The Rural Voice, 1991-05, Page 26MAD COW DISEASE: WHAT IS IT?
Is it living or not? Or is bovine spongiform encephalopathy
a new life form in the "twilight zone" of organisms?
by Ian Wylie-Toal
Most of us are aware, in one way
or another, of the infamous disease
bovine spongiform encephalopathy -
BSE for short, or, as it is more fre-
quently called, "mad cow disease." It
first appeared in Britain in 1985, and
is believed to be a form of scrapie, a
sheep disease that has crossed species.
Some details of the disease were
presented by Dr. A. J. Rehmtulla in
the July/90 issue of The Rural Voice.
What is less commonly known,
however, are details about the organ-
ism itself, and how its existence is
challenging the most powerful law of
biology — that all life is based on the
self -replicating molecules of DNA or
RNA, without exception.
The BSE (or scrapie) agent might
just be that exception. It might be an
infectious, self replicating organism
that is simply a protein, containing no
DNA or RNA, a notion that even
its chief proponent, Stanley
Prusiner of the School of Med-
icine at the University of Cali-
fornia, San Francisco, calls
"clearly heretical".
The BSE organism is one of a
group of"unconventional
agents" that cause diseases such
as scrapie in sheep, chronic wast-
ing disease in deer, transmissible mink
encephalopathy, and two human dis-
eases, kuru, and Creutzfeldt -Jacob
disease (CJD). These diseases all
proceed the same way — after infec-
tion, the brain and nerves of the
animal quietly degenerate for several
years until suddenly it starts to lose
co-ordination and mental capacity.
Eventually the animal dies, and, if the
brain is examined, it is found to be full
of holes and mysterious protein fila-
ments. However, in spite of 30 years'
work on the symptoms and mode of
infection of these diseases, very little
is known about the identity of these
unconventional agents. No one has
ever seen them, no one knows what
size they are, and, most importantly,
no one knows how they replicate – no
genetic material has ever been found.
All life must replicate itself. A
rock is clearly not alive, for not only
does it not eat or breathe, it also has no
mechanism by which it can create
copies of itself, — baby rocks that will
carry on its lineage. The importance
of this point becomes apparent when
we start looking at organisms close to
the boundary of life. Like rocks,
viruses neither eat nor breathe.
Neither do they walk, swim, or move
in any way. In reality, viruses possess
none of the attributes that we normally
associate with living beings. Tech-
nically, the only reason viruses are
"alive" is that they are able to re-
produce copies of themselves.
They do this with the self -
replicating molecules deoxyribo-
nucleic and ribonucleic acids (DNA
has caused a lot of excitement (the
only other rule might be that for every
rule there is an exception). However,
as evidence for this notion is based on
the fact that nothing has been found,
interpretation becomes everything.
The current dearth of nucleic acids
from these agents can be taken at face
value, or for those who do not want to
violate the DNA law, it might be that
we haven't looked hard enough for it.
In order to sort out which side, if any,
had the advantage, it's worth taking a
more detailed look at these odd beasts.
Even without DNA controversy,
the BSE or scrapie agents are strange.
First off, they have a long long incu-
bation time, a fact which hampered
research on them for many years.
Kuru, a degenerative disease of the
human central nervous system, is
believed to have an incubation time of
20 to 30 years. Scrapie, which causes
similar symptoms in sheep and goats,
has an incubation time of over
two years. For many years,
research on scrapie was carried
out on sheep, and the long
incubation time created enormous
research problems — experimen-
tal results were not available for
more than two years, and during
that time the flock had to be kept
alive and well. However, in 1961,
it was found that mice will develop
scrapie, reducing the incubation time
to a year or less. More recently,
hamsters have been found to develop
the disease in as little as 60 to 70 days,
increasing the overall speed of the re-
search. These results also indicated
that scrapie was not absolutely species
specific.
The agents are also notoriously
hard to purify. Purification of such
small biological entities is extremely
abstract, being done through a series
of centrifugations. Infected cells are
dissolved, and as much of the cell
material removed as possible. Then
the sub -cellular liquid is spun around
The idea that BSE has no way
of duplicating itself without
any DNA or RNA, is "clearly
heretical" to most scientists.
and RNA), the molecules we call gen-
etic material. The sequence of sub-
units in these large molecules is a code
which, through a series of complex
steps, directs the formation of amino
acids, and the subsequent assembly of
proteins. These proteins then form the
basis of the organism's physical struc-
ture, or, through enzymatic activity (all
enzymes are proteins), direct the for-
mation of the structure and maintain its
life processes.
The presence of nucleic acids as the
foundation of all life is probably the
only absolute rule in biology, so the
existence of unconventional agents and
their possible lack of genetic material
22 THE RURAL VOICE