Most cases of BSE have been in older dairy cows and almost all of the infective material is concentrated in the brain, spinal cord, spleen, tonsils and other so-called specified bovine offal (SBO). This means that steaks and joints of muscle meat from young beef cattle have always been an unlikely source of infection. Cheap meat products made from ground up meat and offal, including brains, of older dairy cows were much riskier.
In 1989 it was ordered that all SBO should be removed from cattle at slaughter and incinerated and from 1996-2005 it was illegal to sell meat from cattle more than 30 months old unless they came from animals guaranteed to be solely grass fed. These were important protective measures especially the rule about SBO but nature probably also played its part. It is usually difficult for diseases to pass between species and in this case cow prion is quite different from its human equivalent. This means that cow prion is much less effective at causing shape change in human brain protein than with cattle brain protein.
Next Dr Geoff looks at the wider impact of BSE