Kuru with incubation periods exceeding two decades.

The clinical characteristics of kuru in 15 patients are described. All the patients had a history of joint pains preceding difficulty walking. The severity of the neurological dysfunction varied from mild truncal and limb ataxia necessitating the use of a stick for walking to terminal illness accompanied by marked ataxia, rigidity, spasticity, and dementia. All the patients with kuru in this study had a apprehensive, frightened facial expression. Most of the patients examined showed diminished or absent optokinetic nystagmus bilaterally. Apprehensive facies and diminished optokinetic nystagmus have not previously been described in kuru. The other clinical features of the current patients with kuru are similar to those recorded twenty years ago. Epidemiological surveillance, anamnesis, and missionary reports strongly suggest that all the patients described in this study were exposed to the kuru agent more than two decades ago through ritualistic cannibalism. Thus the incubation period or time interval from exposure to the onset of clinical illness exceeds two decades, while the duration of illness is two years or less. The cause of these extraordinarily long incubation periods is unknown but may result in part from exposure to small doses of the kuru agent through an inefficient oral route.