I CAN help Professor Stanley Prusiner understand why such a small number of people have developed new variant CJD (v-CJD) "while 10 million others with the same environmental history had not" ("Nobel winner challenges CJD link to beef", 7 June). "These people didn't go out and crave cow brains," he says. But we did all swallow infected cow brains, because until November 1989 they were routinely added to meat products. Fortunately only about 30 per cent of people are susceptible to CJD and even they have to swallow a large dose of the agent. Prusiner is also mystified by the vic- tims' youth. The 26 cases of v-CJD are so young because, being children between 1981 and 1989, they were shedding teeth which provided raw areas in their mouths for the agent to enter directly into the blood stream. This shortens the incubation period of CJD.
The evidence that v-CJD is caused by BSE is partly epidemiological: the UK is the only country that has had to destroy nearly 300,000 BSE- infected cattle (Switzerland has the next highest incidence - 300 cattle destroyed) and the UK is the only country that has had 26 v-CJD deaths.
HC Grant, MD, FRCP