What Is Kuru?

Kuru is an extremely rare illness caused by a contagious protein (prion) found in the brain tissue of people with the disease. The only way to acquire kuru is to ingest this tissue or have the prion enter through an open wound.

Kuru was first identified in the Fore tribe in the highlands of New Guinea in the southwestern Pacific. Kuru was first discovered in the early 1950s but likely started about 50 years prior, at the turn of the 20th century.

People in this population had a ritual of eating the tissues of their dead, including the brains. Some of those who ate the brains of people who died from kuru got the illness themselves. In 1960, the New Guinea government discouraged the ritual, the practice stopped, and the disease declined.

Kuru caused about 200 deaths per year when first discovered. Cases of kuru were reported for many years afterward because the disease has a long incubation period. This number dropped sharply until there were few or no deaths each year. 

The last known person with kuru died in 2009. Estimates suggest there are around 2,700 recorded cases of people dying of kuru. The condition has since disappeared.

This article will review the history of kuru, its symptoms, and its prognosis.

Kuru Symptoms

Kuru causes the brain tissue to erode to the point at which it develops microscopic holes, making the tissue look like a sponge. It targets the cerebellum, the part of the brain that controls coordination.

"Kuru" is the Fore word for "shiver," and one of the main symptoms is movement issues. These include:

• Unsteady gait or clumsiness (ataxia)
• Tremor or muscle jerks
• Slurred speech
• Mood changes
• Arm and leg pain
• Worsening coordination problems
• Difficulty walking
• Headache
• Difficulty swallowing 
• Malnutrition or starvation from being unable to feed oneself

One of the frightening characteristics of prion disease is the amount of time between exposure and symptoms. People may live for many years or decades before showing signs.

Causes

Kuru is a prion disease. It is also called transmissible spongiform encephalopathy (TSE). Prion protein is called PrP and coded in the gene PRNP. Its function is unknown, but it is present in tissues all over the body. 

Prions are contagious misfolded proteins. If misfolded prion protein comes in contact with normally folded prion protein, it can bend them out of shape.

This bending makes them:

• Not work correctly
• Clump together
• Able to fold other prions out of shape
• Toxic to the brain
• Almost impossible to destroy

Because misfolded proteins cause prion diseases, they're sometimes called conformational diseases. The theory is that at the root of some of these diseases are misfolded proteins that don't work right or build up and become toxic. The best-known conformational disease is Alzheimer's, but it may be implicated in many others.

Kuru occurred at epidemic levels in the 1950s among the Fore people in the highlands of New Guinea, a population with a tradition of eating the brains of their dead.

It's likely that one person spontaneously developed the genetic prion disease Creutzfeldt-Jakob. That brain was ingested by others in the tribe during the ritual, spreading the prion to their brains and causing kuru.

You can't get kuru from eating animal brains. But you can acquire animal prion diseases from infected animals. For example, the mad cow outbreak happened when people ate meat contaminated with nervous system tissue from cows with bovine spongiform encephalopathy (BSE), a prion disease.

By 2019, more than 200 people worldwide had acquired a prion disease from eating beef tainted with BSE, and they all have died.

Prions are especially dangerous because the normal methods used to kill viruses, bacteria, and other pathogens like heat, cold, soaps, and acids don’t work on prions.

For a long time, experts thought that very strong disinfectants or sustained heat for several hours at extremely high temperatures (900 degrees F and above) was the only way to destroy prions.

But in the last few years, researchers have found that a nontoxic hypochlorous acid solution can disinfect prions. This is great news for hospitals that have had just to throw away prion-contaminated surgical tools in the past.

Diagnosis

Kuru has never been diagnosed directly. New tests may be able to detect cases of kuru if there is ever another outbreak. Traditionally, healthcare providers used neurological exams to detect changes in coordination and show deteriorating walking and other abilities. 

Other advanced diagnostic technologies that weren’t around in the 1950s and 1960s may also have been able to detect kuru. Brain magnetic resonance imaging (MRI) can show features suggestive of prion disease, so it could help diagnose a case of kuru should one occur.

Tests for prion disease also typically include an analysis of the fluid in the spinal cord. Cerebrospinal fluid tests include:

• 14-3-3 and Tau tests are biomarkers of rapid brain breakdown. They can be used to gauge the probability of prion disease but are not specific to prions.
• RT-QuIC, the real-time quaking-induced conversion test, is the only prion-specific test used to diagnose prion disease. This test amplifies otherwise undetectable levels of prions to the point where they can be easily detected.

Other than these tests, a brain biopsy is the only way to detect a prion disease, but it is generally discouraged. In a biopsy, a sample of tissue is removed and analyzed microscopically in the lab.

Treatment

There are no treatments to control or cure kuru or any other prion disease. The best treatment for kuru is prevention—discouraging the practice of cannibalism The last case of kuru was in 2009.

Prognosis

Kuru has a long incubation period. It can take years or even decades after infection for a person to develop symptoms. The average incubation period is 10 to 13 years, but incubation periods of 50 years or even longer have been seen.

As their cerebellum is destroyed, people with kuru lose their ability to stand or eat. They die in a coma about six to 12 months after the first symptoms.

Summary

Kuru is an extremely rare disease. It's caused by a contagious protein found in the brain tissue of infected humans. The only way to contract the disease is by ingesting or having contact with contaminated brain tissue.

Researchers first found the disease in a New Guinea tribe that had a ritual of eating their dead. The number of cases sharply decreased when the government discouraged this practice in 1960. The last known kuru death occurred in 2009.

The disease causes the brain tissue in the cerebellum to erode. It results in unsteady movement, tremors, slurred speech, and mood changes.

Kuru is a prion disease, also known as transmissible spongiform encephalopathy. It is caused by contagious misfolded proteins. These proteins clump together, fold other prion proteins out of shape, and are very hard to destroy.

There are five known prion diseases in humans, with kuru being the first identified. The best-known animal prion disease is BSE, or mad cow disease. Humans contract variant Creutzfeldt-Jakob disease by eating contaminated meat from cows with BSE.