Classical sheep scrapie in Great Britain: spatial analysis and identification of environmental and farm-related risk factors
Kim B Stevens , Victor J Del Rio Vilas and Javier Guitian
BMC Veterinary Research 2009, 5:33doi:10.1186/1746-6148-5-33
Published: 8 September 2009
Background Previous studies suggest that the spatial distribution of classical sheep scrapie in Great Britain is uneven and that certain flock characteristics may be associated with occurrence of the disease. However, the existence of areas of high and low disease-risk may also result from differences in the spatial distribution of environmental characteristics. In this study we explored the spatial pattern of classical scrapie in Great Britain between 2002 and 2005 and investigated the association between disease occurrence and various environmental and farm-related risk factors.
Results Exploratory spatial analysis: South Wales was found to have a higher densisty of scrapie-positive farms than the rest of Great Britain. In addition, a small cluster of high-risk farms was identified in the center of this region in which clustering of scrapie-positive farms occurred up to a distance of approximately 40 km. Spatial modelling: A mixed-effects regression model identified flock-size and soil drainage to be significantly associated with the occurrence of scrapie in England and Wales (area under the curve (AUC) 0.71 +/- 0.01, 95% CI 0.68 - 0.74). The predictive risk map based on the estimated association between these factors and disease occurrence showed most of Wales to be at risk of being confirmed positive for scrapie with areas of highest risk in central and south Wales. In England, areas with the highest risk occurred mainly in the north and the midlands.
Conclusions The observed distribution of scrapie in Great Britain exhibited a definite spatial pattern with south Wales identified as an area of high occurrence. In addition both flock (flock size) and environmental variables (soil drainage) were found to be significantly associated with the occurrence of the disease. However, the model's AUC indicated unexplained variation remaining in the model and the source of this variation may lie in farm-level characteristics rather than spatially-varying ones such as environmental factors.
PRIONS ADHERE TO SOIL AND REMAIN INFECTIOUS
J.M. Aiken1, C. Johnson1,2, X.Ma, D.McKenzie1, J.P. Pedersen3 1Department of Animal Health and Biomedical Sciences, 2Program in Cellular and Molecular Biology, 3Department of Soil Science, University of Wisconsin, Madison, WI, USA firstname.lastname@example.org
An unidentified environmental reservoir of infectivity contributes to the natural transmission of prion diseases (transmissible spongiform encephalopathies, TSEs) in sheep, deer and elk. Prion infectivity may enter soil environments via shedding from diseased animals and decomposition of infected carcasses. We examined the potential for soil to serve as a TSE reservoir by studying the sorption of the disease-associated prion protein (PrPSc) with common soil minerals. We demonstrated substantial PrPSc adsorption to whole soils as well as clay minerals (montmorillonite and kaolinite) and quartz. We quantified the PrPSc binding capacities of each mineral examined. Furthermore, the PrPSc desorbed from montmorillonite (Mte) clay was cleaved at an N-terminal site and the interaction between PrPP Sc and Mte was strong, making desorption of the protein difficult. Despite cleavage and avid binding, PrPSc bound to Mte remained infectious. Results from our study suggest that PrPSc released into soil environments is maintained in a bioavailable form, perpetuating prion disease epizootics and exposing other species to infectious agent.
Saturday, January 24, 2009
Research Project: Detection of TSE Agents in Livestock, Wildlife, Agricultural Products, and the Environment Location: 2008 Annual Report