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Mad Cow Disease for Humans: Variant Creutzfeldt-Jakob Disease

Written by Risa Nguyen, Edited by Olivia McCollum

What are prions?

Prions are infectious agents that degrade the nervous system. They differ from many other pathogens in that they are not living organisms, as prions lack genetic material.  Prions are misfolded proteins that bind to normal proteins in a host’s cells and force them to misfold. Sometimes, prions can be transmitted by consuming meat from an infected animal.1 The most common example of prion transmission is caused by eating cattle meat infected with prions that cause bovine spongiform encephalopathy (BSE).


Characteristics of bovine spongiform encephalopathy

Bovine spongiform encephalopathy is a prion disease that affects cattle. Despite the exact origins of BSE being unknown, researchers suggest that the disease is spread through cattle feed contaminated with tissue from a sick cow.2 The disease is named after the distinct microscopic appearance of an infected cow’s brain tissue. In BSE cases, the cow's infected brain develops masses of misfolded proteins, leading to hole-like formations on the brain's surface, resembling a sponge under microscopy. The symptoms of BSE are incoordination and the sudden onset of violent behavior, giving rise to the colloquial term “Mad Cow Disease.”3 Unfortunately, there are no preventive measures for BSE. Once a cow has been infected with BSE, the disease cannot be cured, and it is always fatal.


Short history about a BSE outbreak

In the 1980s, the United Kingdom experienced an outbreak of BSE, which caused a severe economic crash in the meat production industry. Over 10 years later, people reported cases of a similar infection in humans, which was then identified as variant Creutzfeldt-Jakob disease (vCJD).2 Fortunately, with dedicated research and agricultural policy implementation, both BSE and vCJD cases are extremely rare around the world.


Characteristics of variant Creutzfeldt-Jakob disease

Humans can get infected with the human equivalent of BSE, variant Creutzfeldt-Jakob disease. vCJD is spread to humans through consuming prion-contaminated cow meat. The time between exposure to the prions and symptom onset, the incubation period, for vCJD is about ten years.4 The symptoms of vCJD are depression, reduced coordination skills, dementia, and the sensation of pins and needles.4 A person with vCJD can survive up to a year once symptoms appear; however, like BSE, it is never reversible and always fatal. The disease is especially hard to detect because of its long incubation period, and it cannot be definitively diagnosed until a brain tissue sample is taken after death.4


Research on potential transmission routes of vCJD

The possible routes of transmission of vCJD have been a topic of interest amongst the scientific community for decades. A scientific review by Alexis Pozzo di Borgo studied the possible transmission of vCJD through blood transfusions. In the late 1990s, an isolated incident occurred, in which five patients developed what was likely to be vCJD after receiving nonleukodepleted blood from a donor who later developed vCJD.5 It was possible, however, statistically unlikely, that these patients got vCJD from eating infected meat. After performing a cohort study of 787 patients who received blood from donors with vCJD over 21 years, researchers concluded that risk of transmission was significantly reduced due to strict preventative interventions to protect the blood supply, including the adoption of universal leukoreduction in 1999 and deferring blood donors who lived in the UK during the peak of the BSE epidemic, and vCJD deferral criteria are being lifted.5 Continuing to understand how vCJD spreads is important because of its 100% fatality rate, which raises major concerns about which populations are most vulnerable to being infected.


Where are we now?

Researchers rushed to find the cause of the BSE outbreak happening in various farms around the UK. In this search, they learned that prions were concentrated in brain matter, which was present in many animal feeds.2 Prions are highly resistant to high temperatures, making it important for farmers to prevent prions from making contact with food. This discovery led farmers to stop using cattle brains in animal feed. Cattle farmers culled infected cows to prevent further transmission.2 Now, there are very few cases of either BSE and vCJD, with almost no cases being reported in the last decade.2 Although both diseases are rare now, prions’ resistance to many disinfection methods and their ability to stay dormant in the host create concern for underreported cases. More research is needed to understand how and why prions are misfolded and how they spread misfolds to nearby proteins, despite not being living organisms.

References

  1. John Hopkins Medicine. Prion Diseases. Johns Hopkins Medicine. Published 2025. https://www.hopkinsmedicine.org/health/conditions-and-diseases/prion-diseases

  2. CDC. Bovine Spongiform Encephalopathy (BSE). Bovine Spongiform Encephalopathy (BSE). Published May 10, 2024. https://www.cdc.gov/mad-cow/php/animal-health/index.html

  3. U.S. Food and Drug Administration. All About BSE (Mad Cow Disease). U.S. Food and Drug Administration. Published July 23, 2020. https://www.fda.gov/animal-veterinary/animal-health-literacy/all-about-bse-mad-cow-disease

  4. CDC. About Variant Creutzfeldt-Jakob Disease (vCJD). Variant Creutzfeldt-Jakob Disease (vCJD). Published May 13, 2024. https://www.cdc.gov/variant-creutzfeldt-jakob/about/index.html

  5. Pozzo A, Rochette S, Amaury Gaussen, et al. Transmission of Variant Creutzfeldt-Jakob Disease Through Blood Transfusion and Plasma-Derived Products: A Narrative Review of Observed and Modeled Risks. Transfusion medicine reviews. 2023;37(3):150747-150747. doi:https://doi.org/10.1016/j.tmrv.2023.150747

This post is not a substitute for professional advice. If you believe that you may be experiencing a medical emergency, please contact your primary care physician, or go to the nearest Emergency Room. Results from ongoing research are constantly evolving. This post contains information that was last updated in May 2026.


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