121. Kuru disease in human is caused by:
(a) Bacteria,
(b) Mycoplasma,
(c) Prions,
(d) Virus

Introduction

Kuru disease is a rare but fascinating and terrifying neurological disorder that has intrigued scientists for decades. While it is not caused by typical infectious agents such as bacteria, viruses, or mycoplasma, the underlying cause of Kuru lies in the realm of prions—misfolded proteins that induce other proteins to adopt an abnormal conformation. This article explores Kuru disease, its causes, and how prions differ from other more familiar pathogens.

What is Kuru Disease?

Kuru disease is a neurodegenerative disorder that was first discovered in the Fore people of Papua New Guinea in the 1950s. The disease primarily affects the brain, causing symptoms such as tremors, loss of coordination, and difficulty walking. As the disease progresses, individuals can experience severe cognitive decline and, ultimately, death.

The term “Kuru” means “to shake” in the Fore language, referring to one of the most prominent symptoms of the disease, which is uncontrollable shaking. It primarily affects individuals who participated in the practice of cannibalism, where the infected brain tissue of deceased individuals was consumed during funeral rites.

Kuru and Prions

The key to understanding Kuru disease lies in the concept of prions—infectious agents composed solely of protein. Unlike bacteria, viruses, and other pathogens, prions do not contain genetic material such as DNA or RNA. Instead, they are proteins that have folded abnormally. These misfolded proteins are capable of inducing other normally folded proteins to adopt their misfolded structure, creating a cascade effect.

Prions cause a range of diseases known as prion diseases or transmissible spongiform encephalopathies (TSEs), which include:

• Kuru disease

• Mad cow disease (Bovine spongiform encephalopathy)

• Creutzfeldt-Jakob disease (CJD)

• Scrapie (in sheep)

In Kuru, the disease is believed to have been transmitted through the consumption of infected human brain tissue, which contained these misfolded prion proteins.

Prions vs Other Infectious Agents

While prions are unique in their structure and mechanism of transmission, they can be compared to other infectious agents, such as bacteria, viruses, and mycoplasma. Here’s how they differ:

• Bacteria: These are single-celled microorganisms that can multiply and spread in the body. Bacteria typically have a well-defined structure, including a cell wall and genetic material (DNA). They can cause a wide range of diseases, from infections like tuberculosis to food poisoning.

• Viruses: Viruses are even smaller than bacteria and require a host cell to replicate. Unlike bacteria, viruses are composed of a small amount of genetic material (either DNA or RNA) surrounded by a protein coat. Diseases like the flu, HIV, and the common cold are caused by viruses.

• Mycoplasma: These are a group of bacteria that lack a cell wall. They are among the smallest living organisms and can cause infections, particularly in the respiratory system. Unlike prions, mycoplasma infections can be treated with antibiotics.

• Prions: Unlike all the above, prions are not living organisms. They are misfolded proteins that can induce other proteins to misfold. Prion diseases are typically fatal and are not treatable with conventional medications like antibiotics or antivirals.

How is Kuru Transmitted?

Kuru was once a significant health concern among the Fore people, as it was transmitted through the ritualistic consumption of human brain tissue. This practice of cannibalism led to the spread of the prion that caused Kuru. Once the connection between cannibalism and Kuru was established, the practice was abandoned, and the incidence of the disease significantly declined.

It is important to note that prion diseases like Kuru cannot be spread through casual contact. They require the direct ingestion of contaminated tissues to transmit the prions that cause the disease.

Symptoms and Diagnosis of Kuru

The symptoms of Kuru disease are progressive and include:

• Tremors: Uncontrollable shaking or trembling is one of the hallmark signs.

• Ataxia: Loss of coordination and balance.

• Dementia: Cognitive decline, including memory loss and confusion.

• Difficulty walking: Affected individuals may experience problems with movement and walking.

• Death: Eventually, the disease progresses to the point of causing death, usually within a year or two of symptom onset.

Diagnosis of Kuru typically involves a clinical examination, a history of exposure (in cases related to cannibalism), and testing to rule out other conditions. Brain autopsies in affected individuals often show the hallmark “spongiform” appearance of prion-induced damage to the brain tissue.

Conclusion

Kuru disease serves as a sobering reminder of how infectious agents can manifest in unconventional ways. While bacteria, viruses, and mycoplasma are more commonly known as causes of diseases, prions present a unique challenge to our understanding of infection and disease. As Kuru is caused by prions—misfolded proteins—it stands apart from other diseases that are caused by bacteria or viruses.

Understanding prions and prion diseases like Kuru has led to critical advancements in medical science, particularly in understanding neurodegenerative diseases. However, the nature of prions means they are still largely untreatable, making prevention and education crucial in managing their spread.