
recover, and though they still react somewhat to a second and third
inoculation yet the disease so produced is rarely fatal.