Isolated case of 'Mad Cow Disease' sparks concern

II  JAN 21 2017

Duncan Shrewsbury

An isolated case of 1 cow in Ireland has been reported in the media as heralding the return of ‘mad cow disease’ to the UK [1]. It has been confirmed that the cow died from a spontaneous (‘atypical’) form of the disease, rather than the transmitted form [2].

What is Mad Cow Disease?

In the late 1980s there was an epidemic of cows falling ill, and dying spontaneously. They developed weakness, and lost the ability to stand [3]. More dairy cattle were affected. Through epidemiological case studies, it was discovered that these cows were fed on a type of feed that derived from animal products.

High intensity farming requires that cattle be fed a diet high in protein, calories and minerals, such as calcium. Cattle feed supplemented with scrap meat and bones from other animals was believed to have become contaminated with tissue from the brain and spinal cord of diseased slaughtered sheep. Through this route, prions (an abnormal, disease-causing protein) entered the food chain [3, 4].

Diseases caused by this type of prion affect the central nervous system (brain and spinal cord) and cause gradual degeneration. The prions predominantly remain in the nervous tissue, but through cross-contamination in slaughtering and meat preparation processes, can come into contact with, and spread to, meat that enters the human food chain.

In humans, these prions can cause variant Crutzfeldt-Jakob Disease (‘vCJD’). What caused a challenge to establishing the cause, was the long delay between ‘infection’ and illness from the disease (sometimes more than 10 years). There is no known, effective treatment and the course of the disease in humans can be unpredictable, ultimately resulting in death [4, 5]. The condition, however, is incredibly rare [4].

What are the risks to us now?

There have been no new cases of ‘mad cow disease’ affecting humans for at least 2 years. A total of 177 people were believed to have died from vCJD, the peak of this scare being in the 1990s. Restrictions on animal feeds and meat preparation processes are far tighter [5, 6]. Regular surveillance is performed on livestock to monitor for a variety of disease.

Out of the various different diseases that can affect the brain, transmissible forms of them (e.g. vCJD) are incredibly rare. New standards and regulations in animal welfare, and food production are considered robust and safe [7]. The type of illness that the case reported in the media was not the same as the form of prion disease that was transmitted in the food chain. The cow that was affected was not from a livestock (meat or dairy) herd. Therefore, this incident is not likely to represent a threat. There are, of course, historical risks that remain, and so there is a small chance that we haven’t seen the last of vCJD yet.

Any opinions above are the author's alone and may not represent those of the NHS or Mind and Medicine. Any comment is based on the best available evidence at the time of writing. All data is based on externally validated studies unless expressed otherwise. Novel data is representative of sample surveyed. Online recommendation is no substitute for seeing your own doctor and should not be taken as medical advice.

References
[1] Parsons J. (2017) The return of mad cow disease? 18-year-old cow confirmed dead from BSE. The Mirror, 18th Jan. 2017: http://www.mirror.co.uk/science/return-mad-cow-disease-18-9647025

[2] News Desk. (2017) Ireland reports atypical BSE case in ‘fallen cow’. January 19th 2017: http://outbreaknewstoday.com/ireland-reports-atypical-bse-case-fallen-cow-83874/
[3] Food Safety Research Information Office. (2007) Pathogens and contaminants: a focus on bovine spongiform encephalopathy: https://web.archive.org/web/20080303135425/http://fsrio.nal.usda.gov/document_fsheet.php?product_id=169

[4] Trevett CR, and Singh PN. (2003) Variant Cruetzfeldt-Jokob disease: pathology, epidemiology, and public health implications. American Journal of Clinical Nutrition, 78(3): 6515-6565.

[5] National Institute of Neurological Disorders and Stroke. (2003) Information page: CJD: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Creutzfeldt-Jakob-Disease-Fact-Sheet

[6] NHS Choices. (2015). CJD: http://www.nhs.uk/conditions/Creutzfeldt-Jakob-disease/Pages/Introduction.aspx

[7] Public Health England. (2015) Public health action following a report of a new case of CJD or a person at increased risk of CJD. Crown Copyright: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/474338/CJD_public_health_action_new_case_301015.pdf