The first case of variant Creutzfeldt-Jakob disease (vCJD) associated with blood transfusion was announced at the end of last year. At this time researchers identified 17 people who had received blood donated from donors who later went on to develop vCJD.
Now the rogue prion responsible for vCJD has been identified at postmortem 5 years after an elderly person received a blood transfusion from a donor who later developed vCJD.
The case reported today did not have clinical symptoms of vCJD and died of other causes, however this case was 1 of the 17 individuals identified last year.
The current case is the first of its kind to identify a heterozygous genotype for the prion protein, suggesting that a larger population of people could become infected.
Dr James Ironside, from the CJD Surveillance Unit, Edinburgh, Scotland, comments, “This finding has major implications for future estimations of numbers of vCJD cases in the UK, since individuals with this genotype constitute the largest genetic subgroup in the population".
"This subgroup might have a different incubation period after exposure to either primary infection by the bovine spongiform encephalopathy (BSE) agent or secondary infection by blood transfusion".
"A very lengthy incubation period might explain why no clinical cases of vCJD have yet been observed in this subgroup”.
“This case highlights the need for continuing surveillance for CJD in the UK, and strongly reinforces the role of the autopsy in the investigation and diagnosis of both clinical and preclinical forms of human prion disease”.
In an accompanying commentary in the same publication, Dr Kumanan Wilson from Toronto General Hospital and Dr Maura Rickets from Health Canada are supportive of UK policies introduced to limit the spread of vCJD.
With regard to the blood-transfusion case, Dr Wilson comments, “The true clinical and public-health significance, with respect to the issue of whether the individual would have subsequently developed clinically evident vCJD or whether this individual poses a risk for iatrogenic transmission of the disease, remains uncertain".
"Nevertheless, combined with the animal studies by Houston and Hunter and their colleagues showing transfusion transmission of the disease in preclinical models, and the previous case report of probable transfusion transmission, there now appears to be sufficient evidence that individuals without clinical signs of vCJD harbor, and therefore potentially transmit, the infection”.
A policy of leucoreduction for blood transfusion to reduce the risk of possible vCJD transmission was introduced in the UK in 1999.
The authors of a second research letter in this week's Lancet highlight how leucoreduction only reduced infectivity by around 40% in an animal model.
Dr Luisa Gregori from the VA Maryland Health Care System and University of Maryland, USA comments, “Although leucoreduction is a necessary step for removing white-cell-associated TSE infectivity from blood, this process is insufficient to remove the risk from an infected transfusion unit”.
Transmission of vCJD from surgical instruments is another public-health concern, especially as the prion protein responsible for vCJD is resistant to conventional sterilizing procedures.
In an additional article this week, Dr Jean Philippe Deslys and colleagues identify a new technique for disinfecting prion-contaminated medical devices.
They report how specific alkaline agents or an original vaporized hydrogen peroxide treatment can be effective decontaminants without damaging delicate medical or surgical instruments; conventional autoclaving alone does not fully reduce transmission risk and can often damage surgical devices.
Dr Deslys comments, “Decontamination of prions from surgical instruments has been a major problem since vCJD was first identified".
"The results of our study should provide reassurance that practical solutions now exist which can be implemented without delay to reduce risk of prion transmission from medical and surgical instruments”.