Variant Creutzfeldt-Jakob disease and the risks from blood transfusion
196 people have died from vCJD in the UK since it was first detected in 1996. While the primary route of transmission has been through eating infected meat, concern has recently focussed on onward human to human transmission. In this article Dr Azra Ghani reviews vCJD and the risks from blood transfusion.
- Variant Creutzfeldt Jakob Disease (vCJD) belongs to a family of Transmissible Spongiform Encephalopathies.
- Incidence of vCJD has been declining since 2000.
- Genetic factors influence susceptibility to infection and the incubation period of the disease.
- Uncertainty exists about the number of individuals harboring infection.
- Risk of acquiring vCJD from blood transfusion is linked to the prevalence of infection, the rate at which blood is used, and the ages of the donor and the recipient.
- Leucodepletion reduces infectivity by 40%.
- Individuals who have previously received blood a transfusion are banned from giving blood.
Declaration of interests: This work was supported by the Department of Health. The views expressed in this publication are those of the authors and not necessarily those of the Department of Health.
Whilst the incidence of clinical cases of variant Creutzfeldt-Jakob disease (vCJD) has declined in recent years, concern has increased over the possibility of an epidemic arising through blood transmission. Here we review important aspects of the disease and its epidemiology and consider their implications for the risks from blood transfusion.
vCJD is one of a family of neurodegenerative diseases known as Transmissible Spongiform Encephalopathies (TSEs). The oldest known disease of this type is scrapie, which affects sheep and has been endemic in most parts of the world for over 200 years. Bovine Spongiform Encephalopathy (BSE) or ‘mad cow disease’ also belongs to this family of diseases. Human forms of the disease include CJD, Gerstmann-Straussler-Scheinker disease (GSS), fatal familial insomnia and kuru. The latter was first discovered in the 1950s among the Fore population in Papua New Guinea, with the epidemic resulting in approximately 2,500 deaths from 1957 onwards. The disease was transmitted through cannabilistic consumption of, or contact with, human tissues during funeral rites. Sporadic cases of CJD occur worldwide with an annual incidence of approximately one case per million of the population, whilst inherited forms of the disease are even rarer (approximately 10% of all cases of CJD). Transmissible Spongiform Encephalopathies are characterised by spongiform changes in the brain, neuronal loss and amyloid plaque formation, which occur with the accumulation of an abnormal protease-resistant prion in the brain. A particular characteristic shared by these diseases is a long and variable incubation period, typically of many years, during which there is little or no detectable immune response to the pathogen.
vCJD was first identified in the UK in 1996 and was distinguished from classical CJD by its different clinical presentation and neuropathology.1 Through March 2006 there have been 154 deaths from vCJD in the UK with a further six probable cases remaining alive. Elsewhere cases have been reported in Ireland, France, Italy, United States, Canada, Saudi Arabia, Portugal and Japan.
The incidence of deaths in the UK peaked in 2000 with 28 deaths and has declined thereafter with only 5 deaths in 2005. The median age at death has remained stable at approximately 28 years, with a significant excess of cases in those aged 10 to 40 years. This excess is most likely to be due to increased susceptibility in the young, but could also be due to greater exposure. Host genetics also influence susceptibility, with all clinical cases to date having a genetic characteristic shared by approximately 40% of the population (methionine homozygous at codon 129 of the prion protein gene). Recent findings have shown that other genetic groups are also susceptible to infection2 but to date no clinical cases have been observed.
The primary route of transmission of vCJD from cattle to humans is believed to occur through consumption of BSE-infecte