What Is Mad Cow Disease, and How Does It Cause vCJD?

Medically Reviewed By Kevin Martinez, M.D.
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Mad cow disease, or bovine spongiform encephalopathy (BSE), is a progressive neurological condition that affects cows. Humans can get a version of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD). BSE causes cows to lose coordination, and, in some cases, they may appear to be nervous or violent. These behaviors result in some people referring to BSE as “mad cow disease.”

Humans can get vCJD, which is a variant of BSE, typically from eating parts of a cow with BSE.

This article explains how to recognize the symptoms of mad cow disease, what steps are in place to control BSE, and how it can affect humans.

Variant Creutzfeldt-Jakob disease

Mad cow disease is a condition that affects cows.

Humans can get a version of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD).

Learn more about types of CJD in our article on the condition.

What is BSE?

A person is feeding cows.
Rowena Naylor/Stocksy United

BSE is a condition that affects a cow’s central nervous system, which includes the brain and spinal cord. As highlighted by the Food and Drug Administration (FDA), it is possible to break down the full name as follows:

  • Bovine: This means that the condition affects cows.
  • Spongiform: The brain of a cow with BSE appears to look spongy under a microscope.
  • Encephalopathy: This means that the condition affects the brain.

Due to the way cows with BSE can behave, the condition is commonly known as “mad cow disease.”

What causes mad cow disease?

Scientists believe that a protein called prion causes mad cow disease. There are changes in the prion protein that are harmful to cattle, though scientists do not completely understand why these changes occur.

A cow’s body is unable to detect that the atypical prion protein is present. This means that they are unable to fight off the disease.

How does a cow get mad cow disease?

A cow gets mad cow disease by eating animal feed that contains contaminated parts.

Animal feed can contain parts of cows that are cooked, dried, and ground into a powder. If these cow parts come from a cow with BSE and another cow ingests the atypical prion protein in the animal feed, they can get BSE.

In the United States, there is a ruminant feed ban that prevents the inclusion of contaminated animal parts in animal feed.

Can humans get mad cow disease?

Humans can get a version of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD). Experts believe that people get vCJD by eating food made from cows with BSE.

As of 2019, there were only 232 known cases of vCJD worldwide. The majority of these cases occurred in the United Kingdom, though 4 people with vCJD lived in the United States.

The incubation period for symptoms of vCJD is around 10 years, which means that symptoms may not appear until a decade after you consume the contaminated meat. When they do occur, symptoms of vCJD can be psychiatric and sensory.

Possible symptoms of vCJD include:

vCJD is a fatal condition. Contact your doctor if you have concerns about mad cow disease or vCJD.

Learn more about the different types of CJD.

Can humans get vCJD by eating beef?

Experts believe that it is possible to get vCJD by eating food that comes from a cow with BSE. The Center for Food Safety notes that no CJD cases in the U.S. have occurred as a result of eating beef produced in the U.S.

However, if you are traveling outside of the U.S., avoiding eating beef can reduce your risk of vCJD.

Can humans get vCJD from drinking cow milk?

Researchers have found that it is not possible to get BSE or vCJD by drinking milk or eating dairy products from a sick cow.

How common is mad cow disease?

As the government does not test every cow for BSE, it is not possible to know exactly how common the condition is.

However, the U.S. Department of Agriculture (USDA) carries out surveillance on cows that BSE is most likely to affect. They first carried out major surveillance following the first confirmed case of BSE in an animal in Washington State in 2003.

Out of the 787,711 samples gathered between June 2004 and August 2006, the USDA estimated that there were around four to seven affected animals across an adult cattle population of 42 million.

As of 2016, the USDA gathers 25,000 samples per year. There is currently a very low level of BSE among cattle in the U.S., affecting fewer than 1 per million adult cattle.

Where is mad cow disease found?

Mad cow disease is most prevalent in the U.K., where more than 97% of all BSE cases occurred between 1986 and 2006.

BSE affects fewer than 1 in every 1 million adult cows in the U.S.

Other countries with reports of BSE include:

  • Canada
  • Ireland
  • France
  • Spain
  • Portugal
  • The Netherlands
  • Japan
  • Saudi Arabia
  • Italy
  • Taiwan

If you travel to a country outside of the U.S., avoiding eating beef can help reduce the risk of vCJD.

What are the signs of mad cow disease?

Incoordination is a common sign of mad cow disease. This means that a cow with BSE will find it difficult to get up and walk.

A cow with BSE may also appear to be nervous or act violently.

The incubation period for BSE is around 4–6 years. This means that an atypical prion protein can affect a cow for this length of time before they begin to show signs of the condition.

Once signs of BSE appear, the condition will progressively worsen.

Is mad cow disease fatal for cows?

Mad cow disease is a fatal condition for cows. There are no treatments or vaccines for BSE.

There is also currently no reliable way to test a live cow for BSE. However, scientists can carry out tests after the cow dies to check for an atypical prion protein in the brain.

How is mad cow disease controlled?

In the U.S., the FDA issued a ruminant feed ban in 1997. This placed restrictions on certain materials in animal feed for cattle and other ruminant animals.

An update to the ruminant feed ban came into effect in 2009. This update banned the use of high risk cattle materials in all animal feed.

Examples of cattle materials prohibited in animal feed (CMPAF) according to the 2009 update include:

  • entire carcasses of cattle with BSE
  • brains and spinal cords of cattle ages 30 months and older
  • entire carcasses of cattle that have not been inspected and passed for human consumption
    • This does not apply if the cattle are younger than 30 months old or if the brains and spinal cords are effectively removed.
  • tallow from cattle with BSE
  • tallow from CMPAF that contains over 0.15% insoluble impurities
  • beef from CMPAF that is mechanically separated

In order to help control mad cow disease with the implementation of the ruminant feed ban, an individual can face consequences if they do not comply. If they do not make immediate corrections, consequences can include:

  • a warning letter
  • seizure
  • injunction
  • criminal penalties

Is mad cow disease contagious?

Mad cow disease is not contagious. This means that a cow cannot pass it on to another cow by being near them.

Similarly, vCJD — which is the variant of BSE that humans can get — is not contagious.

Can BSE affect other animals?

While BSE refers to a condition that affects bovines, or cows, other animals can get spongiform encephalopathy. These animals include:

  • sheep
  • goats
  • deer
  • elk
  • mink
  • cats

Cats are currently the only common household pet with a known spongiform encephalopathy, which is called feline spongiform encephalopathy (FSE). There are no known cases of FSE in the U.S.

Other animals can carry viruses that may infect or cause illness among humans. This includes bird flu, or avian flu, which is an influenza virus that spreads among birds and, in some cases, humans. Learn more about bird flu.


Mad cow disease, or BSE, is a progressive neurological condition that affects cows. Specifically, it affects their coordination and can cause them to be nervous or aggressive.

They get the condition by eating animal feed containing contaminated cow parts. Humans can get a version of BSE called vCJD by eating meat from affected cows. Neither vCJD nor BSE is contagious.

BSE affects fewer than 1 in every 1 million adult cattle in the U.S. If you travel to a different country, avoiding eating beef can help reduce the risk of vCJD.

Contact your doctor if you have visited a country with known cases of BSE and you have concerns about vCJD.

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Medical Reviewer: Kevin Martinez, M.D.
Last Review Date: 2022 Jun 27
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