Scrapie infectivity has not been detected in milk, but cellular prion protein, the precursor of the disease-associated protein PrPd, has been found in milk from ruminants
Scrapie can be transmitted to lambs through milk, according to a study by researchers in the UK. The finding suggests that the risk of scrapie transmission via milk may be higher than previously thought, and that other prion diseases could be transmitted in sheep via milk. 
Photo: Shelley Cunningham
Scrapie infectivity has not been detected in milk, but cellular prion protein, the precursor of the disease-associated protein PrPd, has been found in milk from ruminants. To determine whether milk can transmit scrapie, researchers from the Veterinary Laboratories Agency in Weybridge, UK, fed milk from scrapie-affected ewes to 18 lambs that were genetically susceptible to the disease.
Three of the lambs were culled and two were found to have PrPd in their intestinal tissues. The protein was also found in samples of the lymphoid tissue of the gut taken from the surviving lambs, as well as in some control lambs mixed with the scrapie milk recipients after weaning. This suggested that the lambs that had received the infected milk were able to shed the infectious agent and infect other lambs. There was no sign of PrPd in tissue samples from a control group housed in the same building but fed milk from healthy ewes.
The researchers pointed out that the finding should have no direct implications for human health. Scrapie has not been shown to be transmissible to humans, and bovine spongiform encephalopathy has not been found naturally in sheep. However, the study helps to explain how prion diseases of sheep are transmitted, and could help inform measures to protect human health if BSE were to be found in sheep.
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