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Educating the Veterinary Students of Tomorrow

BSE

Compassion in World Farming, 2018

Mayo Clinic, 2018



Bovine Spongiform Encephalopathy (BSE) or ‘Mad Cow Disease’ as it is more

commonly known, is a degenerative neurological disease of cattle which leads

to severe and fatal neurological signs (WHO, 2018). It belongs to a family of

Transmissible Spongiform Encephalopathies (TSEs) which cause a variety of

neurodegenerative diseases in humans and animal for example; Scrapie in

sheep and Creutzfeldt-Jakob disease (CJD) in people. The first case of BSE in

the UK was discovered in December 1984 in Sussex. The cow in question presented with clinical signs of an arched back and weight loss. This eventually progressed to head tremors, convulsions and death.


After a Post Mortem, BSE was confirmed. By this stage other cows in the herd and on other farms had started to show similar signs. This prompted the government to set up a scientific team to investigate BSE and any implications it could have on Public Health (Ainsworth et al, 2000). Of the approximate 200,000 cases of BSE that have been diagnosed in cattle, 97% were reported from the UK. At the peak of the UK outbreak in 1992, 37,280 cases were reported in a single year (MSD Vet Manual, 2018). In 1996, scientists discovered a new strain of CJD in people that they believed was caused by exposure to BSE through the consumption of contaminated meat (FSA, 2005). This prompted a huge drive to understand and control BSE.

After much debate, it was decided that the most likely cause of BSE

is a proteinaceous infectious particle called a prion (MSD Vet

Manual, 2018). Prions cause abnormal folding of proteins and

protein aggregation. They are resistant to heat, freezing, UV light

and disinfectants. Two types of BSE have been described-Atypical

and Classic. Classic BSE is the most common form and is caused by

transmission of these prions-it is an infectious disease.  The main

method of transmission of BSE is the ingestion of contaminated

animal proteins (Meat and Bone Meal) (MSD Vet Manual, 2018). The

pathogenesis for    infectious transmission is unknown but the current hypothesis is that after oral exposure the infectious proteins replicates in the Peyer’s patches of the ileum. They then migrate via peripheral nerves to the Central Nervous System (CNS). Atypical BSE occurs spontaneously and as a result, researchers believe that this was the original source of BSE in the UK. The incubation period of BSE is around 2 to 8 years. Most animals develop clinical signs around 3 to 6 years old (MSD Vet Manual, 2018).

Clinical signs of BSE can vary from very subtle neurological signs to begin with for example; behavioural changes. These can then progress to more severe signs for example; tremors, ataxia and hypermetria. There is no definitive way to diagnose BSE apart from euthanasia and submitting the carcase for further histopathology of the brain and spinal tissue. BSE is a notifiable disease and any suspicions should be reported to the Animal Plant and Health Agency (APHA). Whilst the animal in question is being tested for BSE, a movement restriction is placed on the farm until a definitive diagnosis has been made (GOV.UK, 2018). Any cows born in the same herd as the BSE case up to a year before or after its birth or cows that were reared with a BSE case at any time before both were up to a year old, are identified, culled and tested. Any offspring of female cows that test positive for BSE are culled as well. Farmers receive compensation for any cows that are culled.

In order to prevent the spread of BSE, a ban was put in place in the UK in August 1996 that prohibited the feeding of any kind of animal protein to farm animals (FSA, 2005). This ban came into force in the rest of the EU in 2001. In order to protect Public Health, it is compulsory to test cattle that are slaughtered for human consumption if they are over 30 months of age or if they were born in Romania, Bulgaria, Croatia or any non-EU country. Cattle over 48 months that were born in the EU/cattle over 24 months if born outside of the EU must also be tested for BSE if they were sent for emergency slaughter or were found dead ie. fallen stock. Fallen stock must be sent to an approved BSE sampling site (GOV.UK, 2018). Further preventative measures include removal and disposal of Specified Risk Material (SRM) eg; brain and spinal cord, in a safe manner in the slaughterhouse in order to decrease the risk of these infectious prions entering the food chain. Also all body parts of cattle born in the UK before 1 August 1996 are SRM and are banned from entering the food chain. As a result of these measures, no cases of BSE were reported in 2016, with Northern Ireland achieving BSE negligible risk in May 2017 (DAERA-NI, 2017).

References:

Ainsworth, C., Carrington, D. (2000). ‘BSE disaster: the history’. New Scientist. Available at: https://www.newscientist.com/article/dn91-bse-disaster-the-history/ (Accessed: 8th February 2018)

Compassion in World Farming (2018) Available at: https://www.ciwf.org.uk/farm-animals/cows/dairy-cows/ (Accessed: 11th February 2018)

DAERA (2018) Available at: https://www.daera-ni.gov.uk/news/northern-ireland-achieves-bse-negligible-risk-status (Accessed: 8th February 2018)

Drink-Milk.com (2018) Available at: https://www.drink-milk.com/breeds-of-dairy-cattle/ (Accessed: 11th February 2018)

Food Standards Agency (2005) BSE and Beef New Controls Explained

GOV.UK (2018) Available at: https://www.gov.uk/guidance/bse (Accessed: 8th February 2018)

Mayo Clinic (2018) Available at: https://www.mayoclinic.org/diseases-conditions/creutzfeldt-jakob-disease/multimedia/normal-and-diseased-prions/img-20007478 (Accessed: 11th February 2018)

MSD Veterinary Manual (2018) Available at: http://www.msdvetmanual.com/nervous-system/bovine-spongiform-encephalopathy/overview-of-bovine-spongiform-encephalopathy (Accessed: 8th February 2018)

WHO (2018) Available at: http://www.who.int/zoonoses/diseases/bse/en/  (Accessed: 8th February 2018)