title: Assessment of the genetic risk and impact of lateral transmission in a valine-associated scrapie outbreak in sheep.
abstract: OBJECTIVE
  To characterize an outbreak of valine-associated scrapie, assess the relative risk of scrapie infection in relation to allele frequency at codon 136, and investigate lateral transmission of infection in a sheep flock within the United States.
  
  
  METHODS
  1,006 sheep.
  
  
  METHODS
  To determine genotypes, blood or semen samples were assessed via commercial testing; in 190 slaughtered sheep, scrapie status was determined via immunohistochemical evaluation of tissues. Scrapie-positive sheep born to scrapie-negative dams and sheep infected after 1 year of age were identified to assess lateral transmission.
  
  
  RESULTS
  Genotypes were determined for codon 171 (164 sheep) or codons 136 and 171 (842 sheep). Forty-four of 160 slaughtered sheep of known genotype were scrapie positive. In these sheep, the presence of at least 1 valine allele at codon 136 (V136) was highly correlated with scrapie-positive status. Lateral transmission was the probable source of infection for 4 scrapie-positive sheep born to scrapie-negative dams and for 11 sheep in which scrapie was diagnosed at > 50 months of age.
  
  
  CONCLUSIONS
  Results suggest that the outbreak of scrapie was associated with a relatively high frequency of V136 in the flock, introduction of a valine-dependent scrapie strain, and the occurrence of lateral transmission. Genotyping of sheep may assist management decisions following diagnosis of scrapie in a sheep with at least 1 V136. It may be prudent to remove sheep of the diploid genotype AVQR (at codons 136 and 171) from infected flocks.
authors.affiliation: Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105-5727, USA.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Evoniuk
authors.forename: Charles L
authors.initials: CL
authors.lastname: Stoltenow
authors.forename: Katherine I
authors.initials: KI
authors.lastname: O'Rourke
authors.forename: Bert L
authors.initials: BL
authors.lastname: Moore
authors.forename: Dale A
authors.initials: DA
authors.lastname: Redmer
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D004196:Disease Outbreaks / Q000662:veterinary*; D018562:Disease Transmission, Infectious / Q000662:veterinary*; D005260:Female; D020022:Genetic Predisposition to Disease; D005838:Genotype; D008297:Male; D011328:Prions / Q000235:genetics; D012608:Scrapie / Q000235:genetics* / Q000635:transmission*; D012756:Sheep; D014633:Valine / Q000235:genetics
chemical_list: D011328:Prions; D014633:Valine