The Effectiveness of on-Farm Decontamination Methods for Scrapie

<p>Scrapie infectivity persists on farms where infected animals have been removed1. Recently we have
demonstrated that it is possible to detect environmental scrapie contamination biochemically using serial Protein
Misfolding Cyclic Amplification (sPMCA)2, allowing the monitoring of scrapie infectivity on farm premises. Ongoing
Defra study SE1863 has compared pen decontamination regimes on a scrapie-infected farm by both sheep
bioassay and sPMCA. For bioassay, scrapie-free genetically susceptible lambs were introduced into pens
decontaminated using distinct methodologies, all pens contained scrapie-positive lambs within 1 year.
Remarkably this included lambs housed within a pen which had been jet washed/chloros treated, followed by regalvanisation/replacement of all metalwork and painting of all other surfaces.</p>
<p>We have recently demonstrated using sPMCA, that material collected on swabs from vertical surfaces at heights
inaccessible to sheep within a barn on the same scrapie affected farm contained scrapie prions (unpublished
observations). We hypothesise that scrapie prions are most likely to have been deposited in these areas by
bioaerosol movement. We propose that this bioaerosol movement contributes to scrapie transmission within the
barn, and could account for the sheep that became positive within the pen containing re-galvanised/new metalwork and repainted surfaces (project SE1863). It is proposed that a thorough decontamination that would minimise prion-contaminated dust, both within the building and its immediate vicinity, is likely to increase the effectiveness of current methods for decontaminating farm buildings following outbreaks of scrapie. The proposed study builds on our previous data and will thoroughly investigate the potential for farm building scrapie contamination via the bioaerosol route, a previously unrecognised route for dissemination of scrapie infectivity. This route could lead to the direct infection of healthy animals and/or indirect transmission of disease via contamination of surfaces within animal pens. The proposed study would analyse material collected using air samplers set up within “scrapie-infected” barns and their immediate vicinity, to confirm that prion containing material can be airborne within a scrapie infected farm environment. The study would incorporate a biochemical assessment of different surface decontamination methods, in order to demonstrate the best methodology and then the analysis of air and surface samples after a complete building decontamination to remove sources of dust and surface bound prions from both the building and its immediate vicinity. Analysis of such surface and air samples collected before and after treatment would measure the reduction in levels of infectivity. It is envisaged that the biochemical demonstration of airborne prions and the effective reduction in such prion dissemination would lead to a sheep bioassay experiment that would be conducted after a full farm decontamination. This would fully assess the effectiveness of an optimised scrapie decontamination strategy.</p>
<p>This study will contribute directly to Defra policy on best practice for on-farm decontamination after outbreaks of
scrapie; a situation particularly relevant to decontamination after scrapie cases on goat farms where no genetic
resistance to scrapie has currently been identified, and where complete decontamination is essential in order to
stop recurrence of scrapie after restocking.</p>