You may be wondering what a prion is and why you
should care. Well, your ears might perk up a lot if you hear the words
- 'Mad Cow Disease'. That disease is caused by a transmissible prion.
Prion related diseases have been recognized for years. However, until recently we did not realize what caused them.
What
we did know about them is that they caused dementia. People gradually
lost their ability to reason and remember things. We also noticed that
there were typical changes in the brain when looked at during autopsy.
Prions
became famous when Kuru was found among the Fore people of New Guinea.
In this disease, people would get unsteady gait, tremors, and slurred
speech. The interesting thing was that only women and children seemed
to get the disease.
It was finally noticed that when a person
died, his family would eat him as a way to honor the dead. But only the
women and children participated in this practice. Scientists found that
by stopping this practice, the incidence of the disease suddenly
plummeted.
Further research in Kuru found that the cause was a
protein - not a bacteria or virus. Furthermore, there was no way to
destroy this protein by filtering or cooking. Proteins are formed as a
long molecule that then folds over and over. The shape of the folded
molecule determines how it functions.
It also determines what
enzymes in the body are needed to break it down when it is no longer
needed. The prion works by causing a protein in the brain into the
wrong shape. Therefore it does not work and the brain makes more and
more of the chemical - trying to make enough of the protein to fill the
need of the body.
The real devastation of the disease though is
that the resulting misshapen chemical does not have enzymes in the body
that can break it down! So the protein builds up in large amounts that
become toxic to brain cells and finally cause them to die.
Once
scientists realized the cause and effect of this prion, several other
known diseases were found that fit this pattern. These included scrapie
(found in sheep), chronic wasting disease (found in deer and elk),
Creutzfeldt-Jakob disease and fatal familial insomnia in humans, and
bovine spongiform encephalopathy in cattle (also known as mad cow
disease).
What is not known is if there is a connection to prion
disease and Alzheimer's disease. We have recognized several genetic
mutations that can cause Alzheimer's disease and form prions in the
body of the person with the mutation. However, this does not account
for the total number of those with Alzheimer's disease.
One piece
of evidence that is suspicious. It is known that people who habitually
eat meat more than four times a week have three times as much chance of
getting Alzheimer's disease than vegetarians. However, at least some of
this statistic could be related to increasing arteriosclerosis
(hardening of the arteries) in those that eat meat.
If there is a
prion that causes Alzheimer's disease that you can get from eating
meat, why can't you easily prove or disprove it? Well, here is the
problem. The currently know prions cause disease fast enough that you
can put the prions into lab animals like white mice and they get the
disease. However, have you ever seen a mouse live as long as someone
who has Alzheimer's disease? Of course not.
We do know that
prions come in strains that vary widely in the amount of time that it
takes to cause the disease. So, here is the big question. What if there
were a prion that caused disease in humans, but it took longer to cause
problems than the lifespan of the animal that it came from? For
instance, if cows live 10 years but it takes 50 years for the disease
to show up, you would never - ever see the disease in cows even if they
carried the disease. The same goes for chickens, sheep and pigs. You
see the problem?
At this point, we do know that one fact - that
you get only 1/3 as much dementia if you are a vegetarian. Until more
is known about what is really in fact safe to eat, vegetarians have a
leg up on carnivores on this issue.
