The year is 1984, in Sussex, UK. On a cattle farm, Cow 133 is exhibiting weird behavior, acting excessively nervous, and getting violent with farmers and other livestock. What’s more, the cow is also exhibiting loss of coordination, with severe tremors, trouble walking, and getting up from lying down.


A year later, Cow 133 dies suddenly. Not too long after, other cattle on the farm began exhibiting similar symptoms that this animal was showing prior. No one yet knows, but this would become the locus of an outbreak that would go on to have global ramifications.

Over the next half-decade, more and more cattle across the British Isles would demonstrate a similar pathology. The cause? A newfound neurodegenerative disease called Bovine spongiform encephalopathy (BSE), otherwise known as Mad Cow’s disease.

Despite these alarming symptoms, studies from the time–around 1989–lead British experts to think it was unlikely that BSE could pose any risk to humans… Unfortunately, in another 5 years, this was shown to have been a catastrophically incorrect assessment.

On the 21st of May 1995, the 19-year old Stephen Churchill would become the first human to die from variant Creutzfeldt-Jakob's disease (vCJD), the human equivalent of BSE in humans, acquired from the consumption of tainted British beef.


Over the next decade, we would see a massive spread of the diseases and corresponding policies attempting to slow it–including banning British beef exports and culling millions of cattle across the country and the globe. First, BSE and vCJD are detected in neighboring EU countries. Then, in 2000, BSE was detected in Thailand, the first case seen outside of Europe. By 2003, every continent except Oceania had detected cases of neurodegenerative illnesses.

Luckily, by the end of this pandemic, “only” 232 people had perished at the hands of vCJD. What’s horrifying from that figure, however, is that only 232 people had contracted the illness worldwide. There was to be–and there still are–no treatment, no cure, and no recovery. What’s more, testing across the British isles demonstrated that 1 in 2000 British persons have the abnormal proteins that are markers for the disease, labeling them as potential asymptomatic carriers of the deadly neurodegenerative condition.

It is for this reason that anyone having lived in the UK anytime between 1980 and 1996 cannot donate blood in either Canada, Australia, or the US. In almost 2% of the cases in the UK, vCJD was contracted from a blood transfusion, demonstrating that there is always an underlying risk that such transmission could lead to a resurgence in vCJD across the global population.

Seeing all of this, one must wonder what exactly led BSE to be so transmissible and vCJD so deadly? In other words, what is the mechanism of action of these respective diseases?

Well, they are both what’s known as prion diseases. In short, prion disease is caused by a single protein being abnormally misfolded thus, disrupting the proper structure, and said function of the macromolecule. This slight “glitch” in the biological system is no small thing; that one misshapen component somehow induces surrounding proteins to similarly misfold, which causes more proteins to misfold, etc. This was a truly surprising development, as never before had this behavior been observed. Before their discovery, it was thought that all infectious agents needed some form of delivery of genetic material (such as DNA or RNA seen in viruses and bacteria) to influence their victim/host.

Overall, this compounding dysfunction eventually leads to these neurodegenerative diseases we observe in all animals, which can cause the brain to look like swiss-cheese by clumping with other prion groups and forming holes in the brain of the afflicted.

In respect to transmission, it’s pretty simple; consumption of bodily tissue of the afflicted is what can cause intra- & interspecific transmission. In other words, transmission in cows was due to the UK farmers’ desire to save money & reduce waste by “re-using” non-consumed cow remains and organs by feeding them to the other cattle as a cheap and easy source of calories for the livestock. As for humans, eating any BSE-infected products–namely UK beef produced between 1980-1996–was a potential vector for transmission which could have led to developing vCJD.

Now, you may be wondering, what’s the significance of this today? Feeding cattle other cattle remains were outlawed; BSE was all but eradicated globally and only a couple of hundred people internationally were even afflicted. What’s more, prion disease transmissions are extremely limited–in that, definitionally, it is not contagious and can’t yet manage airborne transmission; so what’s the deal?

Well, if the past year has shown us anything, it’s that we need to be ready for unlikely events such as these. While the death toll to date may only be in the hundreds, all it takes is a slight mutation to lead to a global pandemic that kills millions.

What’s more, prion diseases seem to be becoming more and more prevalent every day–namely through Parkinson’s disease, as well as Alzheimer’s disease, which new studies are demonstrating may also be part of this group.

By finally understanding the mechanism of action of any of these diseases–with BSE or vCJD being as good candidates as any–we could help elucidate the unfolding of all prion diseases, and perhaps even unlock some cure or treatment soon.

Works Cited

CDC. “Prion Diseases.” Centers for Disease Control and Prevention, 2019, www.cdc.gov/prions/index.html.

“Creutzfeldt-Jakob Disease.” Alzheimer’s Disease and Dementia, 2019, www.alz.org/alzheimers-dementia/what-is-dementia/types-of-dementia/creutzfeldt-jakob-disease.

“How BSE Crisis Shook Our Faith in Food.” BBC News, 18 Oct. 2018, www.bbc.com/news/uk-45906585.

Medicine, Center for Veterinary. “All about BSE (Mad Cow Disease).” FDA, 23 July 2020, www.fda.gov/animal-veterinary/animal-health-literacy/all-about-bse-mad-cow-disease#:~:text=Can%20People%20Get%20BSE%3F. Accessed 17 July 2021.

Nathanson, N., et al. “Bovine Spongiform Encephalopathy (BSE): Causes and Consequences of a Common Source Epidemic.” American Journal of Epidemiology, vol. 145, no. 11, 1 June 1997, pp. 959–969, 10.1093/oxfordjournals.aje.a009064. Accessed 22 Mar. 2019.

Pickrell, John. “Timeline: BSE and VCJD.” New Scientist, 2019, www.newscientist.com/article/dn9926-timeline-bse-and-vcjd/.

Weiler, Nicholas. “Alzheimer’s Disease Is a ‘Double-Prion Disorder,’ Study Shows.” Alzheimer’s Disease Is a “Double-Prion Disorder,” Study Shows | UC San Francisco, May 2019, www.ucsf.edu/news/2019/05/414326/alzheimers-disease-double-prion-disorder-study-shows.