1,303 positive cases of BSE have been confirmed in ROI so far. Based on these figures, the total number of BSE-infected animals in ROI has been estimated at 22,000. This compares with an estimated 827,500 cases in the UK.
To date there have been 137 confirmed cases of vCJD in the UK, and only one in ROI. As it is not possible to construct estimates of future epidemics from this case alone, the researchers, from Beaumont Hospital, Dublin and Imperial College, London, calculated the exposure of the Irish population to BSE infected beef, relative to the exposure of people in the UK. This enabled them to use the comprehensive data on BSE and vCJD in the UK, where the epidemic has peaked, to calculate the future risk to the people of Ireland.
2.5% of the ROI population were exposed to the same risk of eating BSE-infected beef as other UK residents, as they were living in the UK during the 'at-risk' period (1980-1996).
Those who stayed at home were exposed to BSE via BSE-infected domestic beef products or products imported to Ireland from the UK. The researchers used information from UK Customs & Excise and the Department for Environment, Food and Rural Affairs (DEFRA) to calculate that the Irish consumed 0.26% of the beef products produced in the UK (c. 2,148 BSE infected cattle). They also discovered that only 10% of the annual Irish Beef Industry output was consumed in Ireland (c. 2,200 infected cattle).
By plugging these figures into a statistical model based on the annual number of cases of vCJD seen in the UK and the relative population sizes of the UK and ROI, the scientists calculated that there was likely to be only one further case of vCJD in Ireland, with an upper limit of 15 cases.
Their estimate only considers those people who will catch vCJD from infected beef or beef products. It does not include any cases arising through secondary transmission, for example via surgical equipment that had previously been used on an infected patient.
The researchers believe that, "the development of a suitable blood test that would allow screening of large numbers of the population would prove extremely valuable in further quantifying the risk to the Irish population of vCJD". This would help to identify the number of people who were suffering from vCJD, but had not yet shown symptoms. Performing surgery on these people, could potentially lead to contamination of surgical instruments, and cause further spread of the disease.
Nor does the estimate take into consideration the possibility that meat other than beef could have been infected with BSE. The researchers write, "To ensure that we are identifying all vCJD cases, and also to ensure that the disease is not entering the human population by a more surreptitious route (e.g. via different animals) it is of considerable importance that the Irish CJD Surveillance Unit continue to be notified of all possible cases of transmissible spongiform encephalopathies."
This article is freely available online, according to BioMed Central's policy of open access to research articles:
vCJD risk in the Republic of Ireland
Michael S Harney, Azra C Ghani, CA Donnelly, Rory McConn Walsh, Michael Walsh, Rachel Howley, Francesca Brett, Michael Farell
BMC Infectious Diseases 2003, 3:28
Published 26th November 2003
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