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From: TSS ()
Subject: EARLY PHASE OF vCJD INFECTION IN BLOOD TRANSFUSION POSITION STATEMENT
Date: May 27, 2005 at 6:39 am PST

##################### Bovine Spongiform Encephalopathy #####################

1

POSITION STATEMENT

EARLY PHASE OF vCJD INFECTION IN BLOOD TRANSFUSION

RECIPIENTS

Issue

1. The Committee on Microbiological Safety of Blood, Tissue and

Organs has requested advice from SEAC on whether a scientific

distinction can be drawn between historic and recent blood

transfusion recipients in terms of the relative load of the vCJD

agent that may be present in the bone, tissues or organs of the

blood transfusion recipient. In the context of this question, a recent

recipient is defined as having received a blood transfusion within

the week prior to bone, tissue or organ donation. A historic

recipient is defined as having received a blood transfusion in the

more distant past.

Background

2. A pre-symptomatic diagnostic test for vCJD is currently not

available. Therefore, blood, bone, tissue or organ donors with a

sub- or pre-clinical vCJD infection cannot be identified prior to

donation. Two cases of vCJD infection in recipients of blood from

donors that subsequently developed vCJD suggest that the

disease may be transmitted from asymptomatic individuals via

blood transfusion. Epidemiological evidence of iatrogenic

transmission of sCJD suggests there is a potential risk of vCJD

transmission via tissue/organ transplantation.

3. There are no data on the tissue distribution of vCJD infectivity in

humans in the first week following infection by blood transfusion.

There is some, albeit very limited, information from mouse studies

on prion replication and spread in the early phase of infection.

However, these studies used inocula, routes of administration and

prion strains not directly applicable to the human blood transfusion

situation.

2

Early phase tissue accumulation of abnormal prions

4. On the basis of the very limited information available, it is

considered unlikely that significant prion replication would occur in

tissues in the first week following transfusion with infected blood.

Thus, the level of abnormal prions accumulating in a tissue would

probably correlate with the level of vascularisation of that tissue.

Highly vascularised organs such as the liver, lung and spleen, as

well as bone, would be more likely to contain the agent compared

with other organs. At later times in the incubation period (likely to

be well in excess of one week), the accumulation of abnormal prion

protein and infectivity would be expected to correlate with the

ability of various tissues to support prion replication, with the

central nervous system containing the highest levels of infectivity.

Relative risks

5. Data are too limited to allow quantification of the risks of transplant

associated vCJD transmission from donors that have received a

blood transfusion.

6. The number of pre- and sub-clinical vCJD infections in the

population is believed to be small. Therefore, there is a small risk

of vCJD transmission from transplantation of tissues/organs from

all donors, irrespective of whether they have received a blood

transfusion prior to donation. The additional risk resulting from a

tissue/organ donor having received a blood transfusion at any time

prior to donation is likely to be small. Furthermore, the introduction

of precautionary safety measures to protect the blood supply, such

as leucodepletion and exclusion of previously transfused blood

donors, means that, in general, the risk of blood transfusionassociated

transmission of vCJD from tissue/organ donation is, if

anything, likely to be lower if the transfusion is recent rather than

historic. However, it is not possible to define a threshold of lowest

risk in terms of a specific date of, or period of time following, a

blood transfusion.

Possible risk reduction measures

7. Screening cadaveric donors for markers of infection would allow,

depending on the sensitivity of the test used, pre- or sub-clinically

infected donors to be identified prior to the use of the donated

tissues/organs. Retrospective screening of donors would also help

to inform assessment of transmission risks.

3

8. On the basis that tissue/organ infectivity levels in the very early

stage of infection are associated with the blood content of

tissues/organs, washing or perfusing tissues to remove blood could

reduce the infectious load. In this respect, it would be important to

consider processes that efficiently remove bone marrow and blood

from bone.

9. Avoiding the pooling of tissues from different donors to be

transplanted into one individual reduces transmission risks to that

individual.

Summary

10. There is no clinical evidence that vCJD has been transmitted

through tissue/organ transplantation. However, a potential risk of

transmission via this route exists. Relevant data are extremely

limited but suggest that in the early phase of infection, significant

prion replication is unlikely to occur and that, therefore, tissue

levels of abnormal prions following recent transfusions are likely to

be related to the blood supply to each specific tissue.

11. A risk of transplant associated transmission of vCJD exists from

tissue/organ donors that have not received blood transfusions.

The additional risk as a result of a donor having received a recent

blood transfusion is likely to be very small. Post mortem

assessment of donor infection would provide the best method of

risk reduction and enable these risks to be quantified.

12. In assessing and communicating the risks a balance must be

struck between the small risk of vCJD transmission by

transplantation and the benefits to patients receiving a transplant,

especially where tissues/organs are scarce and are required for

(potentially) life-saving procedures.

SEAC

May 2005

http://www.seac.gov.uk/pdf/cjd.pdf

TSS

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