Transactions of RHASS Volume 1940 - Page 046
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| Year | 1940 |
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80 SCRAPIE. reached the conclusion that the histological changes repre- sented a sub-acute polio-myel-encephalitis (inflammation of the grey matter of the brain and spinal cord). For several years the histological changes which occur in scrapie have been systematically studied at Moredun Institute by Brownlee, and the results of the investigation, which form the subject of a separate paper, will shortly be published. PHYSIOLOmoo-BIOCHEMICAL STUDIES. A study of the biochemistry of scrapie indicated that an acute disturbance of the carbohydrate metabolism was frequently associated with the disease; it was therefore arranged to carry out a systematic study of the basal metabolic rate which obtains in scrapie. The work, which extended over one year, was undertaken at Moredun Institute by Professor H. Dryerre and Professor J. Yule Bogue ; it showed that the metabolic rate remained relatively unaffected through- out the course of the disease. POSSIBLE METHODS OF TRANSMISSION. (1) Hereditary Transmission.—The term “ scrapie ram” is used in reference to a rain which develops scrapie subsequent to his being used at stud in a clean flock, and also to one which has been bred in a flock in which the disease is present. It has been commonly observed that such rams may never show signs of the disease. or prolonged periods—in some cases several years—may elapse between the occurrence of Symptoms of scrapie in the progeny and the subsequent manifestation of the disease in the ram. It is also recognised that scrapie frequently appears in the progeny of ewes which later showed evidence of the disease, although upon occasion it may also attack lambs, the mothers of which remained apparently free from and had no known connection with scrapie. These facts, which have been long established, prompted the question whether scrapie arose not from a living infective agent, but from a diathesis or special liability to the diseasc which could be transmitted from the immediate. or even the more remote, parents to the progeny. This hypothesis seemed to be supported by a variety of evidence, including the apparent inability of a scrapie ram to transmit the disease venereally to his ewes, the consistent failure to demonstrate the presence of pathogenic micro-organisms, and also the repeated failure of several investigators to set up the disease experimentally by artificial inoculation of material derived from affected sheep. On the other hand, the present writer and others SCRAPIE. 81 have observed that in the case of a flock which had recently become infected as the result of the introduction of a scrapie .‘21-111 the disease in the course of time tended to spread and eventually became manifest among members of the flock which had no relationship to the ram concerned. Such observations, ‘hereforc, suggested that the cause of the disease was a *iving infective agent. . ' _ It has been already indicated that scrapie is relatively arevalent in certain breeds, and that others, notably the Scottish Blackfaces, are seldom affected with the_natura1 disease. It may therefore be accepted, but only'w1th_con- siderable reserve, that some degree of breed diathes1s to scrapie may exist. 011 the other hand, a close study of the oreeding strains in a large pedigree flock which for several years had been affected with scrapie afforded no evidence lhat any particular strain was specially susceptible ;- indeed, the disease in this instance appeared quite erratically in different unrelated strains. (2) Vcncreal Infection.—It has been frequently stated that scrapie can be transmitted venereally from the ram to the :‘W6. Stockman formed the conclusion that the disease was directly and/0r indirectly contagious, and he believed it possible that scrapie might be transmitted to the ewe or ram hv the sexual act. ' _ [In every case, however, of alleged venereal transnnssmn which the writer has investigated, the evidence was such that it is permissible to doubt whether such supposed cases could not be explained on other grounds. _ _ The following obServations may be cited as indicative that the disease is not transmitted venereally, and numerous similar instances could be quoted. . (a) A shearling Half-Bred ram, soon after his introduction to a ‘clean’ flock, was mated with fifty ewes, and during the subSequent breeding season he served approximately the same number, but immediately after his second period at stud he developed typical scrapie. In consequence the progeny of the ram were fattened and sold to the butcher, and it was found that the disease was not transmitted to the cues which he had served or to their subsequent progeny by other rams. (b) A certain Border Leicester ram served about sixty ewes which were pastured in a park by themselves. The rain developed scrapie about six or seven months after completion of stud. \Vhen the progeny of this scrapie ram became _:'immers the disease appeared in them in an incidence of about five or six per cent, but no case of scrapie occurred in the ewes. - While it would not be proper to assert that the disease is never transmitted venereally from ram to ewe, or con— |
| Title | Transactions of RHASS Volume 1940 - Page 046 |
