Bovine Spongiform Encephalopathy is a
degenerative brain disorder of cattle known more commonly as
Mad Cow Disease. It is part of a family of diseases known as
Transmissible Spongiform Encephalopathies, or
TSE's. It was
supposedly first discovered in
November 1986 in the
UK and by the following
October, more than 169,472 cases had been identified. Other
sporadic cases were soon identified in countries such as
France,
Portugal,
Germany and
Ireland. The occurrence of
BSE in the
United States or any other
major milk producing country outside the
European Union has not been officially confirmed.
BSE causes small holes to form in the tissue of the brain, giving it a sponge-like texture. Similar spongiform diseases such as CJD (Creutzfeldt-Jakob disease) have been identified in humans since the 1920s and scrapies has been existent in sheep for around 250 years. Cattle that are infected with BSE begin to show signs after around 5-10 years of life; so infected cattle may not be identified until the disease has already been passed on. In fact, depending on the life of the cattle, the disease may not be identified at all. It is believed that the build up of an abnormal protein called a prion is the cause of BSE, leaving holes in the brain causing serious neurological impairments and eventually death. BSE can only be diagnosed by inspecting the brain, hence BSE can only be diagnosed once the animal is dead.
Symptoms include apprehensiveness, nervousness, reluctance to cross concrete, turn corners, enter yards, go through doorways or permit milking, occasional aggression directed at other cattle or humans, manic kicking when milked, head shyness with head held low, high stepping gait particularly with hind legs, difficulties in rising, skin tremors, loss of weight or the ability to yield milk.
BSE is usually transferred from cow to cow via their feed, which used to be made from recycled parts of carcasses from infected cows. These parts of dead cows were fed back to cows as a protein supplement and thus passed on the disease. It was originally thought that BSE developed after scrapie infected sheep parts were included in the cattle feed and thus its spread was sped up by the consumption of recycled brain tissue from cows that had themselves become infected. However, Ministry of Agriculture researchers have not rejected the scrapie link claiming changes in the abattoir by-product treatment meant that processed tissue was no longer exposed to certain chemicals or high temperatures which killed the BSE prion. Scientists are yet to prove other forms of transmission including maternal transmission via milk, blood or amniotic fluid. Some scientists claim that there may be some degree of maternal transmission but there is also evidence that cattle can inherit a genetic susceptibility.
The central nervous system consists of the brain and spinal cord, both of which play a huge part in the receiving and directing of nerve signals around the body via the peripheral nervous system. When the brain is infected with BSE, its functions are severely impaired and thus the cow's behaviour is abnormal. Although BSE has no direct affect on the spinal cord, it is still infected and can still pass on the disease to another cow if consumed. A normal unaffected cow will have none of the symptoms of BSE, it will be able to co-ordinately walk around corners and through doors, stand up and down cross concrete and yield milk. Once the cow has been infected with BSE, even these simple functions become almost impossible for the cow or it seems reluctant to complete the task.
After the disease was discovered in 1986, tests were run to find the cause and method of transmission of the disease. After months of study, a hypothesis was announced that bone meal and meat in cow feed was the only plausible cause of BSE. Requests were sent out to several compounders asking for details on the cow feed including how much bone meal and meat was included etc. The results added plenty of back up for the hypothesis, and in 1988, BSE became an official disease with the transmission declared being via cow feed. As soon as BSE was known to be transmitted via cow carcasses in cow feed, a total ban was put on the feeding of recycled animal tissues to cattle and other animals. This was a large success and estimations were made that the disease would be eliminated by 1999, but these have been rethought due to the unsatisfactory handling of Specified Risk Materials (SRM), which are organs identified as possible carriers. Certain SRM's include the brain, spinal column, spleen, thymus, tonsils, and intestines.
Soon enough, humans became concerned that BSE could be transmitted to humans via beef products. Although several scientists claimed that there was no chance it could pass on to humans, people were still concerned. In late 1988, the beef consumption rate dropped slightly due to the BSE scare, but in 1990 it dropped by almost 30% due to a newspaper article on a cat which had caught a form of Feline Spongiform Encephalopathy. After only two weeks the consumption level had recovered to 95% that of what it was before the scare.
In 1995, the UK beef industry had another scare after newspaper reports linked BSE with the contraction of CJD and supermarket sales immediately dropped by 18%. In March 1996, BSE became a worldwide issue. This followed the UK Minister of Health announcing the discovery of a new strand of CJD, which became known as nvCJD (New Variant Creutzfeldt-Jakob disease). The announcement lead to the speculation that cows and their beef products could in fact infect humans with BSE. Only 7 days after that there was a total ban on the export of UK beef. On May 3 1996, a slaughter program began that would lay waste to any cow that was over 30 months old at the time. By December 1,643,057 retired beef and dairy breeding cows and 337,586 prime beef animals over 30 months old had been destroyed at an estimated cost of £1 billion, or roughly £1,000 a head. This project is expected to continue until all breeding animals born before August 1st 1996 are destroyed at the end of their working lives. By the end of 1997, around 12,000 beef breeding animals were being killed a week.
In the midst of all this, the UK was still trying to lift the ban on its beef. To show its co-operation, the UK culled a further 50,000 more adult cows which were identified as most likely to be carrying BSE and 14,000 more cows which were the offspring of BSE infected cows. They did this in return for permission to export beef from cattle born after August 1 1996, when the SRM became an illegal substance and there was no further risk of BSE being transmitted.
After the beef ban, consumption of beef rose to about 80% of normal levels, except for processed meat such as beef burgers which took a little longer to recover.
These are the precautions that the UK and other infected countries have taken out to attempt to destroy the outbreak of BSE again. If everything continues on as it has been the past few years, they estimate that BSE will be extinct by 2005. Because of this, there aren't many future developments needed to aid in the destruction of BSE. Instead, scientists should start to look at nvCJD, even though only 1 in 1,000,000,000 people will catch it.
References cited:
http://www.hc-sc.gc.ca/pphb-dgspsp/tmp-pmv/2001/bse_e.html
http://www.defra.gov.uk/animalh/bse/chronol.pdf
http://www.defra.gov.uk/animalh/bse