Immunoglobulin G concentrations in the sera of Herdwick sheep with natural scrapie

Studies have been made of a flock of Herdwick sheep, genetically selected for susceptibility to experimental infection with scrapie, in which an extensive outbreak of the natural disease has occurred. One hundred and fifteen sheep in 3 lamb crops (1974, 1975 and 1976) were bled at approximately 6 monthly intervals and measurements made of the concentration of IgG in serum. Sixty-seven of these sheep developed natural scrapie at 21 to 28 months of age. Between 41 and 88 per cent of the scrapie cases (depending on the lamb crop) had greatly increased concentrations of IgG in the clinical stage of the disease. On average, the increases were about 70 to 90 per cent above the concentrations of IgG found in normal and scrapie sheep of 2 to 18 months of age. The significance of these changes is not known but it is suggested that they may be associated with the deposition of cerebral amyloid which is known to be a feature of some experimental models of scrapie in mice.