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Today is :
Archives (2001)
Mad cow disease: know
the risks
by Junelysn S. dela Rosa |
January-March
2001
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Years after it was supposedly vanquished, the
brain-eating disease that kills cows and some people who eat
them is on a comeback. Today, the mad cow disease or the bovine
spongiform encephalopathy (BSE) is again breaking headlines
and is stirring a lot of havoc and public fear all around
the globe. Here are some of the most frequently asked questions
and answers regarding BSE.
Q. What exactly is BSE?
A. BSE or mad cow disease is one of several fatal brain diseases
called transmissible spongiform encephalopathies (TSEs). BSE
is a progressive, lethal central nervous system disease of
cattle. The brain looks like a sponge, hence the term spongiform
because the brain contains vacuoles. In 1982, Stanley Prusiner,
a biochemist at the University of California suggested a radical
idea-that various encephalopathies were caused by a rouge
protein-a "prion".
Q. What are prions?
A. Prions or PrP proteins are abnormal rouge proteins able
to convert normal proteins into more abnormal forms. They
contain no nucleic acids (DNA or RNA). They consist of a single
molecule containing about 250 amino acids, termed the PrP
protein.
Abnormal PrP proteins are folded in a way that
allows them to resist normal protease degradation. Over time,
this results to a build-up of aggregates of PrP, especially
in neurons in the brain.
Q. Is there a risk that BSE will infect people?
A. Yes. The TSEs were once considered unlikely to infect other
species. However, in 1996, the UK government acknowledged
that eating contaminated meat was the "most likely explanation"
why 10 young people had the variant Creutzfeldt-Jakob disease
(vCJD). The awkward name reflects the similarity to Creutzfeldt-Jakob
disease (CJD), a deadly brain illness that strikes about one
person per million per year, due to genetic or unknown causes.
While CJD mainly affects the elderly, vCJD appears
among younger people. The quick and gruesome death starts
with mood swings, numbness, and uncontrolled body movements.
Eventually, the mind is destroyed, somewhat like Alzheimer's,
another brain-wrecking disease. Many vCJD victims die four
months after symptoms appear. There is no treatment.
Q. What about TSEs in other animals?
A. Scrapie is the TSE disease in sheep and goats. Mink and
North American mule deer and elk can contract TSEs. A neurological
disease in household cats and in ruminant and feline species
in zoos has been linked to BSE. Most cases in such animals
appear to have occurred in the UK.
Q. What is the infectivity of BSE-containing
material?
A. Infection is dose-dependent but the required dose for BSE
transmission to cattle is small. If consumed, 500 mg to 1
g infected brain appears sufficient to infect. The BSE agent
has been found only in brain tissue, spinal cord and retina
of cattle naturally affected with BSE. It has not been found
in meat or milk. Similarly, it is not transmissible through
meat or milk. Traces of the BSE agent are detectable in the
small intestines of calves that had been fed large doses of
meal from BSE-infected animals.
Q. What about the safety of human and veterinary
vaccines made from bovine products?
A. The World Health Organization (WHO) reported that human
and veterinary vaccines from bovine materials carry the risk
of transmission of animal TSE agents. It was recommended that
the pharmaceutical industry avoid the use of bovine materials
and materials from other animal species in which TSEs occur.
These include nine vaccines regularly given to millions of
American children, including common vaccines to prevent polio,
diptheria, and tetanus. These precautions apply to the manufacture
of cosmetics as well.
Q. Can vCJD be
transmitted through blood transfusions?
A. In 1997, new animal studies suggested that vCJD could be
transmitted through the blood. White blood cells, which form
part of the immune system and are found in the lymph glands,
were isolated as one of the high-risk tissues for BSE infection.
As a result of this concern, the British government required
the removal of white blood cells from donated blood.
The fact that vCJD could enter the lymph system
raised further possibility that it might infect the tonsils
or appendix, both of which contain large amounts of lymphoid
tissue.
Q. How long is the incubation period of vCJD?
A. The incubation period is yet unknown. Some experts believe
that it could be as long as 30-40 years. In August last year,
a new research indicated the existence of a hidden "subclinical"
form of BSE, which produced no symptoms but could nonetheless
be infectious. This raised the frightening possibility that
not only cattle but sheep, pigs and poultry exposed to BSE
via animal feed may secretly harbor the disease.
Q. When did the BSE outbreak start?
A. The illness was first identified in 1985 by a vet who was
puzzled by the odd symptoms exhibited by sick cows in a dairy
farm in Southern England. Scientists found evidence linking
the new illness to the sheep disease-scrapie. It was technically
named Bovine Spongiform Encephalopathy (BSE) but it became
popularly known as mad cow disease-because of the way infected
cattle behaved.
Scientists believed that BSE was created when cows were fed
scrapie-infected feeds manufactured from abattoir offcuts.
Experts theorized that new manufacturing techniques in feed
production in the 1970s and 1980s allowed a resilient strain
of scrapie to enter the feed and for it to re-emerge in a
new form in cattle disease---BSE.
Q. How widespread is the BSE outbreak?
A. The WHO says that approximately 180,000 cases of BSE have
been reported in Britain and relatively small numbers of BSE
cases (in total approximately 1300) have also been reported
in native cattle in Belgium, Denmark, France, the Republic
of Ireland, Liechtenstein, Luxembourg, the Netherlands, Portugal,
and Switzerland.
Germany and Spain reported their first native
cases in November 2000. A couple of dozen cases have also
been reported in Canada, the Falkland Islands (Islas Malvinas),
Italy and Oman.
Q. What are the
measures that can reduce exposure to the BSE agent?
A. Here are the measures that are recommended by WHO to reduce
exposure to the BSE agent:
- All countries must prohibit the use of ruminant tissues
in ruminant feed and must exclude tissues that are likely
to contain the BSE agent from any animal or human food chain.
- This means that brain tissue, spinal cord, intestines should
not be eaten. That is, they should not be used in preparing
"nilagang baka", "sisig" and "goto".
- All countries are encouraged to conduct risk assessments
to determine if they are at risk for BSE in sheep and goats.
It is advised that any tissue which may come from deer or
elk with chronic wasting disease (CWD, a transmissible spongiform
disease of North American mule deer and elk) is not used in
animal or human food. However, there is no evidence to suggest
that CWD in deer and elk can be transmitted to humans.
- No infectivity has yet been detected in skeletal muscle
tissue. For one's own peace of mind, nervous and lymphatic
tissues from animals suspected of having BSE, should be removed.
(Sources: www.whyfiles.com;
www.cnn.com)
More Articles:
Vol. 3 No. 1
January-March 2001
»»
P15M high impact projects approved for livestock and poultry RDE network
»» Montemayor
bans UK meat imports
»» LDPs of
the DA: an analysis
»» Renewed
role of orivate sector valuable in livestock R&D - study reveals
»» Botanicals
effective against ectoparasites
»» Trichantera:
cheaper feed substitute to soybean oil meal
»» ELISA effective
in FMD diagnosis
»» National
integrated RDE agenda and program for livestock and fisheries
»» Mad cow
disease: know the risks
»»
The livestock and poultry industry: an overview
»» Scientists
find twinning technology in dairy cattle successful
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