Prions in Milk from Ewes Incubating Natural Scrapie
Caroline Lacroux1, Stéphanie Simon2, Sylvie L. Benestad3, Séverine Maillet2, Jacinthe Mathey1, Séverine Lugan1, Fabien Corbière1, Hervé Cassard1, Pierrette Costes1, Dominique Bergonier1, Jean-Louis Weisbecker4, Torffin Moldal3, Hugh Simmons5, Frederic Lantier6, Cécile Feraudet-Tarisse1,2, Nathalie Morel2, François Schelcher1, Jacques Grassi2, Olivier Andréoletti1*
1 UMR INRA ENVT 1225, Interactions Hôte Agent Pathogène, Ecole Nationale Vétérinaire de Toulouse, Toulouse, France, 2 CEA, Service de Pharmacologie et d'Immunoanalyse, IBiTec-S, DSV, CEA/Saclay, Gif sur Yvette, France, 3 National Veterinary Institute, Sentrum, Oslo, Norway, 4 INRA Domaine de Langlade, Pompertuzat, France, 5 VLA Weybridge, New Haw, Addlestone, Surrey, United Kingdom, 6 INRA IASP, Centre INRA de Tours, Nouzilly, France
Abstract Since prion infectivity had never been reported in milk, dairy products originating from transmissible spongiform encephalopathy (TSE)-affected ruminant flocks currently enter unrestricted into the animal and human food chain. However, a recently published study brought the first evidence of the presence of prions in mammary secretions from scrapie-affected ewes. Here we report the detection of consistent levels of infectivity in colostrum and milk from sheep incubating natural scrapie, several months prior to clinical onset. Additionally, abnormal PrP was detected, by immunohistochemistry and PET blot, in lacteal ducts and mammary acini. This PrPSc accumulation was detected only in ewes harbouring mammary ectopic lymphoid follicles that developed consequent to Maedi lentivirus infection. However, bioassay revealed that prion infectivity was present in milk and colostrum, not only from ewes with such lympho-proliferative chronic mastitis, but also from those displaying lesion-free mammary glands. In milk and colostrum, infectivity could be recovered in the cellular, cream, and casein-whey fractions. In our samples, using a Tg 338 mouse model, the highest per ml infectious titre measured was found to be equivalent to that contained in 6 µg of a posterior brain stem from a terminally scrapie-affected ewe. These findings indicate that both colostrum and milk from small ruminants incubating TSE could contribute to the animal TSE transmission process, either directly or through the presence of milk-derived material in animal feedstuffs. It also raises some concern with regard to the risk to humans of TSE exposure associated with milk products from ovine and other TSE-susceptible dairy species.
Author Summary A decade ago, a new variant form of Creutzfeldt-Jakob disease was identified. The emergence of this prion disease in humans was the consequence of the zoonotic transmission of bovine spongiform encephalopathy through dietary exposure. Since then, the control of human exposure to prions has become a priority, and a policy based on the exclusion of known infectious materials from the food chain has been implemented. Because all investigations carried out failed to reveal evidence of infectivity in milk from affected ruminants, this product has continuously been considered as safe. In this study, we demonstrate the presence of prions in colostrum and milk from sheep incubating natural scrapie and displaying apparently healthy mammary glands. This finding indicates that milk from small ruminants could contribute to the transmission of prion disease between animals. It also raises some concern with regard to the risk to humans associated with milk products from ovine and other dairy species.
Citation: Lacroux C, Simon S, Benestad SL, Maillet S, Mathey J, et al. (2008) Prions in Milk from Ewes Incubating Natural Scrapie. PLoS Pathog 4(12): e1000238. doi:10.1371/journal.ppat.1000238
Editor: Umberto Agrimi, Istituto Superiore di Sanità, Italy
Received: July 1, 2008; Accepted: November 12, 2008; Published: December 12, 2008
Copyright: © 2008 Lacroux et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was financially supported by GIS infections à prion (French Research Ministry), EU FAIR (QLK-CT 2001-390), and DEFRA (SE2004, contract: CSA 6914).
Competing interests: The authors have declared that no competing interests exist.
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Prions in Milk from Ewes Incubating Natural Scrapie
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