Neuropathology and the scrapie-kuru connection.

When their kinship was surmised 35 years ago, scrapie and kuru were linked mainly by their neuropathologic similarity. Most notable were neuronal degeneration and intense astrocytosis with little, if any, inflammation. Especially eye-catching in kuru were the vacuolated neurons--the histologic hall-mark of scrapie that drew me to the human disease from the start. Because spongiform change in gray matter neuropil is variable and usually lacks prominence in both scrapie and kuru, it was not part of the resemblance I saw in them. Amyloid plaques, so characteristic of kuru, also did not figure in the similarity, for they had not yet been reported in scrapie. Despite the uncertainty at the time about the pathologic essence of scrapie, the two diseases still looked alike. Their eventual connection--however tenuously held together initially by the few likenesses--has survived as a tribute to morphologic observation. It provided the essential link that helped ensure the kinship a lasting place in comparative neuropathology.