title: The evaluation of exposure risks for natural transmission of scrapie within an infected flock.
abstract: BACKGROUND
  Although the epidemiology of scrapie has been broadly understood for many years, attempts to introduce voluntary or compulsory controls to eradicate the disease have frequently failed. Lack of precision in defining the risk factors on farm has been one of the challenges to designing control strategies. This study attempted to define which parts of the annual flock management cycle represented the greatest risk of infection to naive lambs exposed to the farm environment at different times.
  
  
  RESULTS
  In VRQ/VRQ lambs exposed to infected sheep at pasture or during lambing, and exposed to the buildings in which lambing took place, the attack rate was high and survival times were short. Where exposure was to pasture alone the number of sheep affected in each experimental group was reduced, and survival times were longer and related to length of exposure.
  
  
  CONCLUSIONS
  At the flock level, eradication and control strategies for scrapie must take into account the need to decontaminate buildings used for lambing, and to reduce (or prevent) the exposure of lambs to infected sheep, especially in the later stages of incubation, and at lambing. The potential for environmental contamination from pasture should also be considered. Genotype selection may still prove to be the only viable tool to prevent infection from contaminated pasture, reduce environmental contamination and limit direct transmission from sheep to sheep.
authors.affiliation: Veterinary Laboratories Agency, Woodham Lane, New Haw, Addlestone, Surrey KT15 3NB, UK. g.dexter@vla.defra.gsi.gov.uk
authors.forename: Glenda
authors.initials: G
authors.lastname: Dexter
authors.forename: Sue C
authors.initials: SC
authors.lastname: Tongue
authors.forename: Lindsay
authors.initials: L
authors.lastname: Heasman
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Bellworthy
authors.forename: Andrew
authors.initials: A
authors.lastname: Davis
authors.forename: S Jo
authors.initials: SJ
authors.lastname: Moore
authors.forename: Marion M
authors.initials: MM
authors.lastname: Simmons
authors.forename: A Robin
authors.initials: AR
authors.lastname: Sayers
authors.forename: Hugh A
authors.initials: HA
authors.lastname: Simmons
authors.forename: Danny
authors.initials: D
authors.lastname: Matthews
mesh_terms: D000818:Animals; D004781:Environmental Exposure; D005260:Female; D011247:Pregnancy; D016016:Proportional Hazards Models; D012307:Risk Factors; D012608:Scrapie / Q000401:mortality / Q000473:pathology / Q000635:transmission*; D012756:Sheep; D016019:Survival Analysis; D013997:Time Factors