Mad Cow Disease
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Creutzfeldt-Jakob disease (CJD) is a rare, degenerative, invariably fatal
brain disorder. It affects about one person in every one million people
per year worldwide; in the United States there are about 200 cases per year.
CJD usually appears in later life and runs a rapid course. Typically, onset
of symptoms occurs about age 60, and about 90 percent of patients die within
1 year. In the early stages of disease, patients may have failing memory,
behavioral changes, lack of coordination and visual disturbances. As the
illness progresses, mental deterioration becomes pronounced and involuntary
movements, blindness, weakness of extremities, and coma may occur.
There are three major categories of CJD:
- In sporadic CJD, the disease appears even though the person has no known
risk factors for the disease. This is by far the most common type of CJD and
accounts for at least 85 percent of cases.
- In hereditary CJD, the person has a family history of the disease and/or
tests positive for a genetic mutation associated with CJD. About 5 to 10 percent
of cases of CJD in the United States are hereditary.
- In acquired CJD, the disease is transmitted by exposure to brain or nervous
system tissue, usually through certain medical procedures. There is no evidence
that CJD is contagious through casual contact with a CJD patient. Since CJD
was first described in 1920, fewer than 1 percent of cases have been acquired
CJD.
CJD belongs to a family of human and animal diseases known as the transmissible
spongiform encephalopathies (TSEs). Spongiform refers to the characteristic
appearance of infected brains, which become filled with holes until they
resemble sponges under a microscope. CJD is the most common of the known
human TSEs. Other human TSEs include kuru, fatal familial insomnia (FFI),
and Gerstmann-Straussler-Scheinker disease (GSS). Kuru was identified in
people of an isolated tribe in Papua New Guinea and has now almost disappeared.
FFI and GSS are extremely rare hereditary diseases, found in just a few
families around the world. Other TSEs are found in specific kinds of animals.
These include bovine spongiform encephalopathy (BSE), which is found in
cows and is often referred to as gmad cowh disease; scrapie, which affects
sheep and goats; mink encephalopathy; and feline encephalopathy. Similar
diseases have occurred in elk, deer, and exotic zoo animals.
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CJD is characterized by rapidly progressive dementia. Initially, patients
experience problems with muscular coordination; personality changes, including
impaired memory, judgment, and thinking; and impaired vision. People with
the disease also may experience insomnia, depression, or unusual sensations.
CJD does not cause a fever or other flu-like symptoms. As the illness progresses,
the patientsf mental impairment becomes severe. They often develop involuntary
muscle jerks called myoclonus, and they may go blind. They eventually lose
the ability to move and speak and enter a coma. Pneumonia and other infections
often occur in these patients and can lead to death.
There are several known variants of CJD. These variants differ somewhat
in the symptoms and course of the disease. For example, a variant form of
the disease-called new variant or variant (nv-CJD, v-CJD), described in
Great Britain and France-begins primarily with psychiatric symptoms, affects
younger patients than other types of CJD, and has a longer than usual duration
from onset of symptoms to death. Another variant, called the panencephalopathic
form, occurs primarily in Japan and has a relatively long course, with symptoms
often progressing for several years. Scientists are trying to learn what
causes these variations in the symptoms and course of the disease.
Some symptoms of CJD can be similar to symptoms of other progressive neurological
disorders, such as Alzheimerfs or Huntingtonfs disease. However, CJD causes
unique changes in brain tissue which can be seen at autopsy. It also tends
to cause more rapid deterioration of a personfs abilities than Alzheimerfs
disease or most other types of dementia.
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There is currently no single diagnostic test for CJD. When a doctor suspects
CJD, the first concern is to rule out treatable forms of dementia such as
encephalitis (inflammation of the brain) or chronic meningitis. A neurological
examination will be performed and the doctor may seek consultation with
other physicians. Standard diagnostic tests will include a spinal tap to
rule out more common causes of dementia and an electroencephalogram (EEG)
to record the brainfs electrical pattern, which can be particularly valuable
because it shows a specific type of abnormality in CJD. Computerized tomography
of the brain can help rule out the possibility that the symptoms result
from other problems such as stroke or a brain tumor. Magnetic resonance
imaging (MRI) brain scans also can reveal characteristic patterns of brain
degeneration that can help diagnose CJD.
The only way to confirm a diagnosis of CJD is by brain biopsy or autopsy.
In a brain biopsy, a neurosurgeon removes a small piece of tissue from the
patientfs brain so that it can be examined by a neuropathologist. This procedure
may be dangerous for the patient, and the operation does not always obtain
tissue from the affected part of the brain. Because a correct diagnosis
of CJD does not help the patient, a brain biopsy is discouraged unless it
is needed to rule out a treatable disorder. In an autopsy, the whole brain
is examined after death. Both brain biopsy and autopsy pose a small, but
definite, risk that the surgeon or others who handle the brain tissue may
become accidentally infected by self-inoculation. Special surgical and disinfection
procedures can minimize this risk. A fact sheet with guidance on these procedures
is available from the NINDS and the World Health Organization.
Scientists are working to develop laboratory tests for CJD. One such test,
developed at NINDS, is performed on a personfs cerebrospinal fluid and detects
a protein marker that indicates neuronal degeneration. This can help diagnose
CJD in people who already show the clinical symptoms of the disease. This
test is much easier and safer than a brain biopsy. The false positive rate
is about 5 to 10 percent. Scientists are working to develop this test for
use in commercial laboratories. They are also working to develop other tests
for this disorder.
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There is no treatment that can cure or control CJD. Researchers have tested
many drugs, including amantadine, steroids, interferon, acyclovir, antiviral
agents, and antibiotics. Studies of a variety of other drugs are now in
progress. However, so far none of these treatments has shown any consistent
benefit in humans.
Current treatment for CJD is aimed at alleviating symptoms and making the
patient as comfortable as possible. Opiate drugs can help relieve pain if
it occurs, and the drugs clonazepam and sodium valproate may help relieve
myoclonus. During later stages of the disease, changing the personfs position
frequently can keep him or her comfortable and helps prevent bedsores. A
catheter can be used to drain urine if the patient cannot control bladder
function, and intravenous fluids and artificial feeding also may be used.
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Some researchers believe an unusual "slow virus" or another organism causes
CJD. However, they have never been able to isolate a virus or other organism
in people with the disease. Furthermore, the agent that causes CJD has several
characteristics that are unusual for known organisms such as viruses and
bacteria. It is difficult to kill, it does not appear to contain any genetic
information in the form of nucleic acids (DNA or RNA), and it usually has
a long incubation period before symptoms appear. In some cases, the incubation
period may be as long as 40 years. The leading scientific theory at this
time maintains that CJD and the other TSEs are caused by a type of protein
called a prion.
Prion proteins occur in both a normal form, which is a harmless protein
found in the bodyfs cells, and in an infectious form, which causes disease.
The harmless and infectious forms of the prion protein have the same sequence
of amino acids (the "building blocks" of proteins) but the infectious form
of the protein takes a different folded shape than the normal protein. Sporadic
CJD may develop because some of a personfs normal prions spontaneously change
into the infectious form of the protein and then alter the prions in other
cells in a chain reaction.
Once they appear, abnormal prion proteins aggregate, or clump together.
Investigators think these protein aggregates may lead to the neuron loss
and other brain damage seen in CJD. However, they do not know exactly how
this damage occurs.
About 5 to 10 percent of all CJD cases are inherited. These cases arise
from a mutation, or change, in the gene that controls formation of the normal
prion protein. While prions themselves do not contain genetic information
and do not require genes to reproduce themselves, infectious prions can
arise if a mutation occurs in the gene for the bodyfs normal prion protein.
If the prion protein gene is altered in a personfs sperm or egg cells, the
mutation can be transmitted to the personfs offspring. Several different
mutations in the prion gene have been identified. The particular mutation
found in each family affects how frequently the disease appears and what
symptoms are most noticeable. However, not all people with mutations in
the prion protein gene develop CJD.
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CJD cannot be transmitted through the air or through touching or most other
forms of casual contact. Spouses and other household members of sporadic
CJD patients have no higher risk of contracting the disease than the general
population. However, exposure to brain tissue and spinal cord fluid from
infected patients should be avoided to prevent transmission of the disease
through these materials.
In some cases, CJD has spread to other people from grafts of dura mater
(a tissue that covers the brain), transplanted corneas, implantation of
inadequately sterilized electrodes in the brain, and injections of contaminated
pituitary growth hormone derived from human pituitary glands taken from
cadavers. Doctors call these cases that are linked to medical procedures
iatrogenic cases. Since 1985, all human growth hormone used in
the United States has been synthesized by recombinant DNA procedures, which
eliminates the risk of transmitting CJD by this route.
The appearance of the new variant of CJD (nv-CJD or v-CJD) in several younger
than average people in Great Britain and France has led to concern that
BSE may be transmitted to humans through consumption of contaminated beef.
Although laboratory tests have shown a strong similarity between the prions
causing BSE and v-CJD, there is no direct proof to support this theory.
Many people are concerned that it may be possible to transmit CJD through
blood and related blood products such as plasma. Some animal studies suggest
that contaminated blood and related products may transmit the disease, although
this has never been shown in humans. If there are infectious agents in these
fluids, they are probably in very low concentrations. Scientists do not
know how many abnormal prions a person must receive before he or she develops
CJD, so they do not know whether these fluids are potentially infectious
or not. They do know that, even though millions of people receive blood
transfusions each year, there are no reported cases of someone contracting
CJD from a transfusion. Even among people with hemophilia, who sometimes
receive blood plasma concentrated from thousands of donors, there are no
reported cases of CJD.
While there is no evidence that blood from people with sporadic CJD is
infectious, studies have found that infectious prions from BSE and vCJD
may accumulate in the lymph nodes (which produce white blood cells), the
spleen, and the tonsils. These findings suggest that blood transfusions
from people with vCJD might transmit the disease. The possibility that blood
from people with vCJD may be infectious has led to a policy preventing people
in the United States from donating blood if they have resided for more than
3 months in a country or countries where BSE is common.
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To reduce the already very low risk of CJD transmission from one person
to another, people should never donate blood, tissues, or organs if they
have suspected or confirmed CJD, or if they are at increased risk because
of a family history of the disease, a dura mater graft, or other factor.
Normal sterilization procedures such as cooking, washing, and boiling do
not destroy prions. Caregivers, health care workers, and undertakers should
take the following precautions when they are working with a person with
CJD:
- Wash hands and exposed skin before eating, drinking, or smoking.
- Cover cuts and abrasions with waterproof dressings.
- Wear surgical gloves when handling a patient's tissues and fluids or dressing
the patient's wounds.
- Avoid cutting or sticking themselves with instruments contaminated by the
patient's blood or other tissues.
- Use disposable bedclothes and other cloth for contact with the patient.
If disposable materials are not available, regular cloth should be soaked
in undiluted chlorine bleach for an hour or more, then washed in a normal
fashion after each use.
- Use face protection if there is a risk of splashing contaminated material
such as blood or cerebrospinal fluid.
- Soak instruments that have come in contact with the patient in undiluted
chlorine bleach for an hour or more, then use an autoclave (pressure cooker)
to sterilize them in distilled water for at least one hour at 132 - 134 degrees
Centigrade.
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Many researchers are studying CJD. They are examining whether the transmissible
agent is, in fact, a prion or a product of the infection, and are trying
to discover factors that influence prion infectivity and how the disorder
damages the brain. Using rodent models of the disease and brain tissue from
autopsies, they are also trying to identify factors that influence susceptibility
to the disease and that govern when in life the disease appears. They hope
to use this knowledge to develop improved tests for CJD and to learn what
changes ultimately kill the neurons so that effective treatments can be
developed.
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Creutzfeldt-Jakob
(CJD) Foundation Inc.
National Organization
for Rare Disorders (NORD)
Alzheimer's Association
Alzheimer's Disease
Education and Referral Center (ADEAR)
National Hospice and Palliative
Care Organization /Natl. Hospice Foundation
National Family Caregivers
Association
Family Caregiver Alliance
Well Spouse Foundation
Centers for Disease Control
and Prevention (CDCP)
Food and Drug Administration
(FDA)
World Health Organization
Brain Resources and Information
Network(BRAIN)
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