Letter: Confusion about sources of BSE

Sir: The widespread confusion about BSE, scrapie and CJD is due to the fact that the transmissible spongiform encephalopathies (TSEs) - CJD, BSE, scrapie and kuru - are caused by a mysterious infective agent (the scrapie agent) which is poorly understood even by scientists. Thus we read (report, 24 July) that, "if sheep are infected with BSE the disease can be transmitted from mother to offspring - which has not been proved to happen in cattle." But scrapie is maternally transmitted (lambs are infected in utero), which is why it has been with us for centuries.

When our cattle were forced before July 1988 to swallow dead sheep (all of whose brains were still inside the skulls and therefore, unlike cattle brains, not in our food chain) our bovine friends caught the ovine TSE, scrapie, now renamed BSE. And there is plenty of evidence that BSE is also maternally transmitted, but the Ministry of Agriculture, Fisheries and Food is denying this. Thus it proclaims that calves are infected because farmers have been continuing to feed the infected material, banned since 1988.

The reason why "scrapie is not believed to pose any risk to humans" is that abattoir workers do not routinely remove sheep's brains - the infective organ - from the skulls (not worthwhile) so that, unlike cattle brains until 1989, they never finish up in our "meat products". They finish up in animal feed instead. Sheep's spinal cords, however, still arrive on our dinner plates, in lamb chops, and I have no doubt that is where genetically susceptible humans have hitherto been catching CJD. The proposed new ban which includes sheep spinal cords is therefore welcome.



London NW3