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Name: Veronica M.
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: 2001

Is the mad cow disease caused by a virus or a moneran?

Mad Cow is caused by what is known as a prion. These are very unusual infectious agents in that they are not alive. They are actually abnormal versions of proteins that we all have. It was very difficult to discover them because even though the cows were obviously ill, no infectious agent could be isolated. The only agent that could be associated were these abnormal proteins. Not all scientists agree, but the man who discovered them, Stanley Pruisner, received a Nobel Prize.


Neither. Monerans (note that this is not a generally used term, the specialists would call them bacteria or eubacteria) and viruses contain nucleic acid (DNA or, in the case of viruses, sometimes RNA) as the bearers of genetic information. Mad cow disease (BSE) is caused by an infectious protein, and can be infectious without genetic material. The simplest way to think of it is that the BSE causative agent (called a prion) is a protein that is folded in the wrong way. When such a protein sees proteins of its own kind that are correctly folded, it binds to that and forces the other one to fold incorrectly also. In that way the properties are propagated.

This is the way prions (which are incorrectly folded proteins) are thought to cause disease. However there are still some scientists who are not convinced that this is what happens, and who think there must be a virus involved in BSE. This opinion is expressed by a majority of scientists. I mention it to show that scientists do not always agree, even to such fundamental questions as 'what causes BSE'. The only way to find out which view is correct (or both are correct or incorrect) is to conduct experiments to test the hypothesis. In this caes, the ultimate evidence would be if we could synthetically produce the prion protein, and show that this can cause BSE. That proof has not been given yet.

Trudy Wassenaar

The current best guess is neither. BSE (Bovine Spongiform Encephalopathy, mad cow disease) is thought to be caused by a "prion," or proteinaceous infective agent. This protein acts as a template to cause proteins in the brain to mis-fold into shapes in which they do not do their intended jobs, and cannot be cleared by the body's repair machinery.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

Hi Veronica,

Great questions and one that many scientists are working on.

The best understanding at this point is that mad cow disease is caused by something called a prion. Viruses are made of nucleic acid and proteins, but prions are just protein and so not even really complete life forms. This prion is very similar to other proteins that are normally present on cells in the brain and elsewhere. It is believed that when a cow gets this prion protein in its system, the prion causes the normal protein to fold into the wrong shape and then not do its job properly. But there is still a lot of research to be done to understand the process and how it might be prevented.

Laura Hungerford

It is caused by a misfolded protein which can cause other misfolded proteins. This is upsetting to many biologists because it means that an infectious agent does not have to be an can be just a protein...very strange and a REAL problem.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy

Apparently neither, which is what makes it both so fascinating and potentially worrisome. It appears to be caused by something called a prion. As far as scientists can tell, this is a certain kind of misfolded protein. Period. No DNA, no genetic material. Somehow, this misfolded protein causes others to misfold in a similar way, and so on. If a cow eats feed that contains this misfolded protein, it can "catch" the disease. This is a very interesting and mysterious area, where scientists are still largely in the dark. You would be interested to look up Cruetzfeld-Jacob (spelling?) disease. This is the human version of mad cow disease. It turns out that cannibals would pass the disease to one another by eating the infected brains of their dead. Scrapies is the sheep form of mad cow disease, which appears to not be a danger to humans. And now it appears that we have found a form of the disease in some deer and elk populations. Here it goes by the name Chronic Wasting Disease.

Stanley Prussiner (sp?) won the Nobel prize for his work on prions in the 90s; you might want to look up his work on the web.

Paul Mahoney, Ph.D.

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