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A research letter in this weeks issue of The Lancet details the second case of variant Creutzfeldt-Jakob disease (vCJD) infection that was probably caused by blood transfusion. The rogue prion responsible for vCJD was identified at postmortem five years after an elderly person received a blood transfusion from a donor who later developed vCJD.
The first case of vCJD associated with blood transfusion was announced at the end of last year (see TheLancet 2004; 363: 41721). Also identified at that time were 17 people who had received blood donated from donors who later went on to develop vCJD. The case reported todaywho did not have clinical symptoms of vCJD and died of other causeswas one of those 17 individuals.
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. James Ironside, one of the investigators from the CJD Surveillance Unit, Edinburgh, UK, 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.
Professor Ironside adds: 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.
An accompanying commentary (p. 477) by Kumanan Wilson (Toronto General Hospital) and Maura Rickets (Health Canada) is 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 (removal of white blood cells) for blood transfusion to reduce the risk of possible vCJD transmission was introduced in the UK in 1999.
Authors of a second research letter (p. 529) highlight how leucoreduction only reduced infectivity by around 40 percent in an animal model where hamsters were infected with scrapie-infected tissue. Lead investigator Luisa Gregori (VA Maryland Health Care System/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 article in this weeks issue (p. 521), Jean Philippe Deslys and colleagues (CEA/DSV/DRM/GIDTIP, France) 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.
Source: The Lancet