Email updates

Keep up to date with the latest news and content from BMC Veterinary Research and BioMed Central.

Open Access Highly Accessed Research article

Evidence of effective scrapie transmission via colostrum and milk in sheep

Timm Konold1*, S Jo Moore23, Susan J Bellworthy2, Linda A Terry2, Leigh Thorne4, Andrew Ramsay4, F Javier Salguero1, Marion M Simmons1 and Hugh A Simmons1

Author Affiliations

1 Specialist Scientific Support Department, Animal Health and Veterinary Laboratories Agency Weybridge, New Haw Addlestone, Surrey KT15 3NB, UK

2 Formerly – Veterinary Laboratories Agency Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK

3 School of Veterinary and Biomedical Sciences, Murdoch University, South Street, Murdoch, WA 6150, Australia

4 TSE Department, Animal Health and Veterinary Laboratories Agency, New Haw, Addlestone, Surrey KT15 3NB, UK

For all author emails, please log on.

BMC Veterinary Research 2013, 9:99  doi:10.1186/1746-6148-9-99

Published: 7 May 2013

Abstract

Background

Evidence for scrapie transmission from VRQ/VRQ ewes to lambs via milk was first reported in 2008 but in that study there were concerns that lateral transmission may have contributed to the high transmission rate observed since five control lambs housed with the milk recipients also became infected. This report provides further information obtained from two follow-up studies, one where milk recipients were housed separately after milk consumption to confirm the validity of the high scrapie transmission rate via milk and the second to assess any difference in infectivity from colostrum and subsequent milk. Protein misfolding cyclic amplification (PMCA) was also used to detect prion protein in milk samples as a comparison with the infectivity data and extended to milk samples from ewes without a VRQ allele.

Results

Seven pairs of lambs fed colostrum and milk individually from seven scrapie-affected sheep (pre-clinical or clinical) presented with disease-associated prion protein, PrPd, in rectal lymphoid tissue at 4–5 months of age. Five further pairs of lambs fed either colostrum or subsequent milk from five pre-clinical scrapie-affected sheep equally presented with PrPd in lymphoid tissue by 9 months of age. Nine sheep were lost due to intercurrent diseases but all remaining milk or colostrum recipients, including those in the original study with the lateral transmission controls, developed clinical signs of scrapie from 19 months of age and scrapie was confirmed by brain examination. Unexposed control sheep totalling 19 across all three studies showed no evidence of infection.

Scrapie PrP was amplified repeatedly by PMCA in all tested milk samples from scrapie-affected VRQ/VRQ sheep, and in one scrapie-affected ARQ/ARQ sheep. By contrast, milk samples from five VRQ/VRQ and 11 ARQ/ARQ scrapie-free sheep did not have detectable scrapie PrP on repeated tests.

Conclusions

Feeding of milk from scrapie-affected sheep results in a high transmission rate in VRQ/VRQ sheep and both colostrum and milk transmit scrapie. Detection of scrapie prion protein in individual milk samples from scrapie-affected ewes confirms PMCA as a valuable in vitro test.

Keywords:
Transmissible spongiform encephalopathy; Scrapie; Sheep; Milk; Colostrum; Transmission; PMCA; Prion protein; RAMALT; Copper