Prions are proteins thought to come from neurological tissues in
animals. They are not cellular organisms or viruses. In their
normal noninfectious state, these proteins may be involved in
cell-to-cell communication. When these proteins become abnormally
shaped (i.e., prions), they are able to transform molecules of the
normally shaped protein to the abnormal prion configuration. This
process is repeated numerous times until the number of abnormally
shaped molecules causes overt illness. When consumed in the diet,
prions are thought to be absorbed into the body where, again, they
begin the process of changing their normal protein counterparts
into prions. The specific prions of interest in disease and their
normally configured proteins are those found in mammals. However,
similar proteins occur in other organisms, from chickens to
Prions are associated with a group of diseases called
Transmissible Spongiform Encephalopathies (TSEs). In humans, the
illness suspected of being foodborne is variant
Creutzfeldt-Jakob disease (vCJD)
. The human disease vCJD and
the cattle disease, bovine spongiform encephalopathy (BSE), also
"mad cow" disease
, appear to be caused by the same
agent. Other similar but not identical TSE diseases exist in
animals, but there is no known transmission of these to humans.
Included among these is chronic wasting disease (CWD) of deer and
elk, and the oldest known of these diseases-scrapie-which occurs in
sheep and goats . No early acute clinical indications for TSEs have
been described. After an extended incubation period of years, these
diseases result in irreversible neurodegeneration that becomes the
cause of death.
The most reliable means for diagnosing any TSE is the
microscopic examination of brain tissue-a post-mortem procedure.
Preliminary diagnoses of vCJD are based on patient history,
clinical symptoms, electroencephalograms, and magnetic resonance
imaging of the brain.
The major concern for consumers is the potential contamination
of meat products by central nervous system tissue (brain and spinal
cord) during routine slaughter. This indirect intake of high-risk
tissues may have been the source of human illnesses in the United
Kingdom and elsewhere. Bovine meat (if free of central nervous
system tissue) and milk have shown infective potential in test
animals. Gelatin, derived from the hides and bones of cattle,
appears to be very low risk , especially when produced from
materials originating in countries free of BSE. Based upon many
studies, scientists have concluded that forms of CJD other than
vCJD are not associated with food consumption.
There are no reported human cases of vCJD or bovine cases of BSE
in the United States.. In the United Kingdom, there have been 94
human cases of suspected or confirmed vCJD from 1993, when the
illness was first recognized, through February 2001. Since 1986,
more than 180,000 cases of BSE have occurred there in cattle,
particularly dairy herds. The feeding of rendered TSE-infected
animal by-products to cattle is believed to have caused the
epidemic of BSE. Practices such as this have now been prohibited,
resulting in a dramatic decline in the number of cases.
Cases of vCJD usually present with psychiatric problems, such as
depression. As the disease progresses, neurologic signs
appear-unpleasant sensations in the limbs and/or face. There are
problems with walking and muscle coordination. Sometimes, late in
the course of the disease, victims become forgetful and then
experience severe problems with processing information and
speaking. Uncontrolled muscle twitching and death follow.
All cases of vCJD to date have occurred in individuals of a
single human genotype that is methionine homozygous at codon 139.
About 40% of the total human population belongs to this
methionine-methionine homozygous state. The susceptibility of other
genotypes is not yet known.
No practical detection or inactivation methods exist, at
present. The abnormally shaped prions are resistant to most heat
and chemical treatments. Decontamination methods are so drastic
that food subjected to these processes generally becomes inedible.
Consequently, the key to food protection is obtaining meat from
animals not infected with BSE and protecting against contamination
of food with brain and spinal cord tissue.
Food and Drug
Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a
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