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Mad Cow
Disease
Mad Cow Disease is the common
name for a degenerative neurological disease of
cattle called Bovine Spongiform Encephalopathy (BSE).
BSE is one example of a class of neurological
diseases called Transmissible Spongiform
Encephalopathies (TSE). The disease has become a
household word around the world largely due to
an outbreak of the disease in the United Kingdom
involving over 183,000 confirmed cases [1].
While the transmission means for the disease is
still not well understood, it is proposed that
the outbreak may have originated from feeding
the cattle meat and bone meal that was derived
from sheep that were infected with scrapie, a
TSE commonly found in sheep and goats. The
spread of the disease was probably accelerated
by feeding meat and bone meal from infected
cattle back to young calves.
While BSE is exclusively a disease of cattle,
the outbreak in the United Kingdom coincided
with over 150 human cases of a rare brain
disorder called Variant Creutzfeld-Jakob Disease
(VCJD). While the transmission mechanism is
still being debated, the U.S. Center for Disease
Control has indicated that the persons who
contracted VCJD in the United Kingdom were
infected through consumption of cattle products
from cattle infected with BSE [2].
Variant Creutzfeld-Jakob Disease is a separate
disease from classic Creutzfeld-Jakob Disease.
The classic disease apparently develops
spontaneously and primarily affects older
patients with a median age at death of 68 years.
The median age at death for the patients with
VCJD in the United Kingdom is 28 years [2].
TSE diseases are found in many species including
BSE in cattle, scrapie in sheep and goats,
transmissible mink encephalopathy in mink,
feline spongiform encephalopathy in cats,
chronic wasting disease (CWD) in deer and elk
and kuru, classic CJD,
Gerstmann-Straussler-Scheinker syndrome, fatal
familial insomnia, and VCJD in humans.
The agent that causes BSE is thought to be a
prion, which is an abnormal form of a common
protein that has the ability to reproduce
itself. The agent is only found in brain tissue,
the spinal cord, and in the retina of the eye,
and it is only found in these locations in
cattle over 24 months of age (with rare
exceptions).
Since 1989, the Animal and Plant Health
Inspection Service (APHIS) has prohibited the
importation of live cattle and cattle products,
including rendered protein products, from
countries where BSE is known to exist. In 1997,
these restrictions were extended to include all
of the countries in Europe. On December 7, 2000,
APHIS extended the ban to include all imports of
rendered animal protein products,
regardles of species. This was due to concern
about potential cross-contamination of feed.
In 1997, the FDA prohibited the use of
mammalian protein in animal feeds given to
cattle and other ruminants.
The discovery of BSE infected cows in Canada in
2002 and in the U.S. in 2003 may cause
additional restrictions to be placed on the use
of animal byproducts in animal feed. If grease
from rendered animal carcasses is banned from
feed, biodiesel production might become the best
opportunity for disposing of this important
product of the animal rendering
industry.
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References:
1.
http://www.cdc.gov/ncidod/diseases/cjd/bse_cjd_qa.htm
2.
http://www.cdc.gov/ncidod/diseases/cjd/cjd_fact_sheet.htm
Websites for additional information:
www.aphis.usda.gov/oa/bse
www.fas.usda.gov/dlp/BSE/bse.html
www.BSEinfo.org
www.afia.org
www.fda.gov/cvm/index/bse/bsetoc.html
www.cdc.gov/ncidod/diseases/cjd/cjd.htm
www.animalprotein.org
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