From sheep to cattle and then to human beings, spongiform encephalopathies, a group of fatal brain maladies, have caught the attention of scientists who are now busy finding the missing links
WITH the fallout of the mad cow
disease in Britain, attention has been
drawn to its human counterpart -
Crc utzfeldt- Jakob disease (CM).
Reported simultaneously in 1921 by
two independent scientists, Hans
G Creutzfeldt and Alfons Jakob, the
disease affects the brain.
Normally the disease strikes those
who are in their '50s and '60s. The
renewed interest has re 'sulted from conclusions derived by a British team of
experts who have identified a cluster of
10 cases of a variant form of the disease
which affects people younger than 42
years of age and some even in their
teens. An infection similar to QD exists
in cattle. Called bovine spongiform
encephalopathy (BSE), the infection was
found in 150,000 British animals
between 1986 and 1995. The disease
apparently entered cattle from feed containing bone meal and offal from sheep
afflicted with a closely related infection
called scrapie. A satisfactory explanation
for the crossing of the species barrier
and as to how human beings got the disease is yet to be established.
All the 10 victims had abnormalities
called 'PrP plagues' in their brain tissue.
The plagues have been seen in scrapie
and in a QD-like disease called kuru,
found only'in New Guinean tribesfolk
who consume human brain in mourning rituals. The plagues had not been
seen in CJD, however.
Researchers are trying to establish
the role of diet and environment in the
development Of QD, after noting its tentative linkage to mad cow disease.
According to Robert G Will and his colleagues of the national QD surveillance
unit in Edinburgh, Scotland, UK, "That
it is due to exposure to the BSE agent is
perhaps the most plausible interpretation of our findings. However, we
emphasise that we do not have
direct evidence of such a link and other
explanations are possible."
There have been 62 reported cases of
spongiform encephalopathies directly
related to growth hormone injections,
worldwide. This hormone is derived
from the pituitary gland of human
cadavers and then injected into the
patient undergoing treatment. Sixteen
cases have been identified out of 6,200
patients who had taken the injection
distributed by the National Institutes of
Health in us. The long incubation suggests that the disease may grow with
time. Some cases have been the result of
reuse of chemically disinfected electrodes which are implanted to study
brain wave patterns of patients with
such diseases. There have also been
cases where a person has got the infection after surgery. But in all cases, some
part of the brain or the central nervous
system has been involved.
The disease could also be passed on
from parents to children. This conclusion is drawn from the fact that there are
certain communities in the world more
susceptible to it than others. These
account for 10 per cent of all cases the
world over.
Today, it is believed that rogue
prion proteins, which are abnormal
variants of prion proteins, are the cause
of spongiform diseases. The disease-
causing prions are believed to convert
the normal prions into their abnormal
form. The function of normal prion
protein which is produced by a widely
occurring gene, is not known, but they
lack any hereditary materials like the
RNA and DNA. It was this factor which led
many scientists to ridicule the prion theory proposed by Stanley B Prusiner of
the University of California at San
Francisco, us. Regarding it as heretical,
scientists could not believe that the disease could be transmitted from one generation to the next without the involvement of genetic material.
However, many scientists are
now convinced of this theory as some
partial evidence has been furnished
thiough experiments. Laboratory
animals infected with prions developed
spongiform disease, while those in
which prions were destroyed and then
injected did not.
Agents causing spongiform diseases
are not guided by any preset pattern.
They do not get any reaction from the
body's immune system which is otherwise very prompt in warding off foreign
particles. One known difference
between agents which cause spongiform
disease and those that cause other common infections is that the former are
resistant to beat, uv light, radiation and
many chemical disinfectants. This gives
no guarantee that the extant food
processing technologies like cooking,
pasteurisation, sterilisation, freezing,
drying and pickling are foolproof
against a spongiform agent present in
foodstuffs.
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