Scrapie prevalence in sheep of susceptible genotype is declining in a population subject to breeding for resistance

Abstract

BackgroundSusceptibility of sheep to scrapie infection is known to be modulated by the PrP genotype of the animal. In the Netherlands an ambitious scrapie control programme was started in 1998, based on genetic selection of animals for breeding. From 2002 onwards EU regulations required intensive active scrapie surveillance as well as certain control measures in affected flocks.Here we analyze the data on genotype frequencies and scrapie prevalence in the Dutch sheep population obtained from both surveillance and affected flocks, to identify temporal trends. We also estimate the genotype-specific relative risks to become a detected scrapie case.ResultsWe find that the breeding programme has produced a steady increase in the level of genetic scrapie resistance in the Dutch sheep population. We also find that a significant decline in the prevalence of scrapie in tested animals has occurred a number of years after the start of the breeding programme. Most importantly, the estimated scrapie prevalence level per head of susceptible genotype is also declining significantly, indicating that selective breeding causes a population effect.ConclusionsThe Dutch scrapie control programme has produced a steady rise in genetic resistance levels in recent years. A recent decline in the scrapie prevalence per tested sheep of susceptible prion protein genotype indicates that selective breeding causes the desired population effect.

Single nucleotide polymorphisms at 15 codons of the prion protein gene from a scrapie-affected herd of Suffolk sheep in Brazil

“…In The Netherlands an eradication programme of susceptible animals has been enforced since 2002 with a corresponding downward trend in the prevalence of scrapie in country Hagenaars et al 2010).…”

Caprine PrP variants harboring Asp-146, His-154 and Gln-211 alleles display reduced convertibility upon interaction with pathogenic murine prion protein in scrapie infected cells

“…In sheep, recruitment of genetically resistant animals in selective breeding programs, targeting the almost absolute protective Ala-136,Arg-154,Arg-171 allele, 6 yielded very promising results and significantly reduced disease prevalence. 7,8 Even though FIGURE 3. Goat specific Proteinase K-resistant moieties produced in the 22LN2a#58 cells are different from PrP SC molecules of naturally occurring goat scrapie cases.…”

“…6 Non-synonymous Single Nucleotide Polymorphisms (SNPs) present in the ovine Prnp have been strongly associated with resistance and were targeted by selective breeding strategies, resulting in significant reduction of disease prevalence. 7,8 Unfortunately, this has not yet been applied in the case of goats, as the most promising scrapie-protective allele(s) has not been determined yet.…”

Changes in allele and genotype frequencies of PrP gene in breeds of sheep in Slovakia between 2004 and 2015

“…Results from sheep selection for resistance to classical scrapie in EU countries where sheep industry is highly developed indicate success (Hurtado et al, 2002;Hagenaars et al, 2010), despite the fact that in the beginning of implementation of the national scrapie eradication programmes there were high differences among breeds as far as the occurrence of risk genotypes is related. Unfortunately, the above mentioned classification system of five risk groups does not work when so called atypical scrapie occurs (Fast and Groschup, 2013).…”