"This is a dichotomy in our field, and maybe (the new research) is part of the answer."
In their studies, the Wisconsin researchers looked at the ability of prions to bind to different types of common soil minerals. One, known as montmorillonite, is a type of clay and prions seem to have a special affinity for latching onto the microscopic particles.
"We expected the binding of the montmorillonite to be the highest among the minerals we examined. However, we were surprised by the strength of the binding," notes Joel Pedersen, a UW-Madison professor of soil science who helped direct the new study.
The Wisconsin team also looked at the ability of the prion to bind to two other common soil minerals: quartz and kaolinite, another common clay mineral.
"We found binding of the abnormal protein to all three," says Aiken, "but the binding to montmorillonite was very avid, very tight. We found it very difficult to remove the prions from the montmorillonite."
Feeding the prion-mineral mix to hamsters, a common animal model for prion disease, Aiken's team expected to see a lower rate of infection than animals dosed with pure agent. Surprisingly, prions bound to montmorillonite were significantly more infectious than prions alone.
"We thought the binding might decrease infectivity," Aiken explains. "In each case, you add montmorillonite and we get more animals sicker and quicker than in the absence of montmorillonite clay."
What is occurring in soils in the woods and on the farm is unknown, says Pedersen, but the new findings may help begin to answer some key questions about how prions survive in the soil and retain their infectious nature, sometimes for years.
In the case of scrapie, the prion disease of sheep, observations of sheep pastures in the United Kingdom and Iceland have shown that animals introduced into pastures that on
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Contact: Judd Aiken
jma@svm.vetmed.wisc.edu
608-262-7362
University of Wisconsin-Madison
5-Jul-2007