D. Carleton Gajdusek, a virologist who won the 1976 Nobel Prize in medicine for his work on the mysterious epidemics now known as prion diseases, died last week in Tromso, Norway.
The cause of death is unknown, but Dr. Gajdusek (pronounced GUY-dah-shek) was 85 and had long had congestive heart failure, said Dr. Robert Klitzman, his biographer, who said he had spoken to him about a week ago. He was found in his Tromso hotel room on Friday morning about 24 hours after a manager saw him at breakfast.
In later life, Dr. Gajdusek became notorious when he was charged with molesting the many young boys he had adopted in New Guinea and Micronesia and brought to live with him in Maryland. He pleaded guilty to one charge, served a year in prison and left the United States in 1998, dividing his time between Paris, Amsterdam and Tromso.
Dr. Gajdusek won the Nobel for his work on kuru, which was slowly wiping out the Fore tribe of New Guinea. Victims descended into trembling and madness before death and, after an autopsy, were found to have brains shot through with spongy holes.
In 1957, Dr. Gajdusek -- who had searched the Hindu Kush, the Amazon jungle and finally the mountain valleys of New Guinea hoping to find remote tribes with unique diseases to study -- realized that the victims had all participated in ''mortuary feasts'' in the decades before the custom was suppressed in the 1940s by missionaries and the Australian police.
The Fore, who lived as they had in the Stone Age, cooked and ate the bodies of tribe members who had died, and smeared themselves with the brains as a sign of respect for the dead.
The disease confounded explanation because the mashed brains of the victims, injected into chimpanzees' brains, produced no symptoms. All known disease-causing bacteria, viruses and parasites produced symptoms within days or weeks. But when the chimps developed kuru two years later, Dr. Gajdusek theorized that a slow-acting virus was at work, somehow not producing the expected immune reactions.
One of his assistants found ''scrapie-affiliated particles'' -- fibrils resembling those in the brains of sheep with scrapie. But it was Stanley B. Prusiner who identified them as tangles of normal proteins that had misfolded and clumped, ''teaching'' other proteins to follow; he named them prions. They are now recognized as the cause of kuru, scrapie, human Creutzfeldt-Jakob disease and bovine spongiform encephalopathy, better known as mad cow disease. Dr. Prusiner won his own Nobel in medicine for that work in 1997.
The idea that disease could be transmitted by a mere twisted protein -- something that lacks DNA and RNA and therefore cannot be said to be alive, is not killed by boiling and is not recognized as foreign by the immune system -- turned the scientific world on its ear. Such proteins are now suspected as the causes of dementias and possibly as triggers for cancer.
There has been a struggle even to find metaphors to elucidate the concept. Dr. Gajdusek once described the amyloid plaques of Alzheimer's as a wrecked cassette, spinning out tangles of protein faster than the brain can reel in the tape and chop it up. Kurt Vonnegut told Dr. Klitzman that he got his idea for Ice-9, a crystal that ''teaches'' water to harden into ice, freezing the world to death, from kuru.
Dr. Gajdusek also helped other researchers find small, long-intermarried populations with diseases to study, including work that helped establish the genetic basis of Huntington's disease and causes of hermaphroditism.
Dr. Klitzman, a professor of psychiatry at Columbia University, wrote ''The Trembling Mountain,'' an account of his time as a graduate student under Dr. Gajdusek in New Guinea. His brain ''worked faster and at a higher level than anyone's I've ever met,'' he said, and the researcher was friends with Buckminster Fuller, Linus Pauling and Oliver Sacks, whom Dr. Klitzman said suggested the biography.
Dr. Gajdusek was born on Sept. 9, 1923. He grew up in Yonkers and went to the University of Rochester and Harvard Medical School. From 1970 until his arrest in 1997, he headed the brain studies laboratory at the National Institute of Neurological Disease and Stroke, which is part of the National Institutes of Health.
Dr. Gajdusek was difficult and eccentric. In exile, he spent the winters in Tromso, which is above the Arctic Circle and dark 24 hours a day, because it was isolated and he got more work done.
He also remained unrepentant about the sexual relationships with his adopted sons, Dr. Klitzman said. He considered American law prudish and pointed out that sex with young men was normal in the cultures he studied and in the classic Greek societies at the foundation of Western civilization.
His legal assistant, Dorrie Runman, who was previously married to one of his sons, John Runman, said Dr. Gajdusek's survivors included ''his adopted sons and daughters, including Yavine Borimaand Jesse Mororui-Gajdusek in the United States, and two nephews, Karl Lawrence Gajdusek and Mark Terry.''
His children were legally adopted, Ms. Runman said. He put several through college and graduate or medical school. Some of them, now in their 50s, supported him during his legal troubles, while one sibling testified against him.