This is manifestly the same disease, and due to the same microbe as
horse pox. The disease of the one genus is easily transmitted to the
other and the lesions and symptoms are the same, as if the virus were
derived from an animal of the same species. Differences in the local
manifestations appear to be due rather to the varying conditions of the
skin and hair follicles, than to any material distinction in the virus.
_Causes._ Aside from the germ (Sporidium vaccinale) the conditions which
favor infection are: the milking of susceptible cows with imperfectly
washed hands, after dressing legs, the seat of horse pox eruption; the
milking of healthy cows after those affected with cowpox; and the
milking with hands contaminated with the exudate in cases of vaccination
of man. That susceptible cows may also be inoculated successfully from
smallpox patients, under given conditions appears to be true, but in
Western Europe and America this is very uncommon, and would be much more
so if vaccination were universally carried out. Among those who claim
the identity of small pox and cow pox may be named Ceely, Reiter,
Babcock, Thiele, Voigt and Klein.
Ceely alleges the infection of five cows and one heifer, in 1839, in
England, from chewing the flock of a bed on which a small pox patient
had died. In 12 or 14 days they had tender congested udders, with hard
pimples imbedded in the skin, followed by blisters, and brownish scabs.
The milk diminished, saliva drivelled from the mouth, the cheeks were
inflated and retracted, the coat stared, their feet were drawn together,
and the back was arched. The disease was communicated to the owner. This
was clearly an outbreak of aphthous fever, which invaded England in that
year, and was still an unknown disease to medical men. The implication
of the heifer which would not have been inoculated with variola through
the hands of the milker, and the salivation which is unknown in cow pox,
but points directly to the buccal vesicles of foot and mouth disease,
are conclusive on this point.
Ceely later, after many fruitless attempts to convey smallpox to the
cow, at last met with results which indicated cowpox, and which he
thereafter passed from cow to cow with the characteristic cowpox
eruption.
Fletcher further reports the transmission of smallpox through the horse
to the cow, and thence to the child in the form of cowpox.
In 1836, Thiele, Kasan, S. Russia inoculated some cows on the udder with
smallpox lymph, and conveyed the lymph of the resulting vesicles back to
man, and from man to man for seventy-five generations of the virus
without finding any variation from the type of the true vaccine disease.
He repeated the experiment with equal success in 1838.
Such experiments, made before the days of careful antiseptic, or
aseptic, laboratory methods, by men who were daily engaged in making
vaccinations, cannot be very implicitly relied on, yet the success of
Thiele in Central Asia, the early home of variola, may indicate the
possibility of a transition, under given eastern conditions, which, to
say the least, is exceedingly rare in Western Europe or America.
The experiments of Klein, conducted under modern methods, are more
conclusive, and seem to imply the possibility of smallpox passing into
cowpox, in the bovine system, under some not yet clearly defined
conditions. Until such conditions are sufficiently well known, so that
they can be controlled at will, no one can be justified in attempting to
produce lymph for vaccination by simply passing smallpox virus through
the system of the cow.
It seems important to note one or two instances of the evident
transmission of smallpox from man to man through the bovine system.
In 1860, Martin inoculated variolous matter, from a man who had just
died of smallpox, on a cow’s udder, and subsequently inoculated about
fifty persons from the eruption caused in the cow. Most of those so
inoculated had unmistakable smallpox and three died.
Reiter had a very similar experience.
Chauveau (French Commission) inoculated twelve susceptible cattle with
smallpox virus and produced, in all but one, small conical (smallpox)
papules and vesicles, and in ten of these, on subsequent inoculation
with cowpox, six proved immune, three had rudimentary pustules, and one
had a distinct cowpox eruption.
A milch cow and two heifers were inoculated with smallpox and cowpox on
two sides of the vulva, with the result that each disease appeared in
the seat of its inoculation, with its characteristic vesicles, and the
two developed side by side. The smallpox vesicles were by inoculation
conveyed from ox to ox with steadily decreasing activity. Inoculated
from the cow on a child, it caused great hyperthermia, vomiting, one
large vesicle like vaccinia and a general eruption like varioloid.
Inoculation from this child upon another produced a mixed eruption of
cowpox and varioloid. Inoculation from the second child on a bull and
heifer produced papular eruption only.
Smallpox virus, inoculated on a horse produced a papular eruption, but
failed to affect another horse that had been previously vaccinated.
Cowpox virus inoculated on the first horse which had had the papular
eruption, caused a second papular eruption (not cowpox). The virus from
a vesicle in the first horse caused a similar eruption in another horse,
on which it was inoculated. The lymph from the papular eruption led to a
similar eruption in cattle, on which it was inoculated, but did not
protect against cowpox, subsequently inoculated.
The lymph from the papular eruption in the horse, inoculated on two
children, produced fever, vomiting, a general papular (smallpox)
eruption, in which a few of the pustules only showed a tendency to
umbilication. A child and its mother in the same ward contracted
varioloid. A child inoculated from one of the first named children, had
six large umbilicated vesicles like cowpox and a general papular
(smallpox) eruption. Another child inoculated from the last had six
large umbilicated vesicles, and a general papular (smallpox) eruption.
From the papular eruption of one of these children a horse and seven
cattle were inoculated and in all a varioloid eruption resulted.
The rational conclusion is, that while there is every indication of a
primal identity of the two diseases, and indeed of all forms of variola,
as shown by a disposition of the virus from one genus, when inoculated
upon a totally different genus, to show some indication of the
characteristic eruption of the latter, yet the generic type, which comes
from the long continued growth in the one class of animal, becomes so
fixed, that it cannot be overcome at once, and sometimes apparently not
at all, by transferring it to an animal of another class.
If the unfortunate results obtained by Martin, Reiter, and Chauveau, are
insufficient to deter from the use of smallpox lymph which has been
passed through the cow, the long experience with humanized vaccine,
which in its inoculation from man to man for a century has shown no
tendency to revert to smallpox virus should be a sufficient warning
against such dangerous optimism.
No deduction can be safely drawn from the comparative mildness of most
of the cases caused by reinoculation from cow or horse to man, inasmuch
as that all forms of variola can be rendered less severe by resorting to
inoculation, which was extensively practised to limit the ravages of
smallpox before the days of vaccination, and is still largely resorted
to in the case of sheeppox in Europe. In each of these diseases the
mortality can easily be reduced to 2 per cent. instead of the 20 to 50
per cent. which are lost when the disease is contracted casually.
As occurring casually, cowpox like horsepox is rare. Yet in Denmark, a
dairying country, 1,037 cases were reported in 1877–8, and 878 cases in
1888–9. I have found some outbreaks explainable, through the existence
of vaccinations in the families of the milkers, and Bollinger says that
in Germany, most outbreaks take place in spring, the time when children
are vaccinated. He should have added that this is the usual time of
parturition in the cow, the time when primipara are first subjected to
the danger from the hands of the milker, and when the cow from the
noninfected district is brought into an infected stable for the season’s
milking. In a dairying district in Tompkins Co., N.Y., the affection
appeared every spring, in the same barns, in heifers with their first
calf and in newly bought cows. All older cows, bulls, steers and
unimpregnated heifers escaped.
_Symptoms._ The period of incubation is two days, after inoculation, and
though it may appear to extend to a week when the disease is contracted
accidently, it is impossible in such cases to state the exact date of
infection. The preliminary fever is not always present, or recognized,
yet there may be slight encrease of temperature, partial impairment of
appetite and rumination, extra firmness of the fæces, a higher color of
the urine, and above all a slight diminution of milk, which is a little
more watery and coagulates more readily, than the normal.
This is followed by heat and tenderness of the udder and the appearance
on the teats of small, pale red nodules the size of a pea or larger. In
one or two days more the nodule, largely encreased in size, presents in
the centre a depressed or _umbilicated_ bluish white portion, with a
firm yellowish, reddish or reddish blue margin, and outside this a soft
pink areola, shading off into the white skin. The epidermis is raised at
points by a viscid, yellowish lymph, enclosed in a series of saccules
(multilocular vesicle). The vesicle encreases to 8 or 10 lines in
diameter by the eighth or tenth day, and exceptionally, the umbilication
is effaced by the excessive production of lymph. If left unbroken a
brownish shade appears in the centre and gradually extends toward the
periphery, the contents becoming purulent, and the pustule gradually
drying up to form a crust. The drying and thickening of the crust goes
on until the fourteenth day and the crust is usually detached by the
twentieth, leaving a pale rose colored, smooth, shallow depression,
which forms the permanent pit left after the skin has healed. The
primary scabs usually show the central umbilication, and always the
conical projection in the center of the deep aspect, and corresponding
to the pit.
Vesicles on the mammæ may pass through the above stages, but those on
the teats are usually ruptured by the hands of the milker as soon as the
liquid is thrown out, and this gives rise to troublesome sores, with
complex infections, at times implicating the gland tissue so as to cause
destructive mammitis with loss of one or more quarters, and in any case
abraded and irritated at each milking, so that the animal resists
handling, the milk is drawn off imperfectly, and dries up or the cow
becomes an inveterate kicker. If the milker has not been vaccinated he
is liable to contract the disease.
A succession of vesicles often appear on the same animal, so that they
may be found in all different stages of vesicle, pustule and crust on
the same bag at one time. The later eruptions may be the result of
inoculation from the earlier ones, and tend to prolong the attack
materially.
In inoculation of the bovine animal for the production of lymph for
vaccination, the skin of the abdomen from the symphysis pubis to the
umbilicus is shaved, or in other cases the skin between the thighs, or
in still others the skin on each side over the loins, and the virus
applied in 50 to 200 points, by preference scraped until liquid oozes,
but without any escape of blood. In a warm room the eruption matures in
four or five days, its form taking on an appearance approximating that
seen on the hairy skin of the horse. The individual lesions are somewhat
extended corresponding in form and size to the abrasion on which the
lymph was applied, and usually present the appearance of a raised patch,
covered by a grayish film of epidermis, on the removal of which there is
seen a raw alveolated surface filled with the amber-colored lymph.
_Differential Diagnosis._ From _aphthous fever_, cowpox is clearly
distinguished by (a) the multilocular structure of the vesicle, while
that of aphthous fever is a single undivided cavity which can be drained
completely by a single needle prick; (b) by the pitting or umbilication,
the aphthous vesicle being uniformly rounded and convex; (c) by the
absence of vesicles or sores on the mouth and feet, which are rarely
wanting in the aphthous eruption; (d) by the comparative absence of
hyperthermia and constitutional disturbance, which is better marked
though still slight in aphthous fever, and (e) by the absence of the
intense and subtle infection of aphthous fever, which quickly attacks a
whole herd and extends with equal rapidity over sheep, goats and pigs,
attacking all cloven-footed animals virtually without exception. The
cowpox patient, on the contrary, does not necessarily attack the cow in
the next stall unless milked by the same hands, and spares heifers,
bulls, steers, sheep, goats and pigs.
From the _rinderpest_ cutaneous eruption it is easily distinguished by
the presence of lymph in the lesion, that of rinderpest being a mere
epidermic concretion; by the absence of the intense fever, anorexia and
general constitutional disturbance, and of the early and high mortality
which characterize that disease; by the absence of rapid and uniform
infection of other cattle irrespective of a common milker; by the
immunity of heifers, steers and bulls, which are speedily prostrated by
rinderpest, and by the absence of the congestions and epithelial
concretions of the mucosæ which characterize rinderpest.
From the _leg irruption_ found in animals feeding on distiller’s swill
and grains, or on the mast of beet sugar factories, by the history of
the outbreak, of the dietary, of the seat and nature of the disease, and
by the escape of animals living on a different aliment.
From the _false cowpox_ (varicella) it is distinguished by the
unilocular lesion of the latter, its absence of areola, and its rapid
pustulation and drying, in five or six days into a thin papery crust
instead of a thick, firm, umbilicated scab, as in cowpox. Varicella is
further liable to appear in successive crops and thus last for several
weeks.
The _streptococcus eruption_ on teats and udder, is marked by the
formation of abscesses of various sizes from a simple pustule upward, by
the unilocular condition of the pus sac, by its tendency to invade the
deeper tissues, and by its rupture and granulation without the formation
of the thick umbilicated scab of cowpox.
The _hard warty growths_ on the teats which last for weeks or months
should never be mistaken for cowpox.
_Cowpox_ usually lasts for some weeks in a herd, the duration depending
on the number of susceptible animals and, whether these are habitually
milked by the same person.
_Course. Prognosis._ It is a mild affection, which does not endanger
life, yet it causes considerable loss through diminution of the milk
secretion and, it may be, altered character of the milk, through the
persistent sores and ulcers of the teats, through inflammation of the
mammæ, and through an acquired habit of kicking.
_Treatment_ is rarely needed. Any costiveness should be corrected by a
cooling saline laxative (½ to 1 lb. Epsom salts) or by soft food, and
milking should be done with great care to prevent rupture of the
vesicles and the formation of sores. A teat tube may be used if
necessary. Sores may be dressed with bland ointment. An ounce each of
spermacetti and sweet almond oil with half a dram of gum myrrh. Or the
vesicles or sores may be washed after each milking with a solution of 2
drams hyposulphite of soda in 1 quart water.