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

Abstract

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 1st of April, 1993 and 1st 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, A136H154Q171 allele carriers proving to be nearly as resistant as A136R154R171 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.

Using genotype probabilities in survival analysis: a scrapie case

“…Data were obtained from an INRA experimental flock ("Langlade") located near Toulouse (France) and first described by Elsen et al [6]. The present study includes data from animals of the Romanov breed.…”

“…The present study includes data from animals of the Romanov breed. In August 1993, the flock suffered an outbreak of scrapie and the natural selection against the susceptible genotypes drastically changed the distribution of the different genotypes [6]. Since then, appropriate matings of PrP-genotyped animals (i.e.…”

“…Survival analysis provides an adequate framework to analyze resistancesusceptibility to scrapie [1,6]. Survival analysis has been used to analyze scrapie genetic resistance in the INRA Langlade flock [3,6].…”

“…Survival analysis has been used to analyze scrapie genetic resistance in the INRA Langlade flock [3,6]. These two studies handled missing genotypes differently.…”

“…These two studies handled missing genotypes differently. While Elsen et al [6] discarded information of non-genotyped individuals, Díaz et al [3] included this information in the analyses. Díaz et al [3] compared two different approaches to account for the unknown information on the PrP genotype in order to estimate the risk associated with it.…”