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XMRV and the Canadian Blood Supply
By: Dana V. Devine, Ph.D., Vice
President,
Medical, Scientific & Research Affairs, Canadian Blood
Services
QUEST 82, Winter 2009/10.
Canadian Blood Services takes the safety of the blood supply
very seriously. We remain focused on the identification of potential
threats to the blood supply whether they are blood borne pathogens or
issues that may jeopardize the sufficiency of the supply of blood and blood
products needed by patients.Last fall, a report was published in the
medical literature which suggested that there was an association between
chronic fatigue syndrome and the presence of a virus called xenotropic
murine leukemia virus-related virus (XMRV). Lombardi and co-workers
found that there was not only evidence of the genetic material of this virus
in blood samples from American CFS patients, it was much more common
than in samples from healthy individuals, 67% in CFS patients versus 4% in
healthy people. Furthermore, these researchers could show that the
virus from patient blood samples was able to infect cultured cell lines in
the laboratory. What remained unknown was whether this virus was
actually the cause of CFS.It was also unclear from this study whether
there was actually live virus in healthy people as these researchers
were only able to demonstrate a piece of the XMRV genome called 'gag'
but not other parts of the virus that one would expect to find if the virus
was intact and capable of being infectious. So, important questions
remained unanswered, particularly with respect to risk to the blood
system. Nevertheless, the information was sufficiently important that
Canadian Blood Services along with its sister organizations in the United
States began to determine what should be done about protecting the blood
supply while other researchers work to confirm whether the Lombardi findings
can be reproduced.There are no fewer than four different groups of
people representing a wide variety of researchers from both the transfusion
medicine community and from the public health community working together
to understand the significance of XMRV to the blood supply. One of the
first steps was the recognition that we lack a proper test to look for
XMRV because the virus is quite new and there has not yet been any clinical
demand to test for it outside of highly specialized research
laboratories.In order to have confidence in a blood screening
test, we must know that it has a high level of sensitivity, that is, it is
good at finding a particular virus, while at the same time it needs to
have a high level of specificity, meaning that if it is positive, the
particular virus is present. So, the development of XMRV tests that
allow us to confidently identify the virus is a critical first step.
The second step will be to test enough of the North American blood donor
base to be able to understand whether XMRV actually is carried by healthy
blood donors.It is an integral part of the scientific discovery
process that new findings must be confirmed by other researchers working
independently from those who reported the initial observation. Although
science is never completely free of bias, this process has evolved as an
effective way for scientists to determine whether or not a new discovery is
'true'. The publication of discoveries in the medical literature uses
a somewhat proscribed format to describe what the study design was, how it
was conducted, what the results were, any problems or pitfalls with the
research and what the research might mean.In early January, 2010, a
second report looking for XMRV in CFS patients appeared in the medical
literature. This study, conducted in the United Kingdom, used samples
from an even larger group of CFS patients with strong symptoms. Although
the study appears to have been conducted with appropriate scientific
rigour, these investigators were unable to confirm the findings of the
American study. They found only a single CFS patient with evidence of
XMRV in their large cohort. So, we are left with a common scientific
conundrum - uncertainty over whether research findings are correct or not.
Is XMRV a virus that is more common in North America than on other
continents? If these CFS patients in the UK do not have XMRV, does that
rule out XMRV as a cause of CFS, or not? More studies will be required
before we know how this issue will play out.So what will Canadian Blood
Services do in the meantime? At the present time, we have accepted
blood donations from donors who report a history of CFS but are now
well. Donors who are not well may not donate blood. Given the lack of
clarity around XMRV, we are changing the way we manage donors such that
any donor who has a medical history of CFS will be indefinitely deferred
from donating blood. Once we understand more about the possible role of
XMRV in the etiology of CFS, we will revisit this decision to determine
whether the indefinite deferral is still warranted.XMRV represents a
single agent that raises concerns about blood safety, but it is not alone
on the list of potential risks to blood safety. Canadian Blood Services
monitors the current state of the science as well as the movement around
the globe of a series of pathogenic agents that are known to be
transmissible in blood. These include well known agents such as the
dengue fever virus, and relative newcomers such as the Chikungunya
virus. There are literally dozens of agents which present some level
of risk, however, as long as the risk is actively managed, harm to
patients can be avoided. At the present time, we either ask risk-based
questions to defer donors or we implement blood screening tests where it
makes sense to do so. However, going forward, Canadian Blood Services is
working toward the implementation of a relatively new technology called
pathogen inactivation which is a broad-spectrum treatment to kill all kinds
of pathogens in fresh blood products.At the present time, systems
are in the marketplace that can be used to treat platelet products and
plasma products and researchers are actively working to develop processes
that can be used for red blood cells. This technology will allow
Canadian Blood Services to proactively protect the blood system from
pathogenic agents. While systems are not yet here that can be used to
treat the full blood supply, even partial treatment will afford an increased
level of protection from known as well as emerging pathogens. |
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