Transactions of RHASS Volume 1940 - Page 049
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| Year | 1940 |
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’1 13M 86 SCRAPIE. be transmitted through the medium of the pasture. Accord- ingly in November 1932 the writer arranged to form at Moredun Institute a double-fenced enclosure, approximately one-half acre in extent, in which all cases of scrapie admitted to the Institute were confined. On the 11th November there were purchased twenty Half-Bred gimmers and six pregnant Cheviot ewes from farms situated in districts of Scotland in which scrapie had not been known to occur. These sheep were placed in a field immediately adjoining the scrapie enclosure, and thereafter approximately twice each week they were brought into the enclosure, while the scrapie sheep were turned out into the field occupied by the contact animals, care being taken that during the process of interchange the two lots of sheep did not come into immediate contact with each other. The ewes were served in November 1933 by :1 Cheviot ram lamb (born at Moredmi on the 18th April 1933?. the progeny of one of the Cheviot ewes, and they were again served by this ram in November 1934. There was, incidentally. a heavy death-rate in the lambs of both these lambings. Throughout the course of the experiment a few—usually three or four—cases of scrapie were maintained on the experi» mental pasture. At the conclusion of the period of experiment and observa- tion at Moredun (16th November 1935) no case of scrapie had been obServed among the contact sheep, and these were then transferred for further observation to a farm in Mid- lothian (Farm M.) on which scrapie had not been known to occur. The flock then comprised sixteen ewes (twelve Half-Breds and four Cheviots) and nine ewe hoggs—twenty-five in all; eight Half-Bred ewes and two Cheviot ewes having died during the course of the experiment from causes unconnected with scrapie, while the wet-her lambs had been disposed of. Soon after arrival at Farm M. three hoggs died in a condi— tion of debility, the precise cause of which remained undetei- mined, but no case of scrapie was observed in any of the contact sheep until February 1936, a period of approximater three years and three months after the commencement of the experiment. Between February 1936 and May 1938, when the experiment was concluded, nine other contact ewes, representing both the Half-Bred and the Cheviot flocks, developed scrapie. In three of the ten cases the diagnosis was not precisely determined, but the remaining seven were typical cases of the disease, and it was concluded that the investigation afforded very strong experimental evidence indicating that scrapie was an infective disease, the causal agent of which could be transmitted through the medium of pasture. It was at one time believed by flockmasters that mediate SCRAPIE. 87 (xi-utagion through the pasture did not occur, since in practice it had been found that the disease could be eliminated from a farm in selling off the whole flock and shortly thereafter replacmg 11 with healthy stock. The period during which pastures remain infective is, however, unknown; it may be of short ., nation. It is also true that in a considerable number of jiixlances the procedure of complete restocking has failed to eradicate the disease in so far that although it has resulted is. a marked reduction in the incidence of scrapie the disease has in due course reappeared and progressively increased in incidence. This is especially so in the caSe of lowlandfarms m which the pasture is relatively intensively grazed as distinct mum sparsely stocked hill farms on which the chance of con— iuncting infection from the pasture would be much reduced. ' (8) Transmission by Artificial I noculatwn.—'Several investi- eatOI'S have endeavoured to transmit the dlsease to expen- mental sheep by the inoculation of various material derived 1mm affected animals. - Dammann inoculated blood and nasal discharge, Besn01t med as his inocula blood and cerebral and medullary sub- ~-:1nce, while M‘Fadyean inoculated intravenously'and sub- wtaneously fourteen sheep with blood, cerebro-Spmal fluid, I-reparations of skin, and also material derived from the {:Hantois and from the foetal cotyledons. In his cases the .mimals were kept under observation for periods varying troll} approximately two years to two years six months after inoculation. In all these experiments the results were negative. Another series of experiments in which preparations of the male sexual organs were used as inocula was carried out at Alorcdim Institute under the direction of Mr W. A. Pool. The following organs—testis, epididymis, vas-deferens, accessory sex glands and urethra—from a ram which had died in an advanced stage of the disease were obtained withm a Mr hours after the animal’s death. A portion of each organ was prepared as a heavy suspension in normal saline solution, and 5 cc of each preparation was introduced directly into the pregnant uterus of six ewes by H10 flank operation. A similar volume of the suspension was injected into the News per vaginam in eight pregnant ewes. Three of these ewes received accessory sex glands, two received testis, and I '10 three others were injected with a preparation of epididymis, .us—deferens, and urethra respectively. The sheep and their progeny were kept under observation my four years nine months, and in no case were symptoms of scrapie observed. As distinct from the foregoing experiments those of Guillé and Chelle (1936) have furnished evidence that scrapie can inc artificially transmitted by inoculation. These workers, |
| Title | Transactions of RHASS Volume 1940 - Page 049 |
