Letter: Risk of scrapie infecting humans

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Sir: In her letter ('Primates in peril', 14 May) Helen Grant points out correctly the potential for the spongiform encephalopathies to cross from one species to another. She also estimates correctly the incubation period to be about 20 years. However, scrapie ('sheep BSE') was around at least 200 years ago and, therefore, if man was really at risk, the first case of the human form of the disease should have occurred about 1814. But it didn't.

Yours faithfully,


Hambleton, Lancashire

16 May