Prion Protein in Milk

BACKGROUND Prions are known to cause transmissible spongiform encephalopathies (TSE) after accumulation in the central nervous system. There is increasing evidence that prions are also present in body fluids and that prion infection by blood transmission is possible. The low concentration of the proteinaceous agent in body fluids and its long incubation time complicate epidemiologic analysis and estimation of spreading and thus the risk of human infection. This situation is particularly unsatisfactory for food and pharmaceutical industries, given the lack of sensitive tools for monitoring the infectious agent. METHODOLOGY/PRINCIPAL FINDINGS We have developed an adsorption matrix, Alicon PrioTrap, which binds with high affinity and specificity to prion proteins. Thus we were able to identify prion protein (PrP(C))--the precursor of prions (PrP(Sc))--in milk from humans, cows, sheep, and goats. The absolute amount of PrP(C) differs between the species (from microg/l range in sheep to ng/l range in human milk). PrP(C) is also found in homogenised and pasteurised off-the-shelf milk, and even ultrahigh temperature treatment only partially diminishes endogenous PrP(C) concentration. CONCLUSIONS/SIGNIFICANCE In view of a recent study showing evidence of prion replication occurring in the mammary gland of scrapie infected sheep suffering from mastitis, the appearance of PrP(C) in milk implies the possibility that milk of TSE-infected animals serves as source for PrP(Sc).