Mad Cow Disease
Name: Veronica M.
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.
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.
PG Research Foundation, Darien, Illinois
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.
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 organism...it can be just a
protein...very strange and a REAL problem.
Peter Faletra Ph.D.
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.
Click here to return to the Molecular Biology Archives
Update: June 2012