The Rural Voice, 1991-05, Page 28FARMERS!
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Hubert Schilbe
236-4792
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Larry Campbell
928-2855
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786-4423
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1990 Ltd.
Ron McCann, Manager
224 Suncoast Dr., Goderich (next door to Fisher Glass)
24 THE RURAL VOICE
Edinburgh, calls the agent a "virino"
and describes it as a small piece of
nucleic acid that uses the host's own
proteins to create a protective coating
(Pain, 1990.)
Moira Bruce and Dickinson have
worked with scrapie for many years
and have isolated over 15 different
strains of the organism. They feel the
existence of these strains, which are
distinguished largely on the basis of
their incubation time in mice, offers
indirect evidence for the presence of
genetic material. In a paper published
in 1987, Bruce and Dickinson offer
further evidence, claiming to have
found spontaneous mutation within
one strain of scrapie, 87A. When
mice are infected at high dosages with
this strain, a different strain, 7D will
often appear. 7D only occurs in con-
junction with 87A, and occurs even
after 87A has theoretically been pur-
ified of any other scrapie strains.
They say "it is highly likely that the
7D in tissues of mice infected with
87A is generated de novo (afresh) at
each passage by mutational change
from 87A during the incubation
period. The established fact that many
different strains exist and the consider-
able evidence that mutation can occur
lead to the conclusion (the) scrapie
agent has its own independently repli-
cating genome."
So, what to make of this all? Here
we have ari organism that no one has
ever seen, which offers compelling
evidence that it may or may not have
genetic material. Great. Isn't that
how so much science ends up? On the
one hand this, on the other hand that.
But it's understandable when you look
at what scientists are dealing with.
We are so used to large, tangible
objects, that when molecular
biologists tell us they have "found"
the organism that causes some disease,
we have this mental image of them
holding one, able to turn it over and
examine it. Often, as in this case,
everything is indirect and abstract.
An organism is "found" because one
layer of centrifuged cell sludge causes
more infection than the layers above
and below it, so all the infectious
particles are in that layer. It's all
round -about, trying to get something
tangible out of the intangible.