What is mad cow disease, and does it infect people?
People cannot get mad cow disease. But in rare cases they may get a human form of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD), which is fatal.
This can happen if you eat nerve tissue (the brain and spinal cord) of cattle that were infected with mad cow disease. Over time, vCJD destroys the brain and spinal cord.
There is no evidence that people can get mad cow disease or vCJD from eating muscle meat—which is used for ground beef, roasts, and steaks—or from consuming milk or milk products.
People with vCJD cannot spread it to others through casual contact.
People who have spent a lot of time (at least 3 months) in places where mad cow disease has been found are not allowed to give blood in Canada or the United States.footnote 1, footnote 2 This is to help prevent vCJD from spreading.
What causes mad cow disease and variant Creutzfeldt-Jakob disease (vCJD)?
Experts are not sure what causes mad cow disease or vCJD.
The leading theory is that the disease is caused by infectious proteins called prions (say "PREE-ons"). In affected cows, these proteins are found in the brain, spinal cord, and small intestine. There is no proof that prions are found in muscle meat (such as steak) or in milk.
When a cow is slaughtered, parts of it are used for human food and other parts are used in animal feed. If an infected cow is slaughtered and its nerve tissue is used in cattle feed, other cows can become infected.
People can get vCJD if they eat the brain or spinal cord tissue of infected cattle.
How common are mad cow disease and vCJD?
The first case of vCJD was reported in 1996. Since then, there have been a few cases of vCJD reported in the world. Most of the cases have been in countries that are part of the United Kingdom (England, Scotland, Wales, and Northern Ireland).
Since May 2003, 19 cows suspected of having mad cow disease have tested positive for BSE in Canada. No meat from these cows entered the human food supply. For more information on BSE in Canada, contact the Canadian Food Inspection Agency or see the agency's website: www.inspection.gc.ca.
What are the symptoms of vCJD?
Variant Creutzfeldt-Jakob disease (vCJD) causes the brain to become damaged over time. It is fatal. Symptoms include:
- Tingling, burning, or prickling in the face, hands, feet, and legs. But there are much more common illnesses that cause these same symptoms. Having tingling in parts of your body does not mean you have vCJD.
- Psychotic behaviour.
- Problems moving parts of the body. As the disease gets worse, a person is no longer able to walk.
If a person does eat nerve tissue from an infected cow, he or she may not feel sick right away. The time it takes for symptoms to occur after you're exposed to the disease is not known for sure, but experts think it is years.
How is vCJD diagnosed?
There is no single test to diagnose vCJD. Doctors may think that a person has vCJD based on where the person has lived and the person's symptoms and past health. Imaging tests, such as an MRI, may be done to check for brain changes caused by vCJD.
Researchers are now trying to develop a blood test that looks for vCJD. But no blood test is available at this time.
A brain biopsy is the only way to confirm a diagnosis of vCJD.
How is vCJD treated?
There is no cure for vCJD. Treatment includes managing the symptoms that occur as the disease gets worse.
The following health organizations are tracking and studying mad cow disease and variant Creutzfeldt-Jakob disease (vCJD). Their websites contain the most up-to-date information about these diseases.
- Health Canada answers frequently asked questions about mad cow disease and vCJD and provides information about infection control and food inspection. Visit www.canada.ca/en/health-canada/services/food-nutrition/food-safety/mad-cow-disease.html for more information.
- Canadian Food Inspection Agency (CFIA) answers questions and provides updates on BSE in North America. It also offers information about infection control and food inspection. Visit www.inspection.gc.ca/animals/terrestrial-animals/diseases/reportable/bse/eng/1323991831668/1323991912972 for more information.
- U.S. Centers for Disease Control and Prevention (CDC) provides up-to-date information about mad cow disease and variant Creutzfeldt-Jakob disease (vCJD), including tracking, prevention, travel precautions, and food inspection. Visit www.cdc.gov/prions/bse/index.html for more information.
- The World Health Organization (WHO) website offers information about mad cow disease and vCJD cases around the world and provides infection control guidelines. Visit www.who.int/csr/disease/bse/en for more information.
- American Red Cross (2009). Eligibility requirements: Donating blood. Available online: http://www.redcrossblood.org/donating-blood/eligibility-requirements.
- Canadian Blood Services (2016). The ABCs of eligibility. Available online: https://www.blood.ca/en/blood/abcs-eligibility. Accessed June 3, 2016.
Current as of: January 26, 2020
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Anne C. Poinier MD - Internal Medicine
Adam Husney MD - Family Medicine
W. David Colby IV MSc, MD, FRCPC - Infectious Disease
Leslie Tengelsen PhD, DVM - Zoonotic Disease
Current as of: January 26, 2020