BACKGROUND INFORMATION
Transmissible
spongiform encephalopathies or TSEs are a group of fatal, rare,
progressive neurological disorders that occur in humans and
animals. TSEs are also referred to as prion diseases. The word
prion is derived from the phrase proteinaceous infectious particle.
Prions occur in both a normal form, which is a harmless protein
that resides throughout the body, but have a higher concentration
in the brain and nerve tissue, and in infectious forms, which
cause disease. Prion disease is believed to result when normal
prion proteins fold into an abnormal shape capable of causing
other normal prions to misfold. The abnormal prion proteins
accumulate causing a spongy brain tissue degeneration resulting
in progressive dementia, visual and motor disturbances, difficulty
swallowing, behavioral changes, and death.
The most
common TSE affecting humans is Creutzfeldt-Jakob Disease (CJD).
CJD falls into 4 subtypes: sporadic (spontaneous), familial
(genetic/inherited), iatrogenic (inadvertent transmission via
medical/surgical procedure), and variant. Sporadic CJD
is not related to Mad Cow Disease.
Mad Cow
Disease is a bovine TSE known as Bovine Spongiform Encephalopathy
(BSE). The human acquired TSE linked to the ingestion of beef
from cows with BSE is a different clinical and pathological
disease known as variant CJD (vCJD).
Occurrence – CJD occurs worldwide with
an incidence ranging between 0.5 and 1.5 cases per million people
per year.
Sporadic
CJD (sCJD) accounts for greater than 85% of all CJD cases, familial
CJD accounts for 10-15% of all cases, and iatrogenic CJD accounts
for less than 5% of all CJD cases. vCJD is extremely rare. To
date, there have been 3 cases of vCJD in the United States,
two due to exposure in the United Kingdom and one due to exposure
from Saudi Arabia. There have not been any domestically acquired
vCJD cases in the United States.
Transmission –
• The mode of transmission for sporadic CJD is not known.
• Familial CJD is an inherited condition and is very rare.
• Iatrogenic CJD infection is inadvertently transmitted
usually from a person with sCJD to someone else in the course
of medical/surgical treatment through the use of instruments
in contact with infected brain issue or transplant of infected
tissue itself.
• Variant CJD, first recognized in the United Kingdom
in 1996, is associated with bovine spongiform encephalopathy
(BSE) or Mad Cow Disease. The exact route of transmission from
BSE to humans is unknown but is believed that vCJD in humans
results from the consumption of cattle products infected with
the BSE prion protein.
Communicability
– There is no evidence of person-to-person transmission
of either vCJD or sCJD by casual contact or by the airborne/respiratory
route. Central nervous system tissues are infectious
throughout symptomatic illness. Other tissues and CSF may also
be infectious. Infectivity during the incubation period is not
known, but animal studies suggest that lymphoid and other organs
are probably infectious before signs of illness appear. In very
rare circumstances, sCJD has been acquired by contaminated neurosurgical
instruments, transplantation of central nervous system tissue
(corneal grafts and dura mater grafts), peripheral administration
of human-derived pituitary hormones, and possibly for vCJD only,
in transfused blood.
For guidelines
on infection control practices see the following links:
http://www.cdc.gov/ncidod/dvrd/cjd/qa_cjd_infection_control.htm
http://www.who.int/csr/resources/publications/bse/WHO_CDS_CSR_APH_2000_3/en/
Incubation
Period - The incubation period for iatrogenic CJD varies
by route of exposure from 15 months to > 30 years. For vCJD
the incubation period is unknown but it is estimated to be 10
to 20+ years. Once symptoms begin, the disease is rapidly progressive
and usually results in death within months up to a maximum of
about 2 years.
Signs
and Symptoms - There are broad similarities between
all forms of CJD involving neurological and psychiatric problems
that get progressively worse. Typically patients have problems
with dementia that rapidly worsens as well as difficulties with
walking and movement. However, the precise symptoms and course
do differ between types of the disease.
The variant
form differs from the sporadic form of CJD in the age distribution
of affected patients, duration of illness, clinical manifestation
and course, as well as the pathologic lesions in the brain and
biochemical characteristics of the agent.
Symptoms
and type of disease
Sporadic
CJD – Is characterized by spontaneous onset of rapidly
progressive dementia; sudden, involuntary jerking of a muscle
or group of muscles (myoclonus); visual disturbance; tremors;
rigidity; balance and difficulties with coordination; spasticity;
inability to speak (akinetic mutism). The disease course is
rapid and death typically occurs within 6 months after disease
onset. Age at onset in sCJD cases is usually greater than 60
years of age.
Familial
CJD –. In general the symptoms of the familial form
of CJD are similar to those of sporadic CJD. Often familial
CJD is diagnosed at an earlier age (around 50 years of age),
has a later onset of dementia and a longer course of illness
(6 to 36 months) than is typical for sCJD. DNA analysis on blood
or brain tissue can be done to test for the presence of a genetic
mutation. This test can only determine if a case has a familial
prion disease. The National Prion Disease Pathology Surveillance
Center (NPDPSC) does genetic testing for fCJD.
Variant
CJD - Usually afflicts younger people (onset is usually
in people less than 55 years of age) and has a longer duration
of illness (median duration of 12-14 months). Symptoms of vCJD
are typically characterized as psychiatric or behavioral changes
(psychosis, depression, anxiety, agitation, auditory or visual
hallucinations); sensory pain in the extremities or other areas
not related to injury or stimulation; lack of coordination and
involuntary movements; and progressive dementia.
Treatment - There is currently no established
treatment to prevent sporadic or familial CJD or cure any form
of CJD. There are medications that may relieve symptoms and
make the patient more comfortable. The current treatments are
supportive. The only clinical trial for treatment of CJD is
occurring at the University of California, San Francisco (http://memory.ucsf.edu/cjd/livingwithcjd/clinicaltrials)
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