In Pursuit of Prions
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Gajdusek never did discover how the Fore were getting kuru. In the early 1960s the anthropologist Shirley Glasse and her husband Robert would trace it to mortuary cannibalism. But by that time Gajdusek had left the Fore region for the NIH to continue working on the disease. Gajdusek thought the disease was hereditary, but he was not sure. Then in 1959 he got some important new information.
An American veterinary pathologist working in England named William Hadlow happened to see an exhibit on kuru at the Wellcome Medical Museum in London that included photographs of the victims’ brains. He felt as if he were seeing the same scrapie slides he had in his lab and wrote a note to the Lancet, the British medical journal, about the coincidence. He also sent a copy of his letter to Gajdusek.
Two things were known about scrapie by then: It could be transmitted, and it took a long time for the symptoms to show up. Those findings gave Gajdusek a clue. He threw himself into trying to prove that kuru was infectious, injecting homogenate made from the brains of kuru victims into everything from mice to hamsters to chimpanzees. Finally, in June 1965, Georgette, one of the chimps who had been injected with kuru tissue 21 months before, began to show the signs, “dragging herself around, shaking, looking for all the world like a kuru patient,” in the words of Michael Alpers, the head of the research program. After the chimp died, Gajdusek asked a British pathologist expert in scrapie to examine the chimp’s brain. What the pathologist saw reminded her of what she had seen in kuru victims. The chimp appeared to have died of the disease that killed the Fore. It was a moment of triumph for Gajdusek and his lab. Here was proof that kuru was an infectious disease, though Gajdusek had no idea what the nature of the infection was—bacterium, virus, protozoan or some other infectious agent.
Gajdusek was intrigued by Klatzo’s comparison of kuru to CJD, so he began inoculating healthy chimps with tissue from sufferers of CJD as well. Ultimately, these chimps also grew sick. When the animals died, pathologists examined their brains and saw that the sponginess and the holes resembled those of both kuru and scrapie victims.
One, as the saying goes, was a novelty; two was a coincidence; three—scrapie, kuru, CJD—was a theory. These long-ignored diseases, Gajdusek declared in the late 1960s, shared a cause, some sort of hard-to-destroy, slow-acting virus. The key sticking point was the word virus. Viruses are essentially bits of nucleic acid covered by protein; they insert themselves into cells and trick the cell’s reproductive apparatus into copying them. They generally provoke an immune reaction in their unwilling host, and it is these reactions that usually reveal the strain of the virus. Though they are not technically alive, viruses do contain bits of DNA or RNA, so they can be deactivated by the same techniques that kill living things—everything from washing with soap and water to heating to irradiation. And most viruses, once they are removed from the cell that they are parasitizing, die on their own, often in a few hours.
Gajdusek’s “odd, slow viruses,” as he called them, didn’t fit this description: Heat, formalin and disinfectants did not harm them. Even stranger, radiation did not diminish their virulence. But the agent seemed to have strains—some sheep with scrapie had a lot of trembling; others had an unrelenting itch. These facts added up to a very strange infectious agent: an indestructible strain-specific particle that didn’t die under conditions that would kill a virus and provoked no immune system response.
What was this particle? Gajdusek did not go as far as other researchers who posited that it was no virus at all. Experiments with centrifuges had turned up a lot of protein but no nucleic acid. Was it because there wasn’t any in the infectious agent? Could an infectious agent be entirely made of protein?
The conventional wisdom said no. Proteins are building blocks and engines and messengers of the body, but they are not alive. And to suggest, as some researchers began to, that a protein could make copies of itself in the victim’s body—that a nonliving agent was somehow replicating itself or being replicated in the victim’s body without DNA and causing disease—pushed up against the impossible.
