This is a fatal affection of cattle met with in the counties of Pictou
and Antigonish, Nova Scotia, which seems to make a slow extension from
farm to farm, but does not spread widely after the manner of a disease
propagated by contagion alone, apart from other concurrent causes.
_Alleged Causes._ E. F. Thayer (1880) tells us that the inhabitants
traced its origin to the arrival from Scotland, about 1853, of a ship in
earth ballast, containing the seeds of the common ragweed of Europe
(Ambrosia Artemisiæfolia), alleging that the trouble extended with the
extension of this weed. This plant has a strong odor (it is known in
Pictou as “Stinking Willie”), and, like other plants shedding an
abundance of odoriferous pollen, has been charged with arousing “hay
fever,” but though very common in Europe it has never been charged with
producing anything like the Pictou cattle disease. The coincidence of
the plant and the disease is manifestly a mere accident. Professor
Lawson, of Halifax, investigated the flora of the district but was
unable to find any poisonous plant to which the mortality could be
attributed. D. McEachran tells us that many farms are covered with the
ragweed, so that it is abundant in the hay, yet they are absolutely free
from the disease.
The idea of a mineral poison must be dismissed in the same way. Pictou
lies on the Silurian formation with abundant coal fields, and the
chemical analyses made for McEachran were entirely fruitless of results.
Wyatt Johnston investigated the question of communicability by contagion
from animal to animal, but he found that neither contact, nor
inoculation produced positive results. Nothing positive has come of
investigations into the possible microbiology of the disease. In blood
from the jugular vein of a cow suffering from the disease, Thayer and
McEachran found bacteria, under an object glass magnifying 600
diameters. Wyatt Johnston, “in a series of pretty exhaustive
bacteriological examinations, in which all the tissues, including the
blood, the spleen, the kidneys, lungs, and the fluids from the lymph
glands” were employed, failed to find any constant or characteristic
organism.
Attacks are very rare in winter, the disease usually appearing in the
warm summer months, from June to August, and after the animals have been
some time at pasture. This might lead to the suspicion of bacteria or
other microbe on the growing vegetation; or of some insect enemy which,
maturing at that season, transfers the poison from animal or other
source to animal; or of some poison, vegetable or mineral, which acts
injuriously on the liver, and which can only be had in the pasture.
This, however, is mere hypothesis.
Liver affections are common in hot, damp seasons, but Pictou and
Antigonish do not differ in climate from other counties in Nova Scotia,
and much less do the infecting farms from those adjacent.
McEachran compares the disease to what occurs in the human being during
famines, from the ingestion of innutritious and unsuitable agents
especially deficient in albuminoids. The Pictou farmers, being nearly
all fishermen, neglect the farms during the summer season, so that hay
is only cut after the seeds have been shed, and when little nutritive
matter is left in the stalks. Almost all the cases he saw were on such
neglected farms. Wyatt Johnston, however, found it equally prevalent in
overfed animals, so that hepatic disorder from either extreme seems to
conduce to it. Again, if caused by lack of nutrition in the hay, winter,
rather than summer, ought to be the season of attack and prevalence.
Starvation and excess may both favor the attack, but the gradual
extension from farm to farm, is strongly suggestive of the presence of a
specific cause—probably a living organism.
The limitation of the disease to certain farms and even fields, and the
cirrhotic condition of the liver remind one of the Schweinsberg disease
of horses, and the lupinosis of sheep, in which the poison is evidently
the product of cryptogamic or bacterial growth. With the damp, foggy
climate of Nova Scotia, it would not be surprising if it should be
ultimately shown that the source of the trouble is in a cryptogam which
has as yet only invaded a given limited area. The winter immunity would
be explainable on this basis. So also would be the statement of Wyatt
Johnston that “When it attacks a new farm it affects chiefly animals
that have been on the farm for two or three years. By the end of the
second year it kills or attacks 10 per cent., and by the end of the
third season it has practically involved all the old cattle which have
been allowed to remain on the farm.” The hepatic disorder being a
progressive one and probably due to the toxic products of fermentations
carried on outside the animal body, a few only would show the morbid
results at first, while later, with advancing structural changes in the
liver, and an increase of the toxins that cause it, the number of sick
animals would steadily increase.
_Symptoms._ The animal is at first dull and sluggish, with drooping
head, lusterless eyes, staring coat, normal respiration and temperature,
pulse often about 60 per minute, relaxed bowels and marked diminution of
the milk secretion. The milk acquires a bitter taste and unpleasant
odor. The pulse is usually full and soft, and the eyeballs may bulge
visibly out of the sockets. The diarrhœa tends to encrease, the stools
becoming liquid and black, yet in exceptional cases the bowels are
confined for the first four or five days, or even permanently, appearing
to be completely paretic. By the end of a week the abdomen becomes full
and pendent with hollow flanks (pot bellied), or even rounded and tense,
while manipulation and percussion show an abundant exudation into the
peritoneal cavity. The pulse encreases in frequency (80) but the
temperature is not elevated unless there is concurrent sepsis
(Johnston). Thayer quotes an advanced case with a temperature of 105° F.
He also notes obstinate standing, trembling of the muscles of the hind
limbs, and complete suppression of appetite and milk secretion.
The disease is essentially chronic, often lasting a number of months.
Many cases are doubtless slightly affected before external symptoms are
manifested.
_Lesions._ If the disease has resulted in death there is usually marked
emaciation, yet the abdomen is distended by accumulation of a clear
yellowish fluid. From six to nine or more gallons may be present. The
fat of the omentum, mesentery and sublumbar region has disappeared and
the connective tissue is distended by a clear, amber-colored, watery
fluid. The liver is the seat of marked changes. In the early stages it
is congested and the gall ducts and bladder are filled to repletion with
a thick, dark colored bile, which is further present in abundance in the
intestines. In these early stages Johnston found cloudy swelling and
opacity of the hepatic cells; somewhat later they had undergone distinct
fatty degeneration. In the advanced stages, however, in animals that had
been ill for two or three months, there was distinct fibrous
degeneration, and compression and disappearance of the normal liver
cells, in other words, a condition of marked cirrhosis, the result
doubtless of the early congestion.
Johnston further notes the distension of the submucosa of the fourth
stomach at intervals by a clear, viscid, liquid exudate, so that rounded
swellings appear on the surface, and in some instances, after a month’s
illness, distinct ulcers are shown upon the mucosa.
The lungs, pleuræ, pericardium and nervous system, are usually normal,
unless in case of septic complication when petechiæ and circumscribed
blood extravasations may be seen.
_Prevention._ The Canadian government has gone to great expense in
buying and slaughtering the diseased cattle with no very evident good
result. McEachran suggested the feeding of oil cake and other albuminoid
and oleaginous food to counteract the alleged malnutrition, but
Johnston’s cases in over fed animals show that something more is
demanded. Another suggestion has been made to the effect that cattle
should be exterminated in the affected counties to remove the material
necessary for the maintenance of the poison. But, if the poison is
produced by a cryptogam growing on the vegetation, as seems not
improbable, it would be likely to extend all the same in the absence of
cattle. In such a case the true course is to study the nature of the
organism, and the phanerogam on which it grows, when it might become
possible either to exterminate the flowering plant which acts as a host
for the offending organism, or to spray it with an effective fungicide
and thus reach the object in another way.