This disease occurs exclusively among the Fore linguistic group of natives of the New Guinea highlands and is included here because of its historical interest as the first slow infection caused by an unconventional transmissible agent to be documented in human beings. It was known as “laughing sickness” because of pathological outbursts of laughter that it induced in affected individuals. Clinically the disease takes the form of an afebrile, progressive cerebellar ataxia, with abnormalities of extraocular movements, weakness progressing to immobility, incontinence in the late stages, and death within 3 to 6 months of onset. In some ways it is similar to the ataxic (Brownell-Oppenheimer) variant of CJD. The remarkable epidemiologic and pathologic similarities between kuru and scrapie in sheep were pointed out in 1959 by Hadlow, who suggested that it might be possible to transmit kuru to subhuman primates. This was accomplished in 1966 by Gajdusek and coworkers; inoculation of chimpanzees with brain material from affected humans produced a kuru-like syndrome in chimpanzees after a latency of 18 to 36 months. Since then the disease has been transmitted from one chimpanzee to another and to other primates by using both neural and nonneural tissues. Histologically there is a noninflammatory loss of neurons and spongiform change throughout the brain, but predominantly in the cerebellar cortex, with astroglial proliferation and periodic acid-Schiff–positive stellate plaques of amyloid-like material (“kuru plaques”). The transmissible agent has not been visualized, however.
Kuru has gradually disappeared because of the cessation of ritual cannibalism by which the disease had been transmitted. In this ritual, infected brain tissue was ingested and rubbed over the body of the victim’s kin (women and young children of either sex), permitting absorption of the infective agent through conjunctivae, mucous membranes, and abrasions in the skin.
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