%0 Journal Article
%T Scrapie prevalence in sheep of susceptible genotype is declining in a population subject to breeding for resistance
%A Thomas J Hagenaars
%A Marielle B Melchior
%A Alex Bossers
%A Aart Davidse
%A Bas Engel
%A Fred G van Zijderveld
%J BMC Veterinary Research
%D 2010
%I BioMed Central
%R 10.1186/1746-6148-6-25
%X 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.We 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.The 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.Scrapie in sheep is a transmissible spongiform encephalopathy (TSE) present in most sheep-producing countries [1,2]. Infection with (classical) scrapie is thought to occur at young age, after which it takes an incubation period of one or more years before clinical signs, such as uncoordinated movement, abnormal postures and severe scratching, become apparent. During this incubation period the infectious prion protein PrPSc accumulates in the animal [3]. Scrapie control has become a priority in many countries mainly because experimental infection of sheep with bovine spongiform encephalopathy (BSE) has shown that sheep can be infected via the oral route and that the resulting clinical symptoms are very similar to scrapie [4]. Fears that BSE may have been introduced into sheep through consumption of feed supplements in the past, with potential consequences to public health [5,6], have eased somewhat recently since tests of millions of sheep have not p
%U http://www.biomedcentral.com/1746-6148/6/25