Large vCJD epidemic unlikely
It is unlikely that a large number of people will die from vCJD, the human form of BSE, according to researchers from Imperial College London.
They predict there will be about 70 future deaths from the disease, although there is a small chance this number will reach 600.
Since the degenerative and fatal brain condition, new-variant Creutzfeldt-Jakob disease, was identified in 1995 and the link to beef contaminated with BSE recognised as the cause, efforts have been made to predict the likely extent of mortality.
Last year, a study of removed appendix and tonsil tissue from 12,700 people found signs of vCJD in three samples, which is the equivalent of 3,800 carriers across the entire UK population.
But a discrepancy exists between this high number of expected positive tests and the actual number of vCJD cases, which has reached only 147 so far with an apparent peak of 28 in 2000.
The tonsil and appendix study, from Derriford hospital, provided a clue to explain this inconsistency. Only one of the three vCJD positive samples matched tissues taken from those with the actual disease.
After further analysis, the Imperial College London team says one possible explanation is that many infected individuals do not go on to develop symptoms of the disease. In this scenario the researchers predict 70 future cases.
Dr Azra Ghani said: “We have seen this happen in animal studies, and it is the explanation that best fits the data.”
Another possible explanation arises from the observation that, until last year, every existing case of vCJD has occurred in people with particular genetic characteristics. There is the possibility that people with a different DNA profile may exhibit a longer incubation period before they show signs of the disease, meaning another peak in vCJD cases may occur.
This “worse case” scenario would bring the likely vCJD death toll to around 600.
It is suspected that last year’s single exception to the genetic trend in vCJD cases was the result of infection following a blood transfusion, and this form of transmission may push the fatality rate up further.
Dr Ghani warns that the research team’s calculations only take into account the chances of vCJD infections from primary transmission, and not the possibility of additional cases infected by blood transfusion.
“This could result in more clinical cases emerging at a later date.”
The study was published in the Journal of the Royal Society.
