_Synonyms._ Pocks; Peltrot; Clavelee, Picotte, (Fr.).
_Definition._ An acute febrile affection, eminently contagious,
prevailing epizoötically in sheep and goats, characterized by early and
marked hyperthermia, and general constitutional disorder, followed by
the appearance on the bare or merely hairy portions of the skin, of
diffuse redness becoming intensified in points, a rounded papular
eruption, passing into vesicles, pustules and scabs, which latter dry up
and drop off in 15 to 20 days.
_Pathogenesis._ Beside sheep and goats which contract the disease by
exposure, the following genera have been successfully inoculated: ox,
dog, pig, horse.
_Forms._ Two typical forms are recognized: (_a_) the _discrete_,
_regular_ or _benign_, in which the vesicles remain relatively few, and
well isolated from each other, and (_b_) the _confluent_, _irregular_ or
_malignant_ in which the vesicles are generally diffused over the body,
even on the parts covered by wool, and set so close together that they
merge into each other forming extensive continuous lesions. Other forms
are the _hæmorrhagic_, _purple_ or _black sheeppox_, the volante or
intermittent kind, etc.
_Geographical Distribution._ Formerly common in Central and Western
Europe, it still prevails continuously in the Balkans, the Danubian
Principalities, Italy, Spain, the South of France and Algiers. Like
other forms of variola, its permanent home is in Asia.
_Causes._ Long before the advent of modern bacteriology, sheeppox was
held to be always and everywhere the result of contagion alone. Whenever
it entered a new locality it was as the result of the importation of an
affected sheep or one of its products; insular places like England
maintained a permanent immunity, though the disease prevailed on the
other side of the narrow straits or channel; yet when imported (1847 and
1862) it demonstrated a general susceptibility of the flocks on exposure
or inoculation; more distant lands (America, Australia, Tasmania, South
Africa, etc.) in the absence of imported infection remain clear to the
present day.
The infection is more intense and diffusible than that of cowpox and
horsepox following in this the smallpox of man. Absolute contact is not
necessary, in either case the infection is carried in the air either on
dust or otherwise, and above all in a confined building, a crowded sheep
fold or a dusty highway.
In all forms of variola the virulence is concentrated in the lymph of
the vesicle, and in horsepox and cowpox it is largely confined to this,
whilst in sheeppox in severe cases it must also at times infect the
blood, as lambs are occasionally born with sheeppox. On this basis the
infection of the secretions generally has been advocated, but it is to
be supposed that in moderate cases these are contaminated after
secretion. Nocard and Roux produced immunity by the transfusion of blood
from the sick to the healthy, but in no case a variolous eruption. Even
the serosity from the swollen lymph glands failed to convey the disease.
In view of the diffusible nature of the germ, however, we must recognize
that all secretions may be quickly contaminated as soon as they are
exposed, and therefore no product of a sick or suspected sheep can be
held to be safe, and all should be treated as presumably infected. The
most dangerous products and those most liable to convey the disease are
wool, hides, litter, buildings, yards, covers, parks, railway cars,
boats, manure, urine and milk.
Living creatures like men, dogs, cats, birds, vermin, flies and other
predacious insects are occasional bearers of infection.
_Receptivity_ must be considered in every case. In countries and
districts habitually immune from sheeppox, all breeds appear to be
equally susceptible, the only refractory specimens being sheep that have
survived a first attack, and lambs born of ewes that had the disease
(naturally or inoculated) during the later stages of gestation. New born
lambs, on an exclusively milk diet, are alleged to be somewhat
refractory. In a country where sheeppox has prevailed long and
extensively, as in Algiers and Brittany, certain breeds of sheep seem to
have attained to a large measure of immunity (Nocard). This is doubtless
largely due to the survival of the more insusceptible strains of blood,
as Algerian sheep carried into France lead to most virulent outbreaks
among the native animals (Galtier).
This relative immunity is still more decided when we come to animals of
other genera. Though the latest results of research seem to identify the
sporidia found in the different forms of variola, yet the long habit of
living in an environment found in the ovine race unfits the germ for
pathogenic life in various other genera that have their own variolæ.
Sacco and Villain reported inoculations from sheep to man, but as the
first was experimenting with variola at the same time, and the second
did not test his pustules by reinoculation the results are not
convincing. Küchenmeister had a general eruption in sheep after
intravenous injection of variola of man, but failed to test it by
reinoculation. Voisin and Nocard on the other hand were uniformly
unsuccessful in attempts to convey sheeppox to man, and the handling of
variolous flocks from time immemorial must have led to many cases in
man, had he been appreciably receptive. It is virtually the same with
cowpox. Huzard vaccinated 2,000 sheep without producing immunity from
sheeppox. Voisin had precisely similar results. He further inoculated
infants with sheeppox, and later, successfully, with vaccine lymph.
It does not follow that these genera would be insusceptible under all
conditions. Yet the failure to immunize against each other would argue a
wider divergence of sheeppox and cowpox, than of smallpox and cowpox, or
than of bovine and avian tuberculosis.
Galtier failed to inoculate sheeppox on rabbits or Guinea pigs, yet
Jourdan, records a destructive outbreak in the Alps, in hares, kept in
the same places with variolous sheep.
_Accessory External Causes._ All unwholesome conditions of life, and
especially overcrowding, filth, starvation, and neglect contribute to
the extension of the infection. Still more so, the importation of sheep,
whether in the parks of armies, or in the channels of trade, by rail, or
steamboat, through stockyards or markets.
The virus is possessed of unusual vitality, and in the dried condition,
secluded from air and light will remain virulent for an indefinite
period. Hence the danger of wool, and dried sheepskins. Even in the
moisture of an ordinary shed it has retained its infectiveness for five
or six months. The sheep that has recovered from the affection may
transmit the disease to others for a period of six weeks. The virulence
is rapidly destroyed by exposure to free air and sunshine, by a high
temperature (140° F.), by dilute HCl (2:100), by carbolic acid (2:100),
by zinc chloride (5:100), by potassæ permanganas (10:100), by lime
chloride (4:100), or indeed by any of the strong antiseptics.
_Incubation._ This extends from four to seven days on an average, with a
minimum of two and a maximum of twenty days. The conditions favoring an
early eruption are youth, high condition, and a hot season, or close
warm building, with overcrowding. Those favoring a tardy eruption are
old age, debility, and above all a cold or wet season with exposure in
the open air. Simonds, who inoculated in England in the cold months
(October and November) never saw it exceed 13 days. In certain cases,
however when the eruption had already commenced in mild weather, the
sudden occurrence of a week of cold and wet, would stop it short to
start anew on the return of warm weather a week later. In inoculated
cases the incubation is shortened, while it is prolonged when the virus
is introduced by the digestive or respiratory passages.
_Symptoms._ During the last two or three days of a prolonged incubation
and especially in old sheep, there may be some impairment of appetite
and rumination, dulness, a stiffness of movement of the hind limbs, and
a disposition to lag behind the flock. The temperature may even have
risen (104.5° F.), yet Simonds has never seen the febrile symptoms
precede the eruption.
There follow, trembling, or rigors, accelerated pulse (80 to 90) and
breathing, arched back, anorexia, suspension of rumination, costiveness,
redness of the eyes, epiphora, a watery discharge from the nose,
gradually becoming more viscid, and a marked hyperthermia (105°, 106° or
107° F.) If the skin is white, a blush, with some heat, is shown in the
seat of the future eruption, usually on the parts uncovered by wool, the
axillæ, sternum, abdomen, udder, inner sides of the thighs, lower
surface of the tail, and the face—especially the eyelids, nostrils and
lips.
In two days more, deep red points, like flea bites, appear more or less
numerously, in the congested parts of the skin, and in twenty-four hours
these have increased to firm rounded papules which are felt to extend
into the true skin. These vary in size from 3 to 12 mm. or more. In two
or three days the papule has become firmer and less tender, and shows in
the centre a paler area where the exudation has resolved it into a
vesicle. The characteristic sheeppox vesicle is rounded or flattened on
its summit, being rarely pointed as in smallpox, or umbilicated as in
cowpox. It is usually surrounded by a pink zone, which is at times
infiltrated, firm and resistant. After about the sixth day, the vesicle
becomes yellowish from the formation of pus. The pustules, with the
surrounding tumefaction, encrease for about three days, when if they
have not become confluent nor infected, they begin to dry up, acquiring
a grayish crust on the surface which gradually encreases to a thick
scab, which in five or six days more is detached leaving a pink, pitted
spot covered by forming epidermis. Sometimes no distinct scab forms, but
the crust dries, cracks up, and falls off in scales.
All the vesicles do not appear at once, but some earlier and some later,
so that the successive stages of the eruption may be often seen together
on the same subject, and the case is thereby materially prolonged.
As in other forms of variola the hyperthermia usually subsides with the
appearance of the eruption, but as often reappears in some measure with
pustulation (secondary fever of reaction), and becomes more severe in
proportion to the extent and confluence of the eruption and the
occurrence of complex infection.
The eruption may invade the conjunctiva, the cornea (inducing
blindness), the nasal mucosa (causing difficult breathing), the mouth
(salivation, difficult mastication), the pharynx (difficult
deglutition), the stomach and intestines (diarrhœa), the bronchia
(cough), or the vulva.
With the occurrence of desiccation, in discrete cases, the fever
subsides, the swelling of the skin and head disappears, the discharges
from the nose and eyes cease, and the animal is restored to health.
A secondary eruption will sometimes take place, but only papules form,
which disappear without reaching maturity.
The duration of discrete sheep pox is usually about three weeks, but it
may reach four in cool weather. It is more rapid and more prone to
dangerous complications in hot weather. As the members of a flock are
usually attacked in succession, it may take three months to pass through
a flock.
In _confluent_ or _complicated cases_ the fever of invasion is very
high, the sheep dull, prostrate, tender to touch along the back and
loins particularly, with hurried, labored, panting, breathing, and
mawkish, fevered breath, the weakness increases rapidly, standing even
may become difficult, the wool is loosened and falls off in patches, the
exposed skin is red, shading, it may be, into a violet hue. The head
droops, the lips and nostrils swell, saliva drivels abundantly, anorexia
is complete, though thirst may be ardent, a yellowish and even reddish,
fœtid discharge may flow from the nose, respiration is difficult, the
eyes are watery and deeply sunken, and the head, limbs, breast and
abdomen are extensively infiltrated and œdematous.
Fever does not subside with the occurrence of eruption, which may appear
thickly over the whole body, the woolly parts as well as the bare or
hairy. The vesicles, which have often a dark, unhealthy look, tend to
become confluent, and instead of proceeding regularly to maturity, they
may remain hard or indolent papules or nodules or blacken and dry up.
The secretion, when it takes place, is liable to be a thick, yellowish,
fœtid pus. The eruption has much more tendency than with the discrete
form to invade mucosæ, and not infrequently the serosæ are involved,
especially those covering the lungs, liver and spleen. In the worst
cases death may result from the fever before any eruption has taken
place, in other cases the extent of the internal lesions tends to hasten
a fatal result. With the amount of care that can be given to a flock,
confluent cases are usually fatal.
In connection with the itching and scratching of the nose, abrasions and
complex infections ensue, resulting in extensive ulceration and gangrene
implicating the nasal cartilages and bones. The eruption around the
pasterns may lead to shedding of the hoofs, and sloughing of the whole
digital structures. Suppurating and gangrenous swellings form
subcutaneously and in the lymph glands with fatal results. Blindness is
especially liable to happen from the formation of the eruption on the
conjunctiva and cornea. Ulcerations and sloughs are common on the
internal mucosæ, and even on the serosæ. In implication of the abdominal
organs, a fœtid diarrhœa is usually present, and in pregnant ewes
abortion is the usual result.
_Lesions._ The cutaneous lesions are in their multilocular structure,
the same as in cowpox, but differ materially in size and form. The
typical vesicle is small (5 to 12 mm.), and neither broad and
umbilicated like cowpox, nor conical and pointed as in smallpox, but
round with a slight flattening on the summit. On the same animal may
often be found all the successive stages at once, red points or
hæmorrhagic spots, vesiculation, pustulation and even desiccation. The
early changes are seen in the papillary layer and rete mucosum, in the
form of swelling and congestion of the papillæ, exudation, active
proliferation of the epidermic and tissue cells, and migration of
leucocytes, (embryonic cells polynuclear) vacuolation of the papule, the
spaces being filled with a straw colored exudate, and finally, the
replacing of this by pus. If the local inflammation is very acute, the
pustule may be resolved into a small abscess. On section of the skin the
affected parts are found to be the seat of congestion and gelatinoid
exudation, extending into the subcutaneous and intermuscular connective
tissue, and even the muscles themselves are blackish and their
capillaries engorged. The exudation is especially abundant in the
dependent parts (head, neck, sternal and abdominal regions, legs). In
proportion to the severity of the attack there are congestion,
exudation, swelling, and blood extravasation in the lymph glands.
The nasal mucosa is congested, thickened or even ulcerated with
abundant, tenacious, muco-purulent secretion and the nasal chambers
narrowed or obstructed, and similar changes may be present in the
larynx, trachea and bronchia. Spots of ecchymosis and even distinct
variolous vesicles are to be expected. The pleuræ are often the seat of
congestion, petechiæ, exudation, and discoloration (red or pale). The
lung may show congestion and hepatisation in circumscribed areas, or
there may be on the surface of such hepatised portions red or grayish
foci, like a lentil, pea or bean, the seat of degeneration or forming
minute abscesses. The pericardium and myocardium may be involved to a
limited extent.
The buccal and pharyngeal mucosæ may be the seats of vesicles, or
erosions or ulcers the result of their destruction, and the
gastro-intestinal mucosa presents ecchymoses, vesicles, abrasions, and
open sores in the midst of inflamed catarrhal patches. The mesenteric
and other lymph glands are congested, swollen, softened and friable.
Congestions and petechiæ are found on the peritoneum, liver, spleen and
kidneys, with, at times, nodular foci. In certain cases congestions and
effusions have been found on the pia mater and arachnoid, in the
cerebral ventricles and the brain substance.
_Prognosis._ _Mortality._ Mortality varies much with the severity of the
special outbreak and the conditions of life, favorable or otherwise, in
which the flock is placed. In the milder forms the mortality may not
exceed seven per cent, while in the more violent the whole flock almost
may perish. A fatality of 20 to 30 per cent is the general average. Yet
the inoculated form kills but 2 per cent.
If at the outset there is great weakness and prostration, complete
anorexia and high fever, the prospect is discouraging. If the fever is
moderate and strength and appetite retained, the case is very hopeful.
On its first advent into a new country it causes a far greater mortality
than after it has been long domiciled there, and frequent outbreaks have
killed off the more susceptible strains of blood. Again very hot
weather, or, still more, the prevalence of cold, drenching rains
aggravates an outbreak and greatly encreases the fatality.
The loss is not to be measured by the deaths alone. The failure of the
crop of lambs, through abortion, the shedding of wool, the loss of
sight, hearing, hoofs, digits, flesh, stamina, etc, render recovery far
from desirable, in the worst cases, as the animal fails to thrive or pay
for its keep. On the contrary it is immune from any future attack, and
if left in a thrifty condition it becomes especially valuable in a
district where sheeppox prevails.
_Treatment._ Once established in the system the disease will follow its
regular course, through all its stages. Yet we can, by dieting, pure
air, cleanliness, shelter and even by medicinal measures, do much to
render that course a safe one. Cool sheds, pure air, clean floor, dry
clean litter and shelter from rain are above all important. The sheep
may be separated in different enclosures in small lots of 5 or 6 to
prevent crowding, heating, and excitement, and in any case the infected
should be removed from the noninfected, and even from each other to
avoid infection and reinfection. This is especially requisite in hot
weather.
For the strong and vigorous, a diet of sliced roots and meal (oat, bran,
linseed, barley, wheat middlings) is good, while for the weak, gruels of
oat meal, barley meal, linseed meal, or the same agents dry, may be
given. Powdered saltpeter may be given in this (1 oz. to 8 or 10 sheep)
and common salt allowed to be licked at will. Drinking water may be
given pure, or slightly acidulated with sulphuric or hydrochloric acid,
or hyposulphite or bisulphite of soda may be used as a substitute for
the latter. The bowels are usually costive, and may be relieved at first
by 3 ozs. of sodic sulphate, and later, if need be, by soapy injections.
Often during the course of the disease a sudden access of fever may be
cut short by a mild laxative, if that is not contra-indicated by
existing diarrhœa.
Avoid giving heating agents to bring out the eruption. The severity of
any case and the danger of complex infection are usually in ratio with
the extent of the eruption.
Lotions of hyposulphite of soda may be applied to the affected parts
from the first, and even weak lotions of chloride of zinc after the
maturation of the pustules. For the eyes, nose and mouth antiseptic
lotions may be called for.
In the advanced stages, in weak subjects, tonics and stimulants may
prove useful. To the mineral acid, quinine (10 grain doses) or gentian
(drachm doses) or other bitter may be added for valuable stock.
Treatment is only permissible in the case of very valuable animals and
when they are surrounded with the most perfect antiseptic precautions,
to prevent the escape of the infection.
_Prevention._ As in all dangerous infections this must be the preëminent
object, and when a new country has been invaded by the disease, no
sentiment nor alleged value of affected or exposed animals should be
made the warrant for treatment, nor stand in the way of the extinction
of the plague by the most rigorous measures. The recovery of an
individual flock is never to be put in the balance with the danger to
which other flocks are thereby exposed. To avoid smuggling away of
exposed animals, and consequent spread of the disease, the loss should
be met by the commonwealth and no foolish idea of administrative
economy, should tempt a stock owner to endanger the flocks of a whole
nation.
Sheep and goats from countries where sheeppox exists should be
absolutely excluded. If, in exceptional cases they are allowed to land
on our shores, they should be guaranteed by a veterinary certificate as
coming from a noninfected district, by a route free of infection, they
should be critically examined by an expert on arrival, and if passed,
should still with all clothing and utensils, be subjected to thorough
disinfection. The clothing of attendants should be similarly dealt with.
If importation is merely across a frontier, a quarantine of 21 days
followed by a disinfectant bath should be enforced.
If sheeppox has gained a footing in a flock in a new country, the flock
should be at once appraised and destroyed, and the place thoroughly
disinfected and shut up for three months. All cars, ships, wharfs,
landings, chutes, yards, buildings, parks, roads, etc., used by them
should be closed and thoroughly disinfected. All flocks exposed to any
such place or thing should be placed in strict quarantine for three
weeks, under official veterinary supervision and disposed of, should
they become affected.
As an alternative each infected and suspected flock should be secluded
in a well fenced place or shed from which all men except the necessary
attendants, all dogs and other mammals, including vermin, all birds and
as far as possible all flies are excluded. They should be divided into
small lots of 5 or 6 placed in separate pens, their temperatures should
be taken 3 or 4 times a day, and any one showing a temperature of 104°
or 105° F. should be instantly removed to a separate pen, and destroyed
as soon as the disease can be identified. In this way a diseased sheep
can usually be removed before it has infected its fellows, and at the
worst the infection will rarely spread beyond the 5 or 6 animals
enclosed in the pen where the first case appeared. It is well to
sprinkle the wool of all the flock with a 5 per cent solution of
carbolic acid, and the floor or ground with chloride of lime. The
diseased carcasses should be thoroughly sterilized by burning, boiling,
or immersion in strong acids, or they should be deeply buried, the
infected pen disinfected on each occasion, and the hands and clothes of
the attendants purified.
Careful treatment in this way will usually cut short the disease with
the loss of those only that were already infected when the outbreak was
taken in hand, but it must be in the hands of men who are at once
experts and vigilant and trustworthy. The English invasion of 1862,
under the direction of the late Professor Gamgee, was completely stamped
out in four weeks on this plan, whereas the invasion of 1847, met by the
expedients of inoculation and quarantine, lasted for four years, with
great losses in a number of flocks, and a very heavy bill for continued
expert supervision. This should be a wholesome lesson to the American
legislators who consider the prompt extinction of infection, by
abolishing this source of its increase in the living body, as a wasteful
outlay.
_Preventive Inoculation, Ovination._ If it were possible to give
immunity against sheeppox by inoculation with the exudate of cowpox, and
without danger to the sheep from fatal cowpox, or from its
transformation into the more destructive sheeppox, it would be a most
desirable resource. But experiment goes to show that vaccination is
useless, in the temperate climates at least. Sacco, Hussan, Buniva and
others in Italy vaccinated sheep extensively and claimed to have
obtained good results, but this has not been endorsed by subsequent
observers. D’Arboval vaccinated 1,523 sheep, of which 1,341 contracted
cowpox, and out of 429 of these exposed to sheeppox later, 308
contracted the latter disease. Ceely vaccinated two sheep, both of which
afterward had mild sheeppox through inoculation. Simonds and Marson
vaccinated 306 sheep, 112 of them successfully, and of these last
two-thirds contracted cowpox a second time on re-vaccination.
Twenty-nine of the successfully vaccinated sheep were inoculated with
sheeppox lymph, and in every case successfully. It is obvious that
vaccination, as a protective measure, is absolutely untrustworthy in
France or in England. Under the warm skies of Italy, as in Persia, there
may be a close relationship between the two diseases, yet in Italy
sheeppox was constantly prevalent, and it is to be feared that the
immunity in a number of cases was due to a previous attack of that
disease rather than to the vaccination. It should be noted that in
Persia sheeppox is said to be communicable to man, while in England,
Ceely failed to transmit it.
Ceely suggested variolisation with human smallpox as a preventive of
sheeppox, but Simonds and Marson failed to convey smallpox to the sheep,
though the same animal readily contracted sheeppox. One can hardly
contemplate Ceely’s proposal with equanimity. Immunity for sheep would
be dearly bought at the cost of a general diffusion of smallpox virus.
_Ovination_ or inoculation with the lymph of sheeppox is the only
available method of immunization. It entails, however, an
extraordinary multiplication of the virus in each inoculated animal,
and considering the numerous loopholes for its possible diffusion it
can only be looked on as a very dangerous and usually, in the long
run, a very expensive resort. The experience of England, above
referred to, is eloquent in witnessing against ovination, and “in
Prussia and Austria the dissemination of sheeppox went hand in hand
with inoculation.”—Friedberger and Fröhner.
On the other hand _ovination_ is not fatal to the flock operated on. The
mortality is often below 1 percent., and virtually never exceeds 4, with
a general average of about 2 per cent. It is this comparative impunity
of the inoculated flock which closes the eyes of most persons to the
great danger to a whole country and the wasteful prodigality of the
operation.
_Ovination_ further shortens the duration of the outbreak in a large
flock, passing all through the disease in 21 days, whereas as contracted
by simple exposure, the duration of the outbreak may last 90 days or
more. It further enables the owner to give such protection, shelter and
care as will guard the flock against exposure and dangerous
complications. But while preferable to the abandoning of the disease to
its natural course, it is always to be strongly condemned, where it is
possible to adopt the method which detects the sick animal in the
incipient stage by thermometry, and does away with the infection by its
removal, followed by disinfection. The only excuse for ovination is the
general prevalence of sheeppox on an island or other secluded district
where there is no great added danger from the further diffusion of the
virus, and when its simultaneous practice over the whole region can be
made the basis for universal disinfection and the definite extinction of
the contagium.
_Technique of Ovination._ The lymph (“ovine”) should be taken from a
mild case of the disease, and from a vesicle at full maturity (about the
6th day), but containing as yet a clear, translucent exudate, without
turbidity or other indication of formation of pus, or other infection.
Inoculation is made by preference on the bare lower surface of the tail
near its tip or 3 to 4 inches behind the anus. If this is unsuitable,
the inner side of the ear, an inch from the tip is usually selected,
though there is here an added element of danger, owing to its proximity
to the eye. The insertion is made with an ordinary suture needle, which
is introduced obliquely under the epidermis about one line, and pressed
upon with the thumb as it is withdrawn. A still better instrument is the
inoculation needle or lancet with a groove or spoonlike hollow on one
side. Or the skin may be scratched or abraded with the lancet, as in
vaccination, until serum oozes, when the virus is rubbed on and the part
is covered with a piece of sticking plaster. On the third or fifth day
the flock is again examined and those that have failed to _take_ are
ovinated anew.
The virus is most conveniently taken direct from the affected sheep, but
it may be preserved in capillary tubes, or on glass or ivory points, or
mixed with glycerine between glass plates, or finally, the first scab
well dried may be preserved and utilized, a minute portion being
inserted with the lancet in a pocket made under the epidermis.
Attempts have been made to secure a mitigated and safer virus, by
diluting the lymph with water or normal salt solution (1:50–150)
(Peuch), by amputating the seat of inoculation (the tip of the ear) on
the 4th or 7th day, when the vesicle is formed (Galtier), by taking a
susceptible sheep and inoculating it with sheeppox virus for ten
consecutive days, and then selecting for use the lymph from the papule
of the sixth inoculation. The inoculations of the seventh day and later
give rise to no papule even (Pourquier). By this means it is claimed
that the inoculated disease remains strictly local, passes through its
successive stages in a shorter time (15 days or less), and is perfectly
harmless to the sheep inoculated. Nocard and Mollereau sought the same
end by mixing the virus with oxygenated water, and Semmer and Raupach by
heating it to 130° F. In view of the facts that it is only under
extraordinary conditions that ovination is permissible at all, and that
the mortality, resulting from it can be kept down to about 1 per cent.,
it seems hardly worth while to attempt to obviate this loss, by any
method which may come short of the full measure of immunity.
Ovination confers immunity for a year or longer.
The care of the flock during eruption is the same as in sheeppox
contracted in the usual way.