Assessment of the genetic risk and impact of lateral transmission in a valine-associated scrapie outbreak in sheep

Jessica M. Evoniuk Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105-5727.

Search for other papers by Jessica M. Evoniuk in
Current site
Google Scholar
PubMed
Close
 BS
,
Charles L. Stoltenow Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105-5727.

Search for other papers by Charles L. Stoltenow in
Current site
Google Scholar
PubMed
Close
 DVM
,
Katherine I. O'Rourke USDA Agricultural Research Service, Animal Disease Research Unit, 3003 ADBF, Pullman, WA 99164-6630.

Search for other papers by Katherine I. O'Rourke in
Current site
Google Scholar
PubMed
Close
 PhD
,
Bert L. Moore Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105-5727.

Search for other papers by Bert L. Moore in
Current site
Google Scholar
PubMed
Close
 PhD
, and
Dale A. Redmer Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105-5727.

Search for other papers by Dale A. Redmer in
Current site
Google Scholar
PubMed
Close
 PhD

Abstract

Objective—To characterize an outbreak of valineassociated 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.

Animals—1,006 sheep.

Procedure—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 and Clinical Relevance—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. (Am J Vet Res 2005;66:1302–1307)

Abstract

Objective—To characterize an outbreak of valineassociated 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.

Animals—1,006 sheep.

Procedure—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 and Clinical Relevance—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. (Am J Vet Res 2005;66:1302–1307)

Advertisement