The likelihood of a large number of future cases of vCJD remains small claim researchers from Imperial College London.
According to research published today in Journal of the Royal Society Interface, the team believe there will be around 70 future cases of vCJD arising from the consumption of BSE-infected beef. At most this could rise to a total of around 600 deaths, although the researchers feel this is unlikely.
This work follows on from a study in 2003 at Derriford Hospital, Plymouth, which looked at tissue from appendectomies. The researchers found a higher prevalence of vCJD than expected from clinical data alone, indicating that around 3,800 individuals in the UK could test positive.
The team at Derriford found three positive samples among 12,764 tonsil and appendix samples and from this concluded that around 3,800 individuals could be at risk across the UK. Despite this, only one of the three samples positively matched tissues taken from those with clinical disease. The interpretation of the other two samples was less certain, and could indicate individuals infected with vCJD that do not go on to develop clinical symptoms – so called sub-clinical infections.
Dr Azra Ghani, from Imperial College London, and based at St Mary's Hospital, comments: "Since 2000 there has been a decline in the number of clinical cases reported. One reason for the discrepancy between the high estimated number of positive tests and low number of actual recorded clinical cases could be that many infected individuals do not go on to develop clinical disease in their lifetime."
Using computer modelling the team ran a number of different scenarios. The first scenario in which 90 per cent of infections are sub-clinical suggested that relatively few future cases would arise through primary transmission, such as eating BSE infected beef. The other 'worst case' scenario, where all genetic groups were susceptible, suggested that a five fold rise could be possible, although this was felt to be unlikely, due to the low number of clinical cases currently recorded in these other genetic groups.
Dr Ghani adds: "Although our results indicate there is little chance of large numbers of vCJD infections from primary transmission, we have not taken into account the possibility of additional cases infected by blood transfusion. This could result in more clinical cases emerging at a later date."