Search Results

Abstract

Objective—To characterize an outbreak of West Nile virus (WNV) infection in horses in North Dakota in 2002, evaluate vaccine effectiveness, and determine horse characteristics and clinical signs associated with infection.

Design—Retrospective study .

Animals—569 horses.

Procedure—Data were obtained from veterinary laboratory records, and a questionnaire was mailed to veterinarians of affected horses.

Results—Affected horses were defined as horses with typical clinical signs and seroconversion or positive results of virus isolation; affected horses were detected in 52 of the 53 counties and concentrated in the eastern and northeastern regions of the state. Among affected horses, 27% (n = 152) were vaccinated against WNV, 54% (309) were not, and 19% (108) had unknown vaccination status; 61% (345) recovered, 22% (126) died, and 17% (98) had unknown outcome. The odds of death among nonvaccinated horses were 3 and 16 times the odds among horses that received only 1 or 2 doses of vaccine and horses that were vaccinated according to manufacturer's recommendations, respectively. Horses with recumbency, caudal paresis, and age > 5 years had higher odds of death, whereas horses with incoordination had lower odds of death, compared with affected horses without these characteristics.

Conclusions and Clinical Relevance—Vaccination appears to have beneficial effects regarding infection and death caused by WNV. ( J Am Vet Med Assoc 2004;225:1084–1089)

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 determine whether selection for the homozygous A₁₃₆R₁₇₁ genotype that confers resistance to classic scrapie infection negatively affects production traits in sheep.

Animals—996 commercial lambs obtained from 2 flocks at separate locations across 3 consecutive years.

Procedures—Genotyping at codon 136 and 171 was performed by use of commercially available testing or a single-nucleotide polymorphism assay. Carcass data were collected without knowledge of genotype approximately 24 hours after slaughter by an experienced grader. The model to analyze associations between prion protein (PRNP) genotype and production traits was based on genotype, breed, or both as fixed effects and days on feed as a covariate.

Results—Average daily gain was significantly associated with only combined codons 136 and 171. In flock 1, weaning average daily gain was significantly greater in AA₁₃₆ sheep than heterozygotes; the difference between QR₁₇₁ and RR₁₇₁ sheep, compared with QQ₁₇₁ sheep, were not significant although QR₁₇₁ and RR₁₇₁ sheep had higher values. However, in flock 2, average daily gain was significantly greater in AV₁₃₆ sheep than AA₁₃₆ sheep and in QR₁₇₁ sheep than QQ₁₇₁ sheep.

Conclusions and Clinical Relevance—Findings suggest there is an advantage for average daily gain in lambs with an arginine allele at codon 171, but there were no other genotype effects on production traits. Thus, selection for the resistant arginine allele at codon 171 to comply with USDA scrapie eradication guidelines should not be detrimental to lamb production in commercial flocks. Effects of codon 136 on average daily gain were ambiguous.