Kuru · What Is It, Causes, Signs and Symptoms, and More

Kuru is a rare and fatal infectious disease affecting the nervous system first found among individuals in Papua New Guinea. The infection is typically transmitted from person-to-person during ritual cannibalism.  

Kuru is a type of spongiform encephalopathy, which is a group of diseases that causes brain tissue to degenerate and replacement of healthy tissue with clusters of tiny liquid-filled, thin-walled cavities called cysts. The brain of an individual with kuru tends to look like a sponge.  

Kuru is caused by the accumulation of infectious, misfolded proteins called prions in the nervous system. The disease is spread through cannibalism of infected tissue. Kuru first affected a tribe in the highlands of New Guinea who ate the brain tissues of deceased family members. The misfolded prion proteins were thereby passed from person-to-person.  

Kuru has a very long incubation period (i.e., time between exposure to infectious agent and onset of signs and symptoms), which is typically around 10 to 13 years but can be up to 50 years.  

Signs and symptoms of kuru vary depending on the stage of the disease. Early stages of kuru are characterized by tremors, unsteady gait, and ataxia (i.e., impaired coordination of movements). As the disease progresses, tremors and ataxia increase in frequency and intensity, and muscle jerks (i.e., quick, involuntary movements) may also develop. Other signs and symptoms may also include pain in the upper and lower extremities, difficulty walking, slurred speech, and headache.  

Kuru is also associated with emotional instability resulting in uncontrollable outbursts of laughter or crying for no reason, explaining why it was also known as “the laughing sickness”. In the late stages of kuru, individuals may also develop dementia or experience difficulty swallowing, or dysphagia, which can lead to malnutrition. Eventually, individuals with kuru end up in a coma. 

Differential diagnoses involve considering various possible conditions that could be causing symptoms and then ruling out each one through use of history, clinical evaluation, diagnostic tests, and critical thinking. This process helps to narrow down the list of potential diagnoses to determine the most likely cause of the symptoms.  

Differential diagnoses can be broken down into four categories: most likely, less likely, least likely, and can’t miss. Most likely diagnoses are conditions most probable based on symptoms and clinical presentation. Less likely diagnoses are not as probable but should still be considered. On the other hand, least likely diagnoses can be considered if other, more probably conditions are excluded. Finally, can’t miss diagnoses are less common but critical to promptly identify and treat as they can lead to severe consequences.  

• Creutzfeldt-Jakob disease (CJD): A prion disease with similar neurodegenerative symptoms, including rapid cognitive decline, myoclonus, and ataxia. 
• Gerstmann-Sträussler-Scheinker (GSS) disease: Another prion disease presenting with progressive ataxia and dementia. 
• Fatal familial insomnia (FFI): A prion disease characterized by severe insomnia, autonomic dysfunction, and motor abnormalities.  

• Lewy body dementia: A neurodegenerative disorder with symptoms of dementia, visual hallucinations, and parkinsonism, but without the rapid progression seen in prion diseases.  
• Huntington disease: A genetic disorder causing movement disorders, cognitive decline, and psychiatric symptoms, but with a slower progression.  
• Viral encephalitis: Inflammation of the brain caused by viral infections, presenting with fever, headache, and neurological deficits.  

• Mercury toxicity: Can cause neurological symptoms but typically includes other signs of heavy metal poisoning.  
• Thyroid dysfunction: Can cause cognitive and motor symptoms, but usually presents with other systemic signs.   

• HIV-associated CNS conditions: Includes various neurological complications in individuals with HIV, requiring prompt diagnosis and treatment. 
• Subacute sclerosing panencephalitis (SSPE): A rare, progressive brain disorder caused by a persistent infection with the measles virus. 

There is no cure for kuru, and death usually occurs within 6 to 12 months from symptom onset. Treatment is only supportive and can include analgesics and physical therapy to assist with movements.   

Prevention involves stopping cannibalism, which has eradicated new kuru cases.