Genetic susceptibility and transmission factors in scrapie: detailed analysis of an epidemic in a closed flock of Romanov

Information from a scrapie epidemic in a closed INRA Romanov flock is presented. Performances, pedigree, histopathological diagnoses and PrP genotypes were recorded from the beginning of the outbreak (in 1993). Between I st of April, 1993 and I st of May, 1997, 1015 animals were exposed to scrapie, and 304 died from this disease. A major influence of the polymorphisms at codons 136, 154 and 171 is shown, A(136)H(153)Q(171) allele carriers proving to be nearly as resistant as A(136)R(154)R(171) carriers. A possible relationship between gastrointestinal parasitism and scrapie is discussed. There is evidence of maternal transmission, with a risk; ratio for artificially fed lambs of 67 percent of the risk of lambs fed by their mother. Our results strongly suggest that resistant animals were not healthy carriers or at least were less infectious when comparing risk for lambs born to healthy dams either of resistant (risk = 0.431) or of susceptible (risk = 1.000) genotype.