Old headaches for the cattle industry dating back to the 1990’s returned with a vengeance in the last few months at an unnamed farm in Aberdeenshire.
An investigation is under way into the “isolated” case of bovine spongiform encephalopathy, the first in Scotland in over a decade and the latest of 17 outbreaks in the wider UK area since 2011 (the last one reported in Wales in 2015). A 5-year old member of a beef herd was diagnosed with the ‘mad cow disease’ before it and 4 others were destroyed and a movement ban on the farm was imposed by the Scottish government. While these measures may seem to be grossly overcompensating at first glance, they are a far cry from the 4.4 million cattle slaughtered as a preventative measure during the last major outbreak in the early 1990’s, in which at least 100,000 animals were infected and 17 people died by contracting variant Creutzfeldt-Jakob Disease (vCJD), the human version of BSE. The effects of the 1990’s outbreak continue to affect cattle production and food safety legislation to this day, not just in the UK but in France, Japan and the U.S as well. So what exactly is mad cow disease and what makes it so deadly?
Bovine spongiform encephalopathy, as the disease is formally known, is defined as a neurodegenerative disease that primarily affects and deteriorates the brain and spinal cord. The BSE name shows how it is classified: bovine (affects cattle), spongiform (from the ‘holes’ in the brain that affected livestock display post-mortem) and encephalopathy (literally “disorder of the brain”). The exact cause of the disorder is still unknown, but is widely theorised to be caused by a class of misfolded proteins called prions which replicate exponentially in the brain, so the alpha helices and beta sheets which form the basis of all protein structures are fatally twisted and merged together. The damage to the brain tissue as the cells die off subsequently gives rise to hyper-responsiveness, tremors and abnormal posture in cows, which are the defining features of the disorder. Afflicted cattle later enter a coma and then die within months. A cure for BSE has unfortunately not been discovered as of yet; the only viable treatment is usually palliative care. Furthermore, because it has a very long incubation period of up to 8 years, (i.e. the timespan from when the cattle are infected to when the symptoms first manifest) any treatment would most likely begin too late to make any difference.
Another potentially disastrous consequence of BSE is that it can also be contracted by humans as variant Creutzfeldt-Jakob Disease when eating beef from cattle that has been infected; the agent is not destroyed even when the meat is cooked or treated. Like BSE, this primarily affects the brain and is often diagnosed when affected individuals show symptoms of dementia, poor motor control or anything else that indicates a neurological dysfunction.
The life expectancy in humans once infected is 13 months at most, with palliative care again usually being the only treatment available. vCJD has killed at least 177 people in the UK since the first outbreak in 1986, which also saw domestic sales of beef fall by 40% as household consumption dropped by a quarter on the previous year. Overseas exports were also crippled by an EU ban that was only lifted in 2006; the overall cost to the UK economy was at least £740 million. In addition, individuals who spent at least 6 months living in the UK from 1980 to 1996 can be barred from donating blood in the USA, Canada, New Zealand and some EU member states. This is due to the presence of prions in the blood of affected individuals and evidence that vCJD can be transmitted between humans via blood transfusion. This is similar to the transmission of kuru, a virtually identical disease exclusive to the Fore tribe of Papua New Guinea, due to their traditions of intermarrying and ritualistic cannibalism of recently deceased (infected) family members. The epidemic declined rapidly after the Fore discarded cannibalism, lending further evidence to the theory of vCJD transmission. What is more unclear, however, is whether the disease can be sexually transmitted. While there is no evidence for this theory the U.S. federal government has still banned import of any donor sperm for use in IVF treatment, ostensibly to prevent another outbreak, which has led to the loss of the very popular Scandinavian sperm imports.
BSE is transmitted in a similar manner between cattle; the outbreak in the UK is believed to have started with lax health and safety regulations that led to cattle being fed meat and bone meal (MBM) containing the infected remains of other cattle. An investigation into the outbreak, after the election of the New Labour government in 1997, led to a ban on feeding MBM to cattle which in turn led to a sharp reduction in the number of cases of BSE in the UK, Europe and North America. In countries that have yet to experience an outbreak, such as South Korea, preventative measures are carried out through import control, feeding regulations, and surveillance.
It is fair to say that nowadays, the threat of BSE has been greatly reduced from where it was from the 1980’s and 90’s. The effects of the outbreak across the world resulted in a new era of food safety and cattle regulations for Europe and North America, and cemented the outbreak of bovine spongiform encephalopathy as one of the most notable food scandals of all time.