Kuru is a disease that decimated a number of small groups of people living in the remote highland jungles of Papua New Guinea in the early to mid twentieth century; most famous of those groups in anthropological circles are the Fore. Though kuru was known and studied, the origins and mode of transmission of the fatal disease were a mystery to the Fore and westerners alike for many years.
The Fore were accustomed to holding elaborate mortuary feasts to commemorate the death of a relative. During the feast, the body of the deceased was dissected, cooked and then consumed. The men, seemingly eager in every culture to assert their status and take the best, would eat the muscles - the meat - themselves; the women and children consumed the brains and other offal. Though this probably strikes you as bizarre in the extreme, to the Fore this was a respectful celebration of the life and passing of a loved one, and all the relatives participated in the loving dissection of the corpse.
However, one member of this rather small and closed society - a group of intermarrying villages totally perhaps 1500 people in all - developed a condition whereby they began to tremble and shake and walk funny, and eventually died. At first just one person had it; their passing was celebrated in the customary manner, and soon many others began to die of the same condition. The disease, which the Fore called kuru, "the trembling sickness", begin with shaking; the infected individual might begin to laugh uncontrollably, and would gradually deteriorate - over a period of between three months and three years - until the person, unable to walk, talk, or eat, finally died, a frozen smile on their paralyzed face. By the late 1950s, the disease was killing some 200 Fore a year, four times as many women as men. There was real concern that the Fore would die out, but the illness itself was still a mystery.
Westerners, who only reached the New Guinea highlands in the mid-twentieth century, and colonized it a little later, were disgusted by the cannibalism (and head-hunting, but that's another node) so popular among the many ethnic groups of the area, and outlawed it. Soon the incidence of kuru began to decline. American pediatrician and virologist Daniel Carleton Gajdusek lived among the Fore in the 1960s and set to work trying to find out what was causing this unusual localized disease. Gajdusek took samples of the brains of some people who had died of kuru, and, back in the States, mashed it up and injected into the brains of poor laboratory chimpanzees; after two years they developed kuru. The scientific community was rocked on hearing of this proof that diseases could incubate for such a long period of time; cross-species infection was also a shocker. Gajdusek and his colleague Baruch S. Blumberg won a Nobel Prize for their work on these types of diseases.
Among the Fore, kuru was transmitted by cannibalism; women and children were at greatest risk of contraction as they consumed the most contaminated parts, the brains and nervous system. Scientists now conjecture that kuru among the Fore was caused by a spontaneous mutation in one individual who around 1915 developed a random case of spongiform encephalitis (related to Creutzfeldt-Jakob Disease) as a result. It is also now hypothesized that an infectious agent called a prion is responsible for the spread of diseases such as this.
Kuru was in the news again in the 1990s because of another form of spongiform encephalitis, this one bovine: mad cow disease. (There's one in sheep too, scrapie.) Cows contracted the condition from being fed the ground-up body parts of infected cows; infected cows, just like infected Fore, died after their brains turned all spongy. A few humans who ate contaminated beef developed a variant form of CJD, which is kind of scary: cross-species contamination again. But even more frightening is that scientists don't really know how long an incubation period the various forms of this disease have. Though no Fore born after 1959, when cannibalism was outlawed, has developed kuru, some middle-aged individuals who took part in mortuary feasts as children are only now showing signs of kuru; could something similar happen with CJD? Medical researcher Michael Alpers, who lived in New Guinea among the Fore for many years, conjectures that it might. He points out that as the agents and mode of transmission are essentially the same between the two diseases, other factors may be similar as well. Ewwww.