SCIENCEThe Real Reason Prion Diseases Spread Without DNA8 min read

A Brain Disease With No Identifiable Cause

For much of the twentieth century, a cluster of fatal brain diseases defied every known rule of infection. They destroyed nervous tissue, left brains riddled with holes visible under a microscope, and spread between animals and humans — yet no bacterium, no fungus, and no virus could be isolated from affected tissue. Scientists were dealing with something that behaved like an infectious agent but carried none of the biological machinery infection was supposed to require. The puzzle sat at the edge of medicine for decades, waiting for someone stubborn enough to chase it down. That person turned out to be a neurologist at the University of California, San Francisco, and his 1982 paper in the journal Science rewrote the basic rules of how diseases can spread.

The Patient Who Launched a Career

Stanley Prusiner was a neurology resident when he watched a patient die from Creutzfeldt-Jakob disease, a degenerative brain disorder, within two months of her first symptoms. What struck him was not just the speed of the decline, but the absence of anything that should have been there. No fever. No elevated immune markers. No sign that the body recognized a threat at all. Yet the disease was destroying her brain while leaving the rest of her body untouched. He had been told she was infected by a so-called slow virus, a pathogen that progressed on unusually long timescales. That explanation never satisfied him, and the image of that patient stayed with him through the years that followed, eventually pushing him to study a similar disease in sheep called scrapie.