The Shaking Sickness
In the mid-20th century, a mysterious illness emerged among the Fore people in the mountainous Okapa District of Papua New Guinea. They called it "kuru," their word for "to shake" or "tremble." The disease began with an unsteady gait and headaches, then progressed to uncontrollable tremors, slurred speech, and sporadic, pathological bursts of laughter, which led to the name "laughing sickness." Kuru was always fatal, typically within a year of the first symptoms appearing.
The illness disproportionately affected women and children. At the epidemic's peak in the late 1950s, some villages lost up to 2% of their population annually, and the gender imbalance became severe, with some communities having two or three men for every woman. Initial investigations by Australian and American researchers, including Vincent Zigas and D. Carleton Gajdusek who first described the disease in Western medicine in 1957, were baffled. The Fore people believed the cause was sorcery.
An Infectious Protein
The breakthrough came from a combination of anthropology and virology. Researchers Shirley Lindenbaum and Robert Glasse were the first to formally hypothesize that kuru spread through the Fore's practice of endocannibalism—consuming relatives as part of a mourning ritual. This practice, known as transumption, was meant to free the spirit of the dead. Women and children were the primary participants in these mortuary feasts and they typically consumed the brain and spinal cord, where the infectious agent was most concentrated. Men, who consumed muscle tissue, were largely spared.
In 1963, Gajdusek sent brain tissue from an 11-year-old Fore girl who had died of kuru to his lab at the U.S. National Institutes of Health. There, he and his team inoculated chimpanzees with the tissue. After an incubation period of nearly two years, a chimpanzee named Daisy developed kuru, proving the disease was transmissible. This work earned Gajdusek the Nobel Prize in Physiology or Medicine in 1976.
The infectious agent itself remained a puzzle. It contained no DNA or RNA and was resistant to conventional sterilization. In 1982, neurologist Stanley Prusiner identified the culprit as a misfolded protein he named a "prion" (proteinaceous infectious particle). Prions propagate by causing normally folded proteins in the brain to change shape, setting off a chain reaction that creates sponge-like holes in the brain tissue. This discovery of an infectious agent without genetic material earned Prusiner a Nobel Prize in 1997. The Australian administration banned cannibalism in the 1950s, and the epidemic slowly vanished. The last known person to die from kuru passed away in 2009.