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Mad Cow Disease

What You Need to Know About Bovine Spongiform Encephalopathy

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Eating infected beef can pass prions onto people and pets.

Eating infected beef can pass prions onto people and pets.

Brad Wilson, Getty Images

When it comes to Mad Cow Disease, it's difficult to separate fact from fiction and hard data from supposition. Part of the problem is political and economical, but a lot of it is based in biochemistry. The infectious agent that causes Mad Cow Disease isn't easy to characterize or destroy. Plus, is can be hard to sort through all of the different acronyms used for the scientific and medical terms. Here's a summary of what you need to know:

What is Mad Cow Disease

 

  • Mad Cow Disease (MCD) is Bovine Spongiform Encephalopathy (BSE), except that Mad Cow Disease is much easier to pronounce!
  • The disease is caused by prions.
  • Prions can cross between species (although not all species get diseases from them). Cattle get the disease from eating infected food, such as feed that contains rendered parts of infected sheep. Yes, cattle are grazing creatures, but their diets may be supplemented with protein from another animal source.
  • Cattle don't immediately get sick from eating the prions. It can take months or years for Mad Cow Disease to develop.

Tell Me About Prions

 

  • Simply put, prions are proteins that can cause disease.
  • Prions aren't alive, so you can't kill them. Proteins can be inactivated by denaturing them (e.g., extreme heat, certain chemical agents), but these same processes usually destroy food, so there isn't an effective method to decontaminate beef.
  • Prions naturally occur in your body, so they are not recognized as foreign and don't stimulate the immune system. They have the potential to cause disease, but won't automatically harm you.
  • Disease-causing prions may physically contact normal prions, altering them so that they too can cause disease. The mechanism of prion action is not well understood.

How Can I Get Mad Cow Disease?

Technically, you can't get Mad Cow Disease or Bovine Spongiform Encephalopathy, because you aren't a cow. People who get a disease from exposure to the prion develop a variant of Creutzfeldt-Jakob disease (CJD) known as vCJD. You can develop CJD randomly or from a genetic mutation, completely unrelated to Mad Cow Disease.

 

  • MCD, BSE, CJD, and vCJD are all members of a class of diseases called transmissible spongiform encephalopathies (TSE).
  • It appears that some people are genetically pre-disposed toward developing TSEs. This means that the risk of contracting the disease is not equal for all people. Some people may be more at risk; others may have a natural protection.
  • CJD occurs randomly in about one out of a million people.
  • The inherited version of CJD accounts for about 5-10% of all cases.
  • vCJD may be passed on by tissue implants and theoretically by blood transfusion or blood products.

Tell Me About Beef Safety

 

  • It is not known how much beef has to be eaten to cause infection.
  • Nerve tissue (e.g., brain) and various ground meat products and by-products carry the infectious agents.
  • Muscle tissue (meat) may carry the infectious agent.
  • Rendering or processing foods can (with difficulty) destroy prions.
  • Normal cooking will not destroy prions.

What Does the Disease Do in People?

 

  • TSEs, including vCJD, kill neurons in the brain.
  • The diseases have a long incubation period (months to years), so there is a long time between point of infection and contracting the actual disease.
  • Death of neurons causes the brain to appear like a sponge (areas of open space between groups of cells).
  • All TSEs are presently incurable and fatal.
  • vCJD affects younger patients than CJD (average age 29 years for vCJD, as opposed to 65 years for CJD) and has a longer duration of illness (14 months as opposed to 4.5 months).

How Do I Protect Myself?

 

  • Avoid eating parts of the cow that are likely to carry the infection (brain, ground products, which could include hot dogs, bologna, or certain luncheon meats).
  • Remember that it is possible that muscle may carry the disease, although it would carry the prion in much lower quantities. It's your choice whether to eat beef or not.
  • Milk and milk products are believed to be safe.

The bottom line: Don't eat processed meat from an unknown source. The manufacturer listed on the label is not necessarily the source of the meat.

Mad Cow Disease affects nervous tissue. Until it is known whether only the central nervous system (brain and spinal cord) or whether the peripheral nervous system (e.g., nerves that are in muscles) are affected, there may be risk involved in eating any parts of infected beef. That is not to say that eating beef is unsafe! Eating steaks, roasts, or burgers known to have been made from uninfected herds is perfectly safe. However, it may be harder to know the origins of the meat in processed meat products.

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