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Kuru Revisited

New evidence from the waning kuru epidemic suggests that incubation periods for prion diseases are surprisingly long — and that more surprises are likely.

Kuru was the first transmissible spongiform encephalopathy (prion disease) discovered in humans. Transmission between humans was by ritual endocannibalism (consumption of deceased relatives, primarily by women and children). A minimum incubation period of about 5 years has been estimated from childhood cases. In this study, the authors investigated the maximum incubation periods of kuru by conducting surveillance for new kuru diagnoses in the Fore region of Papua New Guinea from July 1996 through June 2004.

Only 11 patients with kuru were identified, and none had onset in the last 3 years of the study. Because endocannibalism had evidently ceased by 1960, the authors estimated that the incubation periods in these patients ranged from at least 34 to 41 years and may have exceeded 50 years in some patients. Genetic testing in the 11 patients showed that most of these recently diagnosed patients with kuru (i.e., with long incubation periods) were heterozygous at codon 129 of the prion protein gene.

Comment: I was in New Guinea as a consultant to the Papua New Guinea Health Council in 1964, when hundreds of young women and children were dying each year and when the shocking evidence of transmission by cannibalism was first being gathered. For me, this article closes the saga of this nightmarish epidemic. Collinge and colleagues, however, focus their discussion on a darker implication of these findings. The epidemic of variant Creutzfeldt-Jakob disease (vCJD) in the U.K. similarly appears to be abating, after more than 160 human cases putatively acquired from products contaminated with the prions of bovine spongiform encephalopathy. Yet all patients with vCJD tested have been homozygous for methionine at codon 129, a polymorphism site known to influence susceptibility to prion diseases and length of incubation period. As the authors suggest, because most patients with kuru in this study were heterozygous at codon 129, a new wave of cases of vCJD in heterozygotes may be coming.

Beware predictions about prion diseases. The idea that some late-life degenerative diseases could be transmissible once seemed absurd; the idea that human cannibalism might lead to epidemic disease was unthinkable. Transmission of disease to children by injecting growth hormone derived from human pituitaries was unimaginable. Surely, it was thought, the rendering industry (the pioneers of recycling) could not be critical in the catastrophic epidemic of "mad cow disease," and we were confidently assured that the cattle disease could not be transmitted to humans. Kuru does appear to be gone, but the next twist in the prion story will probably be a surprise.

— Richard T. Johnson, MD

Dr. Johnson is Professor of Neurology, Microbiology, and Neuroscience, The Johns Hopkins Medical Institutions and The Johns Hopkins Hospital, Baltimore, MD.

Published in Journal Watch Neurology September 5, 2006

Citation(s):

Collinge J et al. Kuru in the 21st century — an acquired human prion disease with very long incubation periods. Lancet 2006 Jun 24; 367:2068-74.

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