Risk of Transmission of Prion Diseases by Blood
Transfusion
Upgraded
--------------------------------------------------------------------
Scientists
[now] say there is "an appreciable risk" of people [contracting]
the human
form of BSE (bovine spongiform encephalopathy) through blood
transfusions, a
significant upgrading of the threat posed by the inevitably
fatal disease
[variant Creutzfeldt-Jakob disease, abbreviated as vCJD or CJD
(new var.) in
ProMed-mail]. The results from tests on sheep suggest that the
danger is far
more serious than first suspected. Previously the risk has
been described by
the government as "theoretical".
One in six [of 24] animals given blood
from infected sheep appear to have
[contracted] disease so far [two of
6 sheep had received blood containing
BSE prions and 4 had received scrapie
prions. - Mod.CP]. The experiments by
scientists at the Institute of Animal
Health indicate that more blood
components than previously thought might
carry the agents of BSE or vCJD,
and blood might be infective long before
animals, and by extension humans,
show outward signs of the long-incubating
diseases. The latest experiments
suggest that plasma and red cells might have
significant infectivity.
So far there is no evidence that anyone infected
with vCJD has passed it on
to others through transfusion; 22 people have
received donations from 8
people who later went down with the disease, and
although some of those have
died, vCJD was not considered a factor. At least
4 people with vCJD had
earlier had blood donations, but again transfusion has
not been considered a
factor.
The scientists who made the transfusion
of infected blood between sheep are
to report in [full in] the November issue
[see below] of the Journal of
General Virology (JGV) . They say another sheep
has gone down with BSE and 2
more are showing clinical signs of the disease.
If those cases are
confirmed, one in 6 of the 24 sheep transfused with either
whole blood or a
component will have succumbed through transfusion. [The
numbers in this
report are at variance with the information in the abstract
of the JGV paper
reproduced below. Previously transmission of BSE to a single
sheep had been
reported, and now a second animal shows signs of disease. In
addition
another 4 sheep appear to have contracted natural scrapie via
blood
transfusion. - Mod.CP]
The findings, circulated to blood
specialists, are regarded as enormously
significant. They have prompted
urgent consideration of new measures to
protect the public and orders to
hospitals to drastically reduce their use
of blood, including using
technology that allows the recycling of patients'
own blood. But the
Department of Health and blood transfusion services last
night appealed to
the public to continue donating blood. The national blood
service, which has
nearly 2 million donors in England and Wales, said: "We
still need to collect
about 10 000 units a day because there are people in
hospital who rely on
transfusions. We need to strike a balance between an
unknown risk and
maintaining sufficient supplies."
So far 115 Britons have died and 9
others are thought to be dying from vCJD,
for which the prime culprit still
appears to be contaminated meat eaten many
years ago. The government has
introduced precautionary measures over blood
but it considered the risk
theoretical even after autumn 2000, when
scientists in Edinburgh and Compton,
Berkshire, revealed that the blood from
a sheep fed cattle brain infected
with BSE had infected a previously healthy
animal.
All blood given to
humans has the white cells removed because they are
regarded as potentially
the most dangerous carriers of vCJD through
transfusion. Most plasma is
imported because of risks to haemophiliacs who
have a constant need for the
blood clotting factors.The government is
considering banning all people who
have ever received transfusions from
donating blood, a decision that might
remove one in 10 donors; importing
more plasma, particularly for transfusions
in babies and young children; and
forcing the removal of blood platelets from
plasma.
Expert advisers are expected to make recommendations within
weeks, but
importing red blood cells, most widely used to replace blood lost
in
surgery, would be impossible. They have a shelf life of 35 days and are
in
short supply around the world.
The possibility of a blood test for
vCJD next year, though essential for
public safety, might dissuade up to half
Britain's donors from offering
blood, because people would have to face [the
possibility of] being told
they have an incurable
disease.
--
ProMED-mail
<promed@promedmail.org>
[The
paper referred to above is entitled "Transmission of prion diseases by
blood
transfusion", contributed by Nora Hunter, James Foster, Angela
Chong,
Sandra McCutcheon, David Parnham, Samantha Eaton, Calum MacKenzie
& Fiona
Houston.
<http://www.socgenmicrobiol.org.uk/JGVDirect/18580/18580a.htm>
The
abstract of the paper reads as follows:
"Attempts to detect infectivity in
the blood of humans and animals affected
with transmissible spongiform
encephalopathies (TSEs or prion diseases) have
often been inconclusive
because of the limitations of cross-species
bioassays and the small volumes
of blood that can be injected by the
intracerebral route. A model has been
developed for the experimental study
of TSE transmission by blood transfusion
using sheep experimentally infected
with bovine spongiform encephalopathy
(BSE) or natural scrapie as donors and
susceptible scrapie-free sheep as
recipients. Donors and
recipients of the same species greatly increase the
sensitivity of the
bioassay and in sheep large volumes of blood can be
injected by the
intravenous (i.v.) route.
"Transmission of BSE to a
single animal using this approach was reported
recently. This study confirms
this result with a second transmission of BSE
and four new cases of
transmission of natural scrapie. Positive
transmissions occurred with blood
taken at pre-clinical and clinical stages
of infection. Initial studies
indicate that following
such infection by the i.v. route, deposition of the
abnormal prion protein
isoform, PrPSc, in peripheral tissues may be much more
limited than is seen
following oral infection.
"These results confirm
the risks of TSE infection via blood products and
suggest that the measures
taken to restrict the use of blood in the UK have
been fully justified." -
Mod.CP]
[I note that "Initial studies indicate that following such
infection by the
i.v. route, deposition of the abnormal prion protein
isoform, PrPSc, in
peripheral tissues may be much more limited than is seen
following oral
infection." This appears to suggest that while
blood-borne transmission can
occur, it is less likely to cause disease than
ingestion. - Mod.JW]
[see also:
CJD (new var.), blood donation
recipients - UK 20020131.3450
2001
----
CJD (new var.), blood donation
restrictions - USA 20010911.2186
CJD (new var.), blood supply at risk - UK
20010707.1304
CJD (new var.), blood supply collaboration 20010706.1294
CJD
(new var.), blood transfusion risk: update 20011217.3050
CJD (new var.),
cluster - UK (Leicestershire) (05) 20010322.0568
CJD (new var.), contam blood
prods exported - UK (02) 20010210.0278
CJD (new var.), contaminated blood
prods exported - UK 20010209.0267
2000
----
BSE, possibility of
blood-borne transmission
20000915.1587
BSE, possibility of blood-borne transmission (02)
20000918.1604
BSE, possibility of blood-borne transmission (03)
20000919.1614
CJD (new var.), blood donation -
Switzerland 20000229.0272
CJD (new
var.), blood donation restrictions - Canada
20000901.1468]
...............jw/cp/jw