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.