Kuru is a very rare, incurable disorder that was formerly common among the Fore people of Papua New Guinea.
It is widely accepted that kuru was transmitted among members of the Fore tribe of Papua New Guinea via funerary cannibalism. Deceased family members were traditionally cooked and eaten, which was thought to help free the spirit of the dead. Females and children usually consumed the brain, the organ in which infectious prions were most concentrated, thus allowing for transmission of kuru. The disease was therefore more prevalent among women and children.
The term kuru derives from the Fore word kuria or guria (“to shake”), due to the body tremors that are a classic symptom of the disease and kúru itself means “trembling”. It is also known as the “laughing sickness” due to the pathological bursts of laughter which are a symptom of the disease.
While the Fore people stopped eating human meat in the early 1960s, when it was first speculated to be transmitted via endocannibalism, the disease lingered due to kuru’s long incubation period of anywhere from 10 to over 50 years. The epidemic declined sharply after discarding cannibalism, from 200 deaths per year in 1957 to 1 or no deaths annually in 2005, with sources disagreeing on whether the last known kuru victim died in 2005 or 2009.
Signs and symptoms
Kuru is a disease of the nervous system that causes physiological and neurological effects which ultimately lead to death.
The incubation period averages between 10–13 years, but can be as short as 5 and has been estimated to last as long as 50 years or more after initial exposure. The youngest individual recorded to have kuru was 12 years old.
The clinical stage, which begins at the first onset of symptoms, lasts an average of 12 months. The clinical progression of kuru is divided into three specific stages, the ambulant, sedentary and terminal stages.
In the first (ambulant) stage, the infected individual may exhibit unsteady stance and gait, decreased muscle control, tremors, difficulty pronouncing words and involuntary head movement. This stage is named the ambulant because the individual is still able to walk around despite symptoms.
In the second (sedentary) stage, the infected individual is incapable of walking without support and suffers severe tremors. Furthermore, the individual shows signs of emotional instability and depression, yet exhibits uncontrolled and sporadic laughter. Despite the other neurological symptoms, tendon reflexes are still intact at this stage of the disease.
In the third and final (terminal) stage, the infected individual’s existing symptoms, like ataxia, progress to the point where they are no longer capable of sitting without support. New symptoms also emerge: the individual develops difficulty swallowing, which can lead to severe malnutrition. They may also become incontinent, lose the ability to speak and become unresponsive to their surroundings, despite maintaining consciousness. Towards the end of the terminal stage patients often develop chronic ulcerated wounds that can be easily infected. An infected person usually dies within three months to two years after the first terminal stage symptoms, often because of pneumonia or infection.
Kuru is largely localised to the Fore people and people with whom they intermarried, and was transmitted through ritualistic cannibalism. The Fore people ritualistically cooked and consumed body parts of their family members following their death to symbolise respect and mourning. Because the brain is the organ enriched in the infectious agent prion, women and children, who consumed brain and viscera, had much higher likelihood of being infected than men, who preferentially consumed muscles.
In 1961, Australian Michael Alpers conducted extensive field studies among the Fore accompanied by anthropologist Shirley Lindenbaum. Their historical research suggested the epidemic may have originated around 1900 from a single individual who lived on the edge of Fore territory and who is thought to have spontaneously developed some form of CJD. Alpers and Lindenbaum’s research conclusively demonstrated that kuru spread easily and rapidly in the Fore people due to their endocannibalistic funeral practices, in which relatives consumed the bodies of the deceased to return the “life force” of the deceased to the hamlet, a Fore societal subunit. Corpses of family members were often buried for days then exhumed once the corpses were infested with maggots at which point the corpse would be dismembered and served with the maggots as a side dish.
The sexual dimorphism evident in the infection rates — kuru was eight to nine times more prevalent in women and children than in men at its peak — is because Fore men considered consuming human flesh to weaken them in times of conflict or battle, while the women and children were more apt to eat the bodies of the deceased, including the brain, where the prion particles were particularly concentrated. Also, the strong possibility exists that it was passed on to women and children more easily because they took on the task of cleaning relatives after death and may have had open sores and cuts on their hands.
Although ingestion of the prion particles can lead to the disease, a high degree of transmission occurred if the prion particles could reach the subcutaneous tissue. With elimination of cannibalism because of Australian colonial law enforcement and the local Christian missionaries’ efforts, Alpers’ research showed that kuru was already declining among the Fore by the mid‑1960s. However, the mean incubation period of the disease is 14 years, and 7 cases were reported with latencies of 40 years or more for those who were most genetically resilient, continuing to appear for several more decades. Sources disagree on whether the last sufferer died in 2005 or 2009.
Initially, the Fore people believed the causes of kuru to be sorcery or witchcraft. Meanwhile, patrol officers believed that kuru could be psychosomatic, or caused by a mental factor. They also thought that the magic causing kuru was contagious. Another theory for what was causing kuru was cassowary disease, also called negi-negi. This disease, the Fore people believed, was caused by ghosts because of the shaking and strange behavior that comes with kuru. To attempt to cure this, they would feed victims pork and casuarinas bark. Prior to the late 1950s, patrol officers thought that kuru was psychosomatic and was caused by the trauma of Western colonization and perpetuated by beliefs in sorcery and witchcraft. It was not until 1957 that cannibalism was investigated with data, by Gajdusek, to be the cause of kuru. However, it was not considered a priority because it was thought to be too strange or evidence that theorised cannibalism as a cause lacked proper evidence. Cannibalism, however, was a reasonable enough explanation for kuru that the Australian administration banned the practice of feasting on the dead, until it was nearly obsolete by 1960. As the number of cases of kuru decreased, those in medical research were able to properly investigate kuru, which then led to the modern proposition of prions being the cause of kuru.
Kuru was first described in official reports by Australian officers patrolling the Eastern Highlands of Papua New Guinea in the early 1950s. Some unofficial accounts place kuru in the region as early as 1910. In 1951, it was Arthur Carey who first used the term ‘kuru’ in his report to describe a new disease afflicting the Fore tribes of Papua New Guinea. In his report, Carey noted that kuru mostly afflicted Fore women, eventually killing them. In 1953, kuru was observed by patrol officer John McArthur who provided a description of the disease in his report. McArthur believed that kuru was merely a psychological episode resulting from the confirmed sorcery practices of the tribal people in the region.
It was not until the time that the Kuru disease had spread into an epidemic when Daniel Carleton Gajdusek, a virologist, and Vincent Zigas, a medical doctor, first started doing research on the disease in 1957. It was first noted in the Fore, Yate and Usurufa people in 1952-1953 by anthropologists Ronald Berndt and Catherine Berndt. After the disease had festered into a bigger epidemic the tribal people called to Charles Pfarr, a Lutheran Medical Officer to come to the area to report the disease to Australian authorities.
In effort to understand the pathology of Kuru disease, Gajdusek established the first experimental tests on chimpanzees for Kuru at the National Institutes of Health (NIH). The methods of the experiment would be to introduce the kuru brain material to the closest human relative, the chimpanzee, and to document the behaviors of the animal until death or a negative outcome would occur. Michael Alpers, an Australian doctor, collaborated with Gajdusek in providing the samples of brain tissues he had taken from an 11-year-old Fore girl who had died of Kuru. In his work he was also the first to document the first bibliography of the Kuru disease. Gajdusek was joined by a man named Joe Gibbs to monitor and record the behavior of the apes and conduct autopsies. Within two years, one of the chimps, Daisy, had developed kuru, demonstrating that the unknown disease factor was transmitted through infected biomaterial and that it was capable of crossing the species barrier to other primates. After confirmation from Elisabeth Beck, this experiment brought about the first conducted transmission of Kuru and was deemed a very important finding in the advancement of human medicine leading to the award of a Nobel Prize in Physiology or Medicine to Daniel Carleton Gajdusek in 1976.
Subsequently, E. J. Field spent large parts of the late 1960s and early 1970s in New Guinea investigating the disease, connecting it to scrapie and multiple sclerosis. He noted similarities in the diseases interactions with glial cells, including the critical observation that the infectious process may depend on structural rearrangement of the host’s molecules. This was an early observation of what was to later become the prion hypothesis.