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November 28th, 2003

Experts offer cautious optimism on risk of vCJD transmission through plasma derivatives


Leading experts gathered last week in Scotlands´ capital city, Edinburgh for the 2nd International Scientific Workshop on TSE`s and the Safety of Blood and Plasma Products.

Organised by the European Plasma Fractionators Association (EPFA), the two day event attracted over 130 participants from 17 countries. Delegates including scientists, regulators, plasma fractionation industry representatives and patient advocacy groups heard and debated the latest research on transmissible spongiform encephalopathies (TSE´s).

TSEs are fatal brain diseases that include Creutzfeldt-Jakob Disease (in variant, sporadic and familial forms) of humans, scrapie in sheep, and BSE or “mad cow disease” of cattle. Infectivity is closely associated with abnormal prion proteins. Normal prion protein is found throughout the body but during TSE infections they change shape and accumulate in large deposits in the brain and nervous system. Damage from the infection causes sponge-like holes to appear in the brain during the late clinical stages of these fatal degenerative central nervous system disorders.

Although blood-borne TSE infectivity has been transmitted by transfusion in laboratory rodents infected with TSEs and in sheep, experimentally infected with BSE or naturally infected with scrapie, it is still not known if vCJD could be transmitted by either blood transfusion or plasma derivatives in humans.

Despite this uncertainty, there is mounting evidence to suggest that the risk may be purely hypothetical
  • There has been no transmission of either sCJD or vCJD in either monkeys or chimps inoculated (both iv and ic) with plasma, buffy coat or whole blood from infected animals;
  • The peak of the vCJD epidemic has occurred and the disease is now in decline. In total there have been 143 cases in the UK and a further 10 elsewhere (at least 3 of these were exposed to vCJD in the UK). Although the number of new cases rose exponentially from 1994, when the variant form of CJD was first recognised, through to 1999 there has been a downward trend in the last three years;
  • This has led to a revision in the maximum predicted number of cases from 13.7 million to <300;
  • There is convincing evidence from numerous fractionation industry partitioning experiments to demonstrate a very high capacity for prion reduction during the processing of plasma derivatives.
“The risk of blood-borne disease transmission from vCJD is not demonstrably greater than that from sporadic”
Prof Paul Brown- NIH
However, neither plasma manufacturers, nor the scientific, medical or patient communities can be complacent. As yet, there is neither treatment for vCJD, nor a method sensitive enough to detect infection from blood or during the early preclinical stage of infection. Further uncertainties exist for instance it is not known whether prevalence of infectivity would equate to prevalence of disease. Additionally, even if a donor diagnostic test was to become available there are a plethora of unresolved ethical implications involved in both testing and informing donors of their results, as well as a potential negative impact on the blood supply.

Despite the many unresolved issues, the overall message from the conference was one of cautious optimism.

This was in part supported by the updated results from the UK Post transfusion epidemiology study. This look-back type study is following the recipients who received transfusions from UK blood donors who were subsequently diagnosed with vCJD.

COMPONENTS TRANSFUSED
(from donors subsequently diagnosed with vCJD)
NUMBER
Red Blood Cells (RBC´s)
23
Buffy-coat depleted red blood cells
2
Fresh Frozen Plasma (FFP)
4
Whole blood
2
Cryo-depleted plasma
1
Cryoprecipitate
1
Units sent for plasma fractionation
8

Although 20 of the recipients have died, neurodegenerative disorder (vCJD) was not believed to be the cause of death in any case. The surviving 13 recipients have shown no signs of vCJD infection. Whilst these results are promising, it is still too early to state with absolute certainty that there is zero risk as only 2 of these 13 recipients were transfused more than 5 years ago.

For further information on vCJD and the risk from blood transfusion please click here.
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