Mad cow disease is caused by misfolded infectious proteins called prions , which spread in cattle mainly through contaminated feed made with infected animal tissues.

Quick Scoop on What Causes Mad Cow Disease

Mad cow disease (technical name: bovine spongiform encephalopathy, or BSE) is not caused by bacteria, viruses, or parasites, but by abnormal versions of a normal brain protein.

These abnormal prion proteins trigger a chain reaction in the brain:

  • They cause normal prion proteins to misfold.
  • Misfolded proteins clump together.
  • Over time, they damage brain tissue, creating a “spongy” appearance under the microscope.

How Cattle Get Mad Cow Disease

The main driver of the original BSE epidemic was what cattle were fed.

Key points:

  • Cows were given meat-and-bone meal made from other animals as a protein supplement.
  • Some of this feed contained tissues (especially brain and spinal cord) from animals already carrying prions (either cattle with BSE or sheep with a related disease called scrapie).
  • Young calves eating this feed became infected, allowing the disease to amplify through herds.

There is also evidence that:

  • A spontaneous or older prion disease (possibly scrapie in sheep) may have mutated and jumped into cattle through this feed route.
  • Once established, recycling infected cattle tissues back into feed greatly magnified the outbreak.

Timeline and Incubation

Mad cow disease develops very slowly:

  • After a cow is infected, it usually takes years before symptoms appear.
  • During this long incubation period, the brain is gradually accumulating abnormal prions and damage.

This slow burn is one reason the problem was hard to spot in the early years of the 1980s–1990s outbreak, especially in the UK.

Can Humans Get It?

Mad cow disease in cattle is linked to a related human condition called variant Creutzfeldt–Jakob disease (vCJD).

What we know:

  • The same strain of prion that causes BSE in cattle can cause vCJD in humans.
  • People who developed vCJD had typically eaten beef products contaminated with BSE prions, especially tissues like brain or spinal cord that carry high levels of prion.
  • Only a small number of people worldwide have developed vCJD, but the disease is uniformly fatal.

Most expert sources emphasize:

  • There is no evidence that ordinary muscle meat (steak) or milk is a major source of prion transmission, because prions concentrate in nervous tissue and certain gut tissues.

Why It’s Still a Trending Topic

Mad cow disease periodically comes back into the news when:

  • A new BSE case is detected in cattle, even if isolated and controlled.
  • There are updates to food safety rules , such as bans on feeding certain animal by-products to ruminants or stricter removal of high‑risk tissues from the food chain.
  • Public health agencies publish new overviews on the very low current risk to consumers due to these controls.

Even in 2025–2026, discussions on forums and news sites often revolve around:

  • “Is beef still safe?”
  • “Can this happen again if rules are relaxed?”
  • “What exactly are prions and why are they so hard to destroy?”

Modern regulations—like prohibiting animal protein in cattle feed and removing specific risk materials (brain, spinal cord, certain intestines) from the food supply—have dramatically reduced the risk compared with the 1990s.

Core Cause in One Line

Mad cow disease is ultimately caused by infectious misfolded prion proteins , and the historic outbreaks happened because cattle were fed feed containing tissues from prion‑infected animals, allowing those prions to spread and amplify in herds.

Information gathered from public forums or data available on the internet and portrayed here.