London,
England (1/16/99)- A new medical diagnostic test will for the first time
allow quick identification of a rare but devastating form of neurologic disease
transmitted from cattle to humans. Until now, researchers have been hampered
in their efforts to trace cases of "mad cow disease' in humans by the
lack of a reliable test.
Bovine spongiform encephalopathy (BSE), also known as the mad cow disease,
is a progressive, lethal central nervous system disease of cattle. The brains
of afflicted animals develop vacuoles, clear holes that give the brain a spongy
appearance. Panic broke out in England in early 1996 when it appeared that
BSE had jumped to humans. The human manifestation of the bovine disease bears
a close resemblance to a rare disease known as Creutzfeldt-Jakob disease.
Both diseases are associated with the presence of proteins called prions that
appear to destroy brain and nervous tissue.
The new test requires a minor operation to obtain a specimen of tonsil tissue.
The antibody based test is specific for an abnormal form of protease-resistant
prion protein (PrPSc). Until the arrival of this test, the only way to ascertain
CJD infection was autopsy. For reasons unknown, the protein sought by the
test is only present in the tonsils of patients with the human form of BSE,
not in the tonsils of patients with the rare inherited form of the disease.
In addition to its clinical utility, the test should also advance research
in the field of prion diseases. The new test could help researchers estimate
the prevalence of vCJD infection in target populations. Researchers are also
very anxious to explore why the prion appears in the tonsils of patients with
one variant of the disease, but not another. The answers to this question
could provide a better understanding of how vCJD is transmitted. In the meanwhile,
the finding is likely to lead to more careful handling of tonsil and brain
tissue by health care workers.
"This new test has already proven very helpful in the diagnosis of new variant
CJD. While unfortunately, we have at present no means to treat this dreadful
disease, we can at least now provide a definite diagnosis at an earlier stage.
Research must continue apace to fully understand the disease and to develop
an effective treatment. This will at best take some years. The development
of a test which works on a simple blood sample remains an important goal,"
said Professor John Collinge Professor Collinge, Principal Research Fellow
of the Wellcome Trust and Director of the Medical Research Council Prion Unit.
The researchers remain concerned that a "substantial epidemic"
of vCJD could occur. The extremely long incubation period of the prions in
brain tissue means it may be decades before the full extent of vCJD in the
population is known.
Prion
diseases are associated with an accumulation of an abnormal form of the PrPSc
protein. Prions replicate in the lymphoreticular tissues (tissues of the immune
system) of the body, including the tonsils, before invading the central nervous
system. Researchers have not dtermined how BSE infects humans.
Graphic: Close-up
of Prion Particles in Brain Tissue click
to enlarge.
The research appears in the journal Lancet
(Volume 353, 9148 - Saturday 16 Jan, 1999).
Copyright
1999© Info
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