No cause of death has been released, but he had suffered for years from congestive heart failure, according to his biographer and former student, Dr. Robert Klitzman of Columbia University.
An energetic and intellectual researcher, Gajdusek often said he was more proud of his anthropological studies among the Fore and Anga people of Micronesia than he was of the research that brought him the ultimate prize.
But blinded by his hubris and self-admitted pedophilia, he spent the last decade of his life in exile in Europe after his arrest and imprisonment for molesting one of the more than 50 children he brought to the United States, adopted and educated.
Intrigued by his two years of studying rabies, plague, arbovirus infections and scurvy at the Institut Pasteur in Tehran, Gajdusek scoured the Hindu Kush, the jungles of South America and the mountains, swamps and high valleys of Papua New Guinea and Malaysia searching for a rare disease he could make his own.
He found it when he met Dr. Vincent Zigas, an Estonian medical officer who served the Fore people in eastern Papua New Guinea. Zigas introduced him to the Stone Age people, who were suffering from a mysterious malady that they called kuru, from the Fore word meaning "to shake."
The disease, which caused trembling, sporadic fits of laughter and madness before inevitably leading to death, affected one out of 10 people in the 35,000-member tribe. Autopsies showed that victims' brains were riddled with gaping holes, making their once solid organs resemble sponges -- leading to the general name spongiform encephalopathies for diseases in the class.
The disease was not believed to result from an infection, because victims did not suffer a fever and there were no signs of inflammation -- both indications of classical infections. Most researchers thought kuru was either hereditary or the result of a dietary deficiency.
Gajdusek described the disease in a 1957 issue of the New England Journal of Medicine and took samples back to his lab at the National Institutes of Health in Bethesda, Md., for study. He concluded that the disease was spread during an ancient funerary ritual when women and children consumed the brains of the deceased.
Since that practice was formally banned in 1959, no new cases of the disease have appeared except in those who were exposed before the ban took effect.
Gajdusek injected samples of diseased human brain tissue into a variety of small animals hoping to reproduce the disease, but without success.
He ultimately obtained some chimpanzees and injected them as well. At first, that too yielded no results. But after periods ranging from 1 1/2 to three years, the animals began to develop symptoms similar to those exhibited by the Fore.
In a 1966 paper in the journal Nature describing the transmission experiments, Gajdusek dubbed the infectious agent a "slow, unconventional virus."
Further studies by Gajdusek and others showed that a similar agent was responsible for a disease in sheep called scrapie, another malady in humans called Creutzfeldt-Jacob disease and the variant form of Creutzfeldt-Jacob commonly known as mad cow disease.
Eventually, neurologist Stanley Prusiner of UC San Francisco identified the infectious agent as an unexpected rogue form of protein called a prion -- a feat that won him his own Nobel Prize in 1997.
Prions are mis-folded forms of protein that, through mechanisms not yet understood, induce other proteins to assume similar shapes, disrupting cellular metabolism and killing cells in the brain.
Prions cannot be disrupted even in boiling water, are not susceptible to drug treatment and cannot be classified as living because they contain no DNA or RNA. They are also not recognized by the immune system as foreign, so the body cannot fight them off as it would any other infectious agent.
Some researchers now believe that prions may also be involved in producing dementia and perhaps even in triggering cancer. Gajdusek later helped other researchers find genetically isolated populations that helped shed light on the causes of hermaphroditism, Huntington's disease and other rare illnesses.
Daniel Carleton Gajdusek was born Sept. 9, 1923, in Yonkers, N.Y., the son of a Slovak father and a Hungarian mother. As a child, he demonstrated a remarkable interest and skill in science, stimulated by his aunt, Irene Dobroscky, who worked at the Boyce Thompson Institute for Plant Research in New York.
She tutored him in the biology of plants and the insects that infested them and introduced him to other researchers at the institute. During the summers of his 13th to 16th years, he worked in the laboratory of chemist John Arthur, synthesizing a variety of compounds that Arthur thought might have insecticidal properties.
One of those chemicals, 2,4-dichlorophenoxyacetic acid, became a commercial weed killer, and the institute based its patent claims on young Gajdusek's laboratory notebook.
He was an undergraduate at the University of Rochester, then entered Harvard Medical School, where he received his degree in 1946, specializing in pediatrics. His postgraduate education included work at Harvard, Columbia and Caltech, where he interacted with many of the notable biologists of the era.
In 1951, he was drafted into the Army and sent to the Walter Reed Army Medical Service Graduate School as a research virologist, spending time at the Tehran institute. Afterward, he went to Australia to perform postdoctoral work at the Walter and Eliza Hall Institute of Medical Research. It was on the way home from this interlude that he discovered the Fore, changing the course of his life forever.
Klitzman and others say Gajdusek mingled comfortably with the isolated tribes, communicating easily in a nonverbal fashion and becoming a de facto member of the tribes' extended families.
Some critics have charged that Gajdusek brought children from the tribes to the United States and adopted them to satisfy his pedophilia. But anthropologist Ceridwen Spark of Monash University in Australia, who studied Gajdusek, argues that it was his need for an extended family that led him to help the boys.
In any case, Gajdusek spent much of his own money raising the boys and educating them, sending some to graduate school and medical school on his own dime. But his efforts ultimately led to his downfall.
In 1996, one of his boys, by then an adult in college, went to the police alleging that when he was a teenager his adopted father had abused him. The FBI then recorded a call between the young man and Gajdusek in which the scientist admitted that he was a pedophile, that he had touched the boy sexually and that he had had sex with some of the other boys.
He named one other boy in the conversation, and the boy confirmed the story. But Gajdusek's friends helped the boy return to New Guinea, and authorities could prosecute only the offense against the boy who had gone to the police. On the advice of his lawyer, Gajdusek negotiated a plea bargain and in April 1997 was sentenced to 12 to 18 months in prison -- despite a stack of letters from prominent scientists begging the court for leniency.
He was released the following April and immediately left for France, spending the rest of his life working and writing in Europe. He apparently liked the long, dark winters of Tromso because the isolation gave him plenty of time for writing.
He remained unrepentant about his sexual relationships with the young boys. He often said he thought American law was unduly prudish and argued that he had chosen boys only from cultures where man-boy sex was common and unremarkable.
In addition to his many adopted sons and daughters, Gajdusek is survived by two nephews, Karl Lawrence Gajdusek and Mark Terry.