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Most recent posting below. See other blog postings in the column to the right.

There are Cows and There are Mad Cows, or What are the Stakes in Steak?

September 01, 2004

By Mark B. Levin, M.D. and Louis J. Tesoro, M.D.

We have heard much recently about Mad Cow Disease (Bovine Spongiform Encephalitis or BSE), but not much about what it actually is, what it does to the poor cow, how it can affect us and how we can avoid trouble

To understand the nature of BSE and why it affects cows and humans, a brief lesson in physiology is necessary. All animals and plants are all made up of cells. Among the products manufactured by cells to enable us to grow and function are proteins. Some of these proteins are called enzymes. Enzymes act like a biologic catalyst, making some of our internal biochemical reactions possible and others more efficient. Although it may not be esthetically pleasing to think of ourselves as a collection of cells and chemicals, that is exactly what we are. The way these billions of components are put together and how the finally constructed organism responds to environmental influences determines who we are as individuals. Simple! If a component of the system is aberrant, it can really foul up the works.

BSE is caused by the accumulation of strands of an aberrant form of a normal protein in nerve cells, called a "prion". Because a prion is simply a protein, it can not travel or reproduce on its own. An animal or human with prion disease, therefore, is not contagious by contact (or by close contact). You actually have to consume the particles to become infected (see below). Since a prion differs from the normal proteins produced in the nerve cell, it is not recognized by enzymes that are responsible for cleaning up stray proteins. Prions accumulate within the nerve cell in a tiny bubble called a vacuole. When enough of these prion-filled bubbles accumulate in the nerve cells (brain) of a cow, the brain takes on a sponge-like microscopic appearance and makes the cow act in a bizarre fashion.

As you might suspect, these unpleasant accumulations of vacuoles are not restricted to the brain. They are found in the nerves that emanate from the brain by way of the spinal cord and wind their way into muscle tissue. We eat the muscle tissue (meats). Hence, the secret of the prion’s ability to cause human disease. (Actually, some humans eat animal brain tissue, as well – a far more efficient way to acquire prions!) The exact mechanism that enables the ingested prions to enter brain tissue is not yet clear. When it does gain entry, however, a process similar to that found in the cow takes place in the human. The clinical picture exhibited by people affected by prion disease is markedly similar to the neurologic deterioration seen in a familial disease called Creutzfeldt-Jakob Disease (CJD). Because prion disease is similar to the familial form of CJD, but not actually identical, the condition it causes has been termed "new variant Creutzfeldt-Jakob Disease (nvCJD)." Prion disease can affect other animals, too. A more common one affecting sheep is called "scrapie." The collection of prion diseases is termed TSEs (Transmissible Spongiform Encephalopathies).

Now that you are informed about and frightened by prions, we remind you that, although it is certainly a condition worth avoiding, it is uncommon in humans and easily recognized in cows (they circle continuously and eventually collapse). You might wisely ask why, if we know what prion disease is and how humans acquire it, do we not prevent cow nerve tissue from entering our food supply? Although the answer is simple from a scientific and mechanical viewpoint, it is socially and economically complex.

Cow feed is commonly laced with the pulverized remains of other animals, including slaughtered cows. The feed that contains prions can trigger BSE in the feeding herd. In the slaughterhouse process of preparing cow meat (beef) for the human market, the meat is first manually cut from the bone, These are our steaks. The meat that remains close to the bone (and that contains most of the nerve tissue) is then removed by an air-pressure machine that is far more efficient and economical than manual removal. These residual morsels are our fast food hamburgers, our hot dogs and our pizza meat toppings. To leave these last bits on the bone would cost the meat industry millions of dollars in lost sales. When BSE and nvCJD became an issue in other countries, health and environmental groups attempted to have the air-pressure method prohibited by law. Our government lawyers argued against the prohibition because of the projected negative economic impact on the industry (and hence the national economy). They convinced the judge in the case that the risk to public health was extremely small, since our record keeping system on the origin of the cows was exemplary. Recent events have, of course, called this contention into question. The affected animal found in Washington State was recorded in the U.S. to be a calf, but it actually came from a Canadian herd and has had three calves of her own. Of this herd of eighty-one animals, less than half have been identified and located by our "exemplary" record keeping system.

Since the government and industry are less than perfect in watching over issues that affect our personal well being, how should we conduct ourselves? It is apparent to us that we have two choices. The first is to join the ranks of vegetarians and avoid meat intake altogether. For those in the population who wish to maintain some semblance of their former lifestyle but minimize their risk, it makes sense to avoid the marketed products that contain the air-pressure-removed meat. If hamburgers are your life’s sine qua non, buy sirloin and a grinder and make your own. Eat the eye of the T-bone steak but do not chew on the sweet meat adherent to the bone. Opt for turkey or chicken franks instead of beef franks. Choose broccoli on your pizza rather than a meat topping. There are also some quite tasty vegetable burger-substitutes available in the freezer section of the supermarket.

Being glass-half-full people, we can imagine some good coming of this situation. Perhaps, because of the threat of nvCJD, our population will begin to avoid high fat, high calorie, high salt foods served in fast-food restaurants. In addition to being a wise decision with respect to the acquisition of prions, this would also have a positive impact on the rate of obesity and heart disease in the U.S.

Dr. Mark B. Levin

Dr. Levin was a member of the staff at The Pediatric Group starting in 1977. He was an attending Pediatrician at the Medical Center at Princeton, Chairman, Department of Pediatrics, Medical Center at Princeton, 1984 to 1986, 1989 to 1992, and past President, Medical and Dental Staff, Medical Center at Princeton, 1987 to 1988. Dr. Levin served on numerous Departmental and hospital committees. He published original articles both while at Upstate Medical Center in Syracuse and at The Pediatric Group.Dr. Louis J. Tesoro

Dr. Tesoro has been a member of the staff at The Pediatric Group since 1988. Dr. Tesoro is Chairman, Department of Pediatrics, Medical Center at Princeton, 1996 to present and Attending Pediatrician, Medical Center at Princeton, 1988 to present. He has served on several Departmental and hospital committees, lectured at the Universiy of Pennsylvania and has published original articles both while at The Children's Hospital of Philadelphia and at The Pediatric Group

Moderated by Helen Rose.

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