The deadly science of kuru: Why prions make cannibalism catastrophic

In the highlands of Papua New Guinea during the 1930s, Australian gold prospectors encountered a community of roughly eleven thousand people called the Fore. What they found was a mystery that would take decades to unravel: up to two hundred members of this tribe were dying each year from an illness no one could name or explain. The Fore called it kuru, a word meaning "shivering" or "trembling." Once the symptoms appeared, death followed swiftly.

The disease announced itself with a loss of balance. Victims found their legs no longer obeyed them, their coordination dissolving. Soon they lost command of their emotions too, laughing uncontrollably even as their bodies failed—which is why outsiders came to call it "the laughing death." Within a year of the first signs, patients could no longer stand, could not feed themselves, could not control their own bodily functions. In the end, they lay convulsing on the ground until they died. For years, researchers tested every hypothesis they could construct. They looked for poisons, for genetic causes, for infectious agents. Nothing fit. It was not until the early 1960s that a medical anthropologist named Shirley Lindenbaum, working from City University of New York, turned her attention to a practice the Fore had maintained in secret: ritual cannibalism.

When a Fore person died, their community would cook and consume the body as an act of love and respect—a way to honor the dead rather than leave them to rot in the ground. The women of the tribe would extract the brain, mix it with ferns, wrap it in bamboo tubes, and cook it. They ate it themselves and sometimes gave portions to their children. Lindenbaum's insight was simple but transformative: the disease was not in the air or the water. It was in the brain. Once researchers began investigating this connection, the biological consequences became clear and deeply disturbing.

In the United States, a team from the National Institutes of Health led by physician Daniel Carleton Gajdusek conducted an experiment that would change medicine. They injected brain tissue from infected Fore people into chimpanzees and watched as the animals developed kuru's symptoms months later. Gajdusek would win the Nobel Prize for this work, though he initially called the culprit a "slow virus." But it was not a virus. It was not a bacterium, fungus, or parasite. It was something entirely new to science: an infectious agent with no genetic material, capable of surviving cooking, and not technically alive at all. It was a protein.

By 1997, neuroscientist and biochemist Stanley Prusiner had identified the precise mechanism. The cause was a protein twisted into an abnormal shape—a prion. These warped proteins possessed an almost supernatural ability: they could force normal proteins on the surface of brain cells to twist into the same corrupted form, like a microscopic chain reaction of deformation. Prusiner also won the Nobel Prize for this discovery. Unlike viruses and bacteria, prions do not attack cells directly. Instead, they cause enough proteins to misfold that entire clusters of nerve cells die. The brain becomes riddled with holes, resembling a sponge. The result is a neurodegenerative disease that consumes the person until nothing remains.

The kuru epidemic likely began when a single Fore person spontaneously developed Creutzfeldt-Jakob disease, a prion disorder similar to kuru. When this person died and their infected brain was consumed, the disease passed to those who ate it. From there, it spread through generations, each ritual meal a transmission event. The Fore stopped practicing mortuary cannibalism more than fifty years ago, yet the last confirmed death from kuru did not occur until 2009. The epidemic was not officially declared over until 2012, more than seven decades after it began.

What makes prion diseases particularly alarming is how little we still understand them. They have incubation periods stretching across years or decades. They are difficult to study because of how long they take to manifest and how easily they transmit. And kuru was not the end of the story. After the last kuru death, a new prion disease emerged in cattle—bovine spongiform encephalopathy, known as mad cow disease—which also jumped to humans through contaminated meat. Researchers still do not fully understand why animals, including humans, carry these proteins in the first place, or what triggers them to misfold. The questions remain open, the mechanisms still mysterious. What is certain is that prions represent a category of infection unlike anything medicine had encountered before, and the threat they pose has not disappeared.