Is the prion protein PrPSc present in milk products? If the answer is yes, then what are the health implications regarding human consumption? Here, we summarize the findings of several scientific publications on this topic and discuss the implications.
To date, prion infectivity has been detected in the milk of sheep. Infected ewes can transmit scrapie, as the disease is called in sheep, via milk to other sheep. Recently, the disease-specific prion protein (PrPSc) has been detected for the first time in sheep milk. More importantly, it was found in the milk 20 months before the animal developed clinical signs of scrapie. This prion protein has been found in minute quantities and was only detectable in milk after amplification using the sPMCA technique. Prions were found in the milk of sheep of various genetic backgrounds, including those that are susceptible to scrapie and those that are generally thought to be resistant to scrapie.
What are the implications of finding prions in milk?
Scrapie has been known for centuries and does not appear to be transmissible to humans. However, these recent findings raise the question of whether sheep milk should be used in animal feed that is fed to a variety of animal species, as the milk could be a source of prion infection. Secondly, these findings also raise a broader question concerning the safety of milk for human consumption. Results from past studies and epidemiological data do not indicate that milk could be a major transmission route and prion proteins have never been detected in cow’s milk. However, the normal prion protein, PrPC, has been found in bovine milk and given the high dietary exposure of humans to dairy products, it makes it worthwhile to have a closer look at prions in cow’s milk.
