Multiple sclerosis and scrapie.

Field, Miller, and Russell (1962) reported that sheep in Iceland injected intracerebrally by Dr. Palsson with a suspension of the brain of an acute case (SELL) of multiple sclerosis developed a disease histologically indistinguishable from scrapie. In the following year, Campbell, Norman, and Sandry (1963) noted that Dr. Palsson had again elicited a scrapie-like disease in sheep injected intracerebrally with a suspension of pathological human brain material. On this occasion the inoculum was a suspension of brain and spinal cord from a fatal case of subacute encephalitis of unknown aetiology. Histological examination of the central nervous system of two of the four inoculated sheep showed changes which have been regarded as characteristic of scrapie by Zlotnik and Stamp (1962), but the ponto-cerebellar and other abnormalities observed in scrapie sheep in England by Beck, Daniel, and Parry (1964) were not seen. In 1964 Palsson, Pattison, and Field (unpublished data) reported that all of the original sheep, fourin number, inoculated with SELL brain in Iceland developed neurological illnesses and showed histological signs of scrapie. Furthermore they recorded that the experiment had been repeated in Iceland in that two of five sheep inoculated with the same brain material developed signs of scrapie, and that sheep-to-sheep passage experiments had been successfully done. The clinical pictures of multiple sclerosis and scrapie are very different as are also the lesions in the central nervous system. Indeed the only common features in the two conditions are involvement of the central nervous system and long incubation periods (if indeed multiple sclerosis is due to an infective agent). It seems most unlikely that the same agent could be responsible for such dissimilar diseases unless as the precipitating factor of two different conditions. There have, however, been suggestions that sheep might play some part in the natural history of multiple sclerosis (Campbell, Daniel, Porter, Russell, Smith, and Innes, 1947; Sutherland and Wilson, 1951; Campbell, 1963) and in view of the findings in sheep reported by Field et al. (1962) and Palsson et al. (unpublished data) we decided to try to repeat their experiment. In addition to testing the brain material (SELL) which initiated scrapie in sheep in Iceland we also inoculated sheep with material from the central nervous system from six other fatal cases of multiple sclerosis. At the same time we inoculated monkeys intracerebrally with aliquots of the central nervous system suspension which we tested in sheep. Finally we inoculated monkeys with suspensions of scrapieinfected brain from sheep, goats, and mice in an attempt to reproduce the disease in these animals.