Transactions of RHASS Volume 1940 - Page 050
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| Year | 1940 |
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88 SCRAPIE. using inocula derived from the cerebrum, medulla, and spinal cord of several sheep in the later stages of scrapie, inoculated seventeen healthy sheep by the intra-cerebral, epidural, intra—ocular, subcutaneous, and intra—cutaneous routes. 01‘ these seventeen experimental sheep nine died from inter- current affections, but of the remaining eight animals tVVU which received a preparation of spinal cord by intra-ocular inoculation developed symptoms of scrapie fourteen and a half and twenty-two months after inoculation; one sheep which received an emulsion of medulla epidurally and one which received this inoculum subcutaneously developed scrapie after intervals of one year and of nineteen and a half months respectively; one other sheep which received an intra-cerebral inoculation of spinal cord developed scrapie eleven months after inoculation, while the three remaining experimental sheep continued in apparent health. It would thus appear that out of seventeen experimental animals the positive transmission of scrapie had been effected in five cases. In a further series of experiments two healthy lambs each received, partly by intra-ocular and partly by subcutaneous injection, a filtered emulsion (Chamberland L. 3) of scrapie spinal cord. Both these lambs developed typical symptoms of scrapie sixteen months later. It would appear, therefore, that the work of Cuillé and Chelle furnishes further experimental evidence that scrapie is an infective disease and that it can be transmitted artificially by inoculation. It also indicates (although confirmation of this is yet lacking) that the causal agent of the disease is capable of passing a comparatively fine porcelain filter, and that it therefore probably represents a filtrable virus. Bertrand, Carré, and Lucam, with the object of testing the results obtained by Cuillé and Chelle, inoculated twelve sheep—nine by intra-cerebral injection, two subcutaneously. and one by skin scarification—with suspension preparations of the brain and spinal cord obtained from sheep showin: typical symptoms of scrapie. The results were uniformly negative, but with the exception of one ewe—inoculatel intra-cerebrally—Which was kept under observation for twenty—three months, none of the other experimental anima‘s was observed for a period longer than three and a half months. Recent observations by the Animal Diseases Research Association indicate that a very considerable number of sheep inoculated with virulent scrapie material remain refrac- tory to the development of the disease, and in consideration of the very small numbers of experimental sheep employed by Bertrand, Carré and Lucam, and the quite inadequaie periods during which they were kept under observation, it is considered that these experiments should properly be regarded as being without significance". SCRAPIE. 89 In 1937 the Animal DiScases Research Association, as the result of field observations involving several thousand sheep, 1,wcame possessed of evidence indicating (a) that the infective scent of scrapie is present in the brain, Spinal cord, and/or :ilif‘fi‘n, (b) that it can withstand a concentration of formalin ti” at least 0'35 per cent, (0) that it can be transmitted by subcutaneous inoculation, and (d) that the incubative period ii" the infection may extend to at least two years. In view of this knowledge the Association in 1938 purchased I healthy—that is, a non-scrapie—hirsel comprising over live hundred sheep, and these are being maintained as an experimental flock for the purpose of carrying out a systematic study of the disease and of determining the nature of the musal agent. Because of the prolonged incubative period .il’ scrapie it follows that the investigations must necessarily HWOI‘ a period of several years ; the results will be published in due course. In preparing this paper the writer has endeavoured to collate and to preSent in somewhat concise form such knowledge 01' scrapie as is now available. It would appear that scrapie represents a neurosis charac- h-rised by symptoms of intense and progressive pruritus or Eich, progressive debility, and locomotor inco—ordination. The . nurse, which may extend over several months, almost invari- ably terminates fat-ally. There is now evidence that the disease is due to a living infective agent the nature of which is not yet precisely deter- mined. The incubative period of the disease is prolonged and is frequently of two years’ duration. The evidence indicates that under natural conditions the .lisease may be transmitted by means of congenital infection and through the medium of infected pasture. It may also be transmitted by artificial inoculation. There is now evidence such as to permit the belief that many sheep which become infected with scrapie do not show any obvious sign of the disease ; such sheep if used for breeding may, nevertheless, transmit the infection to their progeny, in which it may or may not become manifest. This remarkable feature of scrapie—120., the propensity of the disease to remain latent, yet still infective, through one or more generations, “(11(1 also the fact that in any individual animal a prolonged period elapses between actual infection and disease inani- lestation, have been among the chief reasons why our study of scrapie has so long been beset with conflicting evidence, Ihe meaning of which was so often obscure. The investigation upon which the Animal Diseases Research Association is now engaged has as its ultimate objects the VOL. LII. G |
| Title | Transactions of RHASS Volume 1940 - Page 050 |
