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From: TSS ()
Date: July 14, 2007 at 9:21 am PST


11. When considering how the level of infectivity may change over the
course of the incubation period SEAC concluded (see Annex 1)
that “the available data show that blood is infectious during the
preclinical stage of vCJD. Although the precise time in the
incubation period of vCJD at which blood becomes infectious is
unclear, data from animal models suggest it may be infectious from
at least, if not before, the middle of the incubation period.” This
7 Donnelly et al. (2002) Implications of BSE infection screening data for the scale of the British
BSE epidemic and current European infection levels. Proc. R. Soc. Lond. B. 269, 2179-2190.
© SEAC 2007
conclusion is largely based on unpublished experiments8 that
examined infectivity in the blood of hamsters at around half and
three quarters of the way through the incubation period and at
clinical stage of disease following intracerebral or oral inoculation
with hamster scrapie. Infectivity was first detected at the mid-point
of the incubation period with the level of infectivity increasing
relatively linearly towards the clinical stage of infection.
Extrapolation of these data suggested infectivity could have first
appeared in blood at around a third of the way into the incubation
period (see Annex 1).
12. The mean incubation period for primary vCJD is uncertain. Two
estimates of the mean incubation period for primary vCJD from
analyses based on clinical vCJD case data both suggest it may be
around 12.6 years (95% confidence intervals of 8 – 359 and 10.5 -
14.7 years10) for the MM genotype (see Annex 3). Given the lack
of clinical vCJD cases of the MV or VV genotype observed to date,
the mean incubation period of primary vCJD in these genotypes
must be longer than that of the MM genotype.
13. Given the estimated incubation period and an assumption that
vCJD infectivity does not appreciably accumulate in blood during
the first third of the incubation period, it may be reasonable to
assume that plasma from a large proportion blood donors infected
with primary vCJD may not be infectious for several years following
14. If the assumptions above about dietary BSE exposure and/or the
accumulation of vCJD infectivity in blood are accepted, the start of
the period of greatest/appreciable risk of infection from UK sourced
plasma derivatives could be significantly narrowed. This could
allow a re-assessment by DH of exposure to potentially
contaminated plasma derivatives.

8 Unpublished data from the VA Medical Center, University of Maryland, Baltimore, USA
presented by Dr R Rohwer.
9 Ghani et al. (2003) Updated projections of future vCJD deaths in the UK. BMC Infect.
Disease. 3, 4-11.
10 Boelle et al. (2004) Epidemiological evidence of higher susceptibility to VCJD in the young.
BMC Infect. Disease. 4, 26-32.


11. The available data show that blood is infectious during the preclinical stage
of vCJD. Although the precise time in the incubation period of vCJD at
which blood becomes infectious is unclear, data from animal models
suggests it may be infectious from at least, if not before, the middle of the
incubation period. The source of infectivity in blood is not understood. Data
from rodent studies suggests that infectivity in whole blood is around 10
ID/mL and that it mostly resides in the plasma and white blood cell
components with infectivity associated with white blood cells substantially
depleted by extensive washing. However, additional information from other
animal models is required to assess whether these findings may be closely
representative of vCJD infectivity in human blood. It is clear that an
infectious dose in blood can be disseminated but not diluted by distribution
to a large number of recipients. Consequently, pooling of potentially
infectious material, or in other ways disseminating infectious material
between a number of recipients, will not reduce the number of people
infected, and is likely to increase the number of people infected.

July 2006


Risk of vCJD Transmission from UK-derived Plasma Derivatives:
the case for a reassessment of infectivity assumptions
Dr Peter Bennett
Health Protection Analytical Team
Department of Health
27th April 2007
The following note for SEAC 97 sets out the case for a reassessment of the vCJD
infectivity likely to be contained in plasma derivatives sourced from an infected
donor. If this case is accepted, it is requested that SEAC carry out such a
reassessment at its next meeting (SEAC 98 on 20.07.2007)
DH Risk Assessments for vCJD transmission via blood and blood products (plasma
derivatives) have considered a wide range of assumptions, but have until recently
made use of scenarios for infectivity suggested in work commissioned from DNV
(1999, 2003) which summarised existing research on animal models.
For blood components (red cells, platelets, fresh frozen plasma), revised infectivity
scenarios are now available, based on new evidence discussed by SEAC in 2006. It is
not suggested that these be re-examined at this stage.
However, assumptions for plasma derivatives - e.g. Factor XIII or albumin - were not
formally reconsidered in 2006. Furthermore, the UK risk assessment is based on more
pessimistic scenarios than those used in other countries. This has had a significant
impact on risk management, via highly “precautionary” recommendations of CJDIP.
(By contrast, here is much less international variation with regard to the potential risks
from receipt of infected blood components.)
The time at which infectivity would appear in blood, within an infected donor’s
incubation period is relevant, as well as the level of infectivity present. To date, risk
management has been based on the precautionary assumption of infectivity being
present throughout the incubation period, though there is some evidence to suggest a
delay. A change in this assumption could have implications both for recipients of
plasma derivatives and for other “at risk” groups.

snip...see full text ;

From: "Terry S. Singeltary Sr." <[log in to unmask]>
Subject: Potential Risk of vCJD From Plasma-Derived Products FDA

By Terry S Singeltary


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