Experimental Oral Transmission of Atypical Scrapie to Sheep

Marion M Simmons,S Jo Moore,John Spiropoulos,Lisa Thurston,Leigh Thorne,Stephen A.C Hawkins,Linda A Terry,Richard Lockey,Chris Vickery,Timm Konold,Melanie J Chaplin

doi:10.3201/eid1705.101654

Abstract

To investigate the possibility of oral transmission of atypical scrapie in sheep and determine the distribution of infectivity in the animals' peripheral tissues, we challenged neonatal lambs orally with atypical scrapie; they were then killed at 12 or 24 months. Screening test results were negative for disease-specific prion protein in all but 2 recipients; they had positive results for examination of brain, but negative for peripheral tissues. Infectivity of brain, distal ileum, and spleen from all animals was assessed in mouse bioassays; positive results were obtained from tissues that had negative results on screening. These findings demonstrate that atypical scrapie can be transmitted orally and indicate that it has the potential for natural transmission and iatrogenic spread through animal feed. Detection of infectivity in tissues negative by current surveillance methods indicates that diagnostic sensitivity is suboptimal for atypical scrapie, and potentially infectious material may be able to pass into the human food chain.

Highlights

To investigate the possibility of oral transmission of atypical scrapie in sheep and determine the distribution of infectivity in the animals’ peripheral tissues, we challenged neonatal lambs orally with atypical scrapie; they were killed at 12 or 24 months
Since the discovery of atypical scrapie [1] and its subsequent identification, mostly through active surveillance, in several countries [2,3] such as New Zealand [4] and Australia [5], scientists have debated whether this form of TSE is spontaneous or acquired [3,4,6,7,8] rather than contagious
The tissue distribution of infectivity or disease-specific prion protein (PrPSc) in bovine spongiform encephalopathy in sheep has led to extensive public health control measures based on the known pathogenesis and distribution of PrPSc in edible tissues, and their removal from carcasses of animals over a certain age

Summary

Introduction

To investigate the possibility of oral transmission of atypical scrapie in sheep and determine the distribution of infectivity in the animals’ peripheral tissues, we challenged neonatal lambs orally with atypical scrapie; they were killed at 12 or 24 months. Infectivity of brain, distal ileum, and spleen from all animals was assessed in mouse bioassays; positive results were obtained from tissues that had negative results on screening These findings demonstrate that atypical scrapie can be transmitted orally and indicate that it has the potential for natural transmission and iatrogenic spread through animal feed. Early studies of atypical scrapie did not show PrPSc or infectivity outside the brain, recent data indicate that peripheral tissues from naturally infected animals can harbor infectivity either in the presence or absence of PrPSc [22] Whether this infectivity is established before or after the agent has propagated in the central nervous system is unknown

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Results