Kuru is transmitted by eating infected human brain tissue. Specifically, it spread through a funeral practice among the Fore people of Papua New Guinea, who consumed the brains of deceased relatives as part of mourning rituals. The infectious agent is a prion, a misfolded protein that cannot be destroyed by cooking and causes fatal, irreversible brain damage.
The Ritual That Spread the Disease
Kuru spread through endocannibalism, the practice of consuming the body of a deceased family member as an act of mourning and respect. Among the Fore people, when someone died, relatives would prepare and eat parts of the body. Women and children typically consumed the brain, which carries the highest concentration of infectious prions. Men generally preferred muscle tissue, which contained far less of the misfolded protein.
This difference in which body parts people ate had a dramatic effect on who got sick. Women and children of both sexes made up the vast majority of kuru cases, while adult men were largely spared. At its peak in the 1940s and 1950s, kuru killed so many women that it distorted the entire population structure of affected villages, where mortality rates reached as high as 35 per 1,000 people. Children orphaned by their mothers’ deaths frequently died of malnutrition, since the Fore did not traditionally transfer nursing children to another woman.
What Prions Are and Why They’re Dangerous
Unlike bacteria or viruses, prions contain no DNA or RNA. A prion is simply a normal brain protein that has folded into the wrong shape. Once inside the body, it forces healthy copies of the same protein to misfold as well, creating a chain reaction. The misfolded proteins clump together and gradually destroy brain tissue, leaving it riddled with tiny holes (the reason prion diseases are called “spongiform” encephalopathies).
What makes prions especially dangerous is their durability. Their tightly packed structure resists the enzymes your body uses to break down proteins, and conventional cooking temperatures do not neutralize them. This meant that even when Fore people cooked tissue before eating it, the prions survived intact and remained infectious.
How Prions Travel From the Gut to the Brain
When someone swallowed prion-contaminated brain tissue, the misfolded proteins passed through the stomach and reached the lining of the small intestine. There, specialized cells in the gut wall transported them across the intestinal barrier. Some of these cells are designed to sample the contents of the gut and pass material to the immune system, which inadvertently gave prions a way through.
Once past the intestinal lining, immune cells carried the prions to nearby lymphoid tissue, clusters of immune cells scattered throughout the gut. From there, the prions made contact with nerve fibers in the gut’s own nervous system. They then traveled backward along nerve pathways, climbing through the autonomic nervous system (the network that controls digestion, heart rate, and other involuntary functions) until they reached the spinal cord and brain. This entire process unfolded silently, over years or even decades, before any symptoms appeared.
Incubation Periods Lasting Decades
One of the most striking features of kuru is how long it can hide. After cannibalistic practices ended in the late 1950s, researchers expected cases to stop appearing within a few years. Instead, new patients continued to surface for decades. A study published in The Lancet found minimum incubation periods of 34 to 41 years among patients who developed kuru in the 21st century. In men, the likely incubation period ranged from 39 to 56 years, meaning some individuals carried the infection for over half a century before becoming ill.
This extraordinary latency made kuru one of the longest-incubating infectious diseases ever documented. It also complicated efforts to track the epidemic’s true end, since each new case decades after exposure raised the question of whether more might follow.
Why Some People Never Got Sick
Not everyone exposed to kuru developed the disease. Researchers studying Fore survivors discovered a genetic variant that provided powerful protection. A single amino acid change in the prion protein gene, known as G127V, appeared exclusively in this population and was under strong evolutionary selection during the epidemic. People who carried even one copy of this variant were essentially immune to kuru. The mutation is so effective that in laboratory models, it blocks prion disease as completely as having no prion protein at all.
This variant exists nowhere else in the world, and the fact that it was concentrated among the Fore strongly suggests it was driven to higher frequency by the intense selective pressure of the epidemic itself. People with the protective gene survived and had children; those without it were more likely to die.
How Kuru Progresses
Once symptoms begin, kuru follows a predictable and fatal course. Early on, patients develop an unsteady gait and tremors, particularly a characteristic shivering that gave the disease its name (“kuru” roughly translates to “shaking” in the Fore language). At this stage, patients can still walk, though with difficulty.
As the disease advances, coordination worsens until patients can no longer stand or walk without support. Involuntary muscle jerks become more frequent. In the final stage, patients are bedridden, unable to speak or swallow, and develop severe wasting. Death typically follows within 6 to 12 months of symptom onset. There is no treatment and no way to slow the progression once it begins.
Post-mortem examination of the brain reveals the hallmark damage: widespread deposits of misfolded prion protein forming distinctive round plaques throughout the brain tissue, along with the characteristic sponge-like holes caused by neuron death.
Why Kuru No Longer Exists
Australian colonial authorities banned cannibalistic practices among the Fore in the late 1950s. As the practice stopped, so did new transmission. Children born after 1954 in the South Fore region almost never developed kuru, confirming that the ritual was the sole route of spread. Cases continued to appear for decades afterward due to the extraordinarily long incubation period, but each year the average age of new patients rose, reflecting the shrinking pool of people who had been exposed before the ban.
The end of cannibalism effectively ended kuru. No new transmission has occurred in over 60 years, and the disease is now considered extinct in practice. Its legacy, however, reshaped science’s understanding of prion diseases and demonstrated that a misfolded protein alone, without any genetic material, can act as an infectious agent capable of spreading through an entire population.