Known colloquially as ‘mad cow disease’, this is a fatal and untreatable disease. Along with scrapie in sheep and CREUTZFELDT-JACOB DISEASE (CJD) in humans, BSE belongs to a class of unusual degenerative diseases of the brain known as transmissible spongiform encephalopathies. The disease is caused by abnormal PRION proteins, which are resistant to cellular degradation. These abnormal prion proteins accumulate in and eventually cause the death of nerve cells, both in the spinal cord and the brain. The rare human disease CJD occurs throughout the world and is of three types: sporadic, iatrogenic (see IATROGENIC DISEASE) and inherited.
Since the BSE epidemic in cattle developed in the UK in the 1980s, however, a new variant of CJD has been identiﬁed and is believed to be the result of consumption of the meat of BSE-infected cattle. Studies in transgenic mice have conﬁrmed that BSE caused variant CJD. The new variant has aﬀected younger people and may have a shorter incubation period. If this incubation period turns out to be the same as for the other types of CJD, however, it could be 2005– 2010 before the peak of this outbreak is reached. Over 148 people had died, or were dying, from variant CJD in the UK by the year 2005.
The appearance of BSE in cattle is believed to have been caused by a gene mutation (see GENETIC DISORDERS), although whether this mutation ﬁrst occurred in cattle or in some other animal remains uncertain. Although the ﬁrst case of BSE was oﬃcially reported in 1985, the ﬁrst cattle are thought to have been infected in the 1970s. BSE spread to epidemic proportions because cattle were fed meat and bone meal, made from the oﬀal of cattle suﬀering from or incubating the disease. Mother-to-calf transfer is another likely route of transmission, although meat and bone meal in cattle feed were the main cause of the epidemic. The epidemic reached its peak in 1992 when the incidence of newly diagnosed cases in cattle was 37,545.
A two-year UK government inquiry into the BSE epidemic concluded that BSE had caused a ‘harrowing fatal disease in humans’, and criticised oﬃcials for misleading the public over the risk to humans from BSE. Consequently, a compensation package for patients and relatives was made available. Meanwhile, a ban on the export of UK beef and restrictions on the type of meat and products made from beef that can be sold to the public were put in place. Although initially thought to be a problem primarily conﬁned to the UK, several other countries – notably France, Germany, Spain, Switzerland and the United States – have also discovered BSE in their cattle.