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Updated: Mar 24, 2026
Clinical Examination Protocol to Detect Atypical and Classical Scrapie in Sheep
Published on: January 19, 2014
Comparison of Two US Sheep Scrapie Isolates Supports Identification as Separate Strains
S J Moore1, J D Smith1, M H West Greenlee2
1Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, US Department of Agriculture, Ames, IA.
Two distinct scrapie strains, No. 13-7 and x124, were identified in US sheep. These strains exhibit different incubation periods, prion protein (PRNP) genotype susceptibilities, and PrPSc deposition patterns, impacting disease control strategies.
Area of Science:
- Veterinary Neurology
- Infectious Diseases
- Molecular Biology
Background:
- Scrapie, a transmissible spongiform encephalopathy, affects sheep and goats globally.
- Distinct scrapie strains possess unique characteristics, but their presence and impact in the US remain largely uncharacterized.
- Prion protein (PRNP) genotype and scrapie strain influence disease susceptibility, transmission, and incubation periods (IP).
Purpose of the Study:
- To characterize two US scrapie isolates (No. 13-7 and x124) in sheep with susceptible PRNP genotypes (QQ171).
- To compare clinical signs, IPs, spongiform lesions, and PrPSc deposition patterns between the two isolates.
- To assess the influence of PRNP genotype and isolate on scrapie pathogenesis and transmission.
Main Methods:
- Intranasal inoculation of sheep with QQ171 PRNP genotype using scrapie isolates No. 13-7 and x124.
- Monitoring of clinical signs and recording of incubation periods (IPs).
- Histopathological examination for spongiform lesions and analysis of PrPSc deposition patterns in brain tissues.
- Transmission studies in C57BL/6 mice to determine attack rates.
Main Results:
- Isolate x124 showed genotype-dependent susceptibility and shorter IPs (VV136: 6.9 months, AV136: 11.9 months), with AA136 sheep remaining resistant.
- Isolate No. 13-7 caused scrapie in all inoculated sheep with longer IPs (AA136: 20.1 months, AV136: 22.8 months, VV136: 26.7 months).
- PrPSc deposition patterns varied significantly between isolates and were most distinct in VV136 sheep.
- Mouse inoculation revealed differential attack rates: 90.5% for x124 and 5.9% for No. 13-7.
Conclusions:
- No. 13-7 and x124 represent distinct scrapie strains with differing pathogenic properties.
- Host PRNP genotype significantly modulates susceptibility and incubation period depending on the specific scrapie strain.
- These findings are crucial for understanding scrapie epidemiology and developing effective control strategies in the US.
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