NIBBLING at the soil is their thing, but unfortunately for sheep, deer and elk that very habit could be spreading diseases that lay waste to their brains. The finding could explain why so many ruminants catch illnesses similar to mad cow disease and why fields appear to remain infectious many years after they are grazed.
A team led by Judd Aiken of the University of Wisconsin, Madison, has discovered that prions 鈥� the rogue proteins that cause BSE-like diseases 鈥� become 700 times more infectious when bound to the common soil mineral montmorillonite. The proof came from experiments in which hamsters were fed prions alone, or prions bound to the mineral. 鈥淚t took just 100 micrograms of bound prions to infect them 鈥� an amount the size of a pinhead,鈥� Aiken says. Hamsters fed the mineral-bound prions also developed disease much sooner than the pure prion group (PLoS Pathogens, ).
鈥淧rions become 700 times more infectious when bound to a common soil mineral鈥�
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Why the mineral makes prions more infectious is unclear, but it may help them pass more easily through animals鈥� gut walls, for example. The fear now is that tiny amounts of soil tainted with prions 鈥� perhaps from infected animal carcasses 鈥� might be enough to spread diseases like chronic wasting disease among deer and elk, and scrapie among sheep. If the mineral also helps prevent prions from degrading, fields may remain tainted for years, raising the issue of how to detect and decontaminate such pastures.
