Atypical/Nor98 scrapie infectivity in sheep peripheral tissues

Area of Science:

• Veterinary Medicine
• Infectious Diseases
• Neuroscience

Background:

• Atypical/Nor98 scrapie is a global small ruminant disease, a significant portion of European transmissible spongiform encephalopathies (TSEs).
• It affects sheep genetically resistant to other TSEs, with poorly understood pathogenesis.
• Previously, low human and animal exposure risk was assumed due to undetectable abnormal prion protein (PrP) in peripheral tissues.

Purpose of the Study:

• To investigate the presence of Atypical/Nor98 scrapie infectivity in peripheral tissues.
• To evaluate the impact of PrP detection methods on disease surveillance.
• To reassess the potential dietary exposure risk associated with Atypical/Nor98 scrapie.

Main Methods:

• Analysis of lymphoid tissues, nerves, and muscles from natural and experimental Atypical/Nor98 scrapie cases.
• Comparison of infectivity detection with abnormal prion protein (PrPSc) presence.
• Estimation of infectivity loads in peripheral tissues of Atypical/Nor98 and classical scrapie cases.

Main Results:

• Infectivity was found in lymphoid tissues, nerves, and muscles, irrespective of detectable abnormal PrP.
• Atypical/Nor98 scrapie samples can be PrP(Sc) negative, challenging current detection methods.
• Peripheral tissues showed varying infectivity loads in both Atypical/Nor98 and classical scrapie cases.

Conclusions:

• Atypical/Nor98 scrapie infectivity can accumulate in peripheral tissues without PrP(Sc) detection, impacting disease surveillance.
• Current risk assessments for Atypical/Nor98 scrapie may underestimate transmissibility and prevalence.
• Dietary exposure risk from small ruminant TSEs might be higher than previously believed.