Reports by two research groups in last week's Nature Medicine showed that, at least in mice, the onset of the prion disease scrapie can be delayed. The studies help illuminate the mechanism by which prions spread, but therapeutic options are not around the corner, as the researchers' strategy only worked when small amounts of infectious material were used, and the animals were pretreated before being infected.

Transmissible spongiform encephalopathies (TSEs) like scrapie, mad cow disease, and new variant Creutzfeldt-Jakob disease (nvCJD) in humans are caused by abnormally folded prion proteins that find their way into the nervous system via a mechanism not yet fully understood. However, scientists have long suspected that the neuroinvasive