Abstract
Bovine spongiform encephalopathy (BSE) is a neurological disorder which has affected cattle in the UK. It has been suggested that it is caused by prions and these may also be responsible for scrapie in sheep and Creutzfeldt-Jakob disease (CJD) in humans. The molecular mimicry theory is an alternative model which suggests that BSE could be an autoimmune disease caused by exposure of cattle to bacteria showing cross-reactivity with nervous tissue. Acinetobacter calcoaceticus , Ruminococcus albus , Agrobacterium tumefaciens and Escherichia coli have been shown to contain molecular sequences which resemble brain tissue. Neurological damage is caused either by prions or by autoimmune mechanisms and the contrasting features of these two theories are reviewed. Furthermore, the autoimmune theory implies that there is no need for a cull of cattle, and that humans will not develop CJD provided they are not exposed to these bacteria.