NATURAL SCRAPIE IN A CLOSED FLOCK OF CHEVIOT SHEEP OCCURS ONLY IN SPECIFIC PRP GENOTYPES

Natural scrapie in a closed flock of South Country Cheviot sheep has r esulted in 45 deaths between 1986 and 1995. Of these cases, 35 sheep h ave been analysed for disease-linked PrP gene polymorphisms and all en code valine at codon 136 on at least one allele with 77% homozygous (V V136) and 23% valine/alanine heterozygotes (VA(136)). Mean survival ti me was 907 and 1482 days for VV136 and VA(136) scrapie affected animal s respectively. VV136 animals were all at great risk of disease if all owed to live long enough. However scrapie occurred only in a specific subgroup of VA(136) sheep, survival advantage depending on VA(136) ani mals being heterozygous for other polymorphisms at coons 154 or 171. T he flock history has been recorded in great detail since its foundatio n in 1960 however there was no strong evidence for simple maternal or paternal transmission of disease other than inheritance of PrP genotyp e.