Clinical research YEAR OF ONSET OFvCJD SYMPTOMS
30 25 20 15 10 5 0
UK Non-UK Table 1
background, homozygosity at codon ı29 of the human prion protein gene. There is no evidence, as yet, that other potential risk factors such as occupation and exposure to surgical or dental instruments increase the risk for vCJD. The UK population was exten-
sively exposed to the BSE agent in the human food chain, mainly in the ı980s, and there were fears of a large epidemic of vCJD. However, deaths in the outbreak peaked in 2000 and has subsequently declined with only small numbers of new cases in recent years (Table ı). There have been limited outbreaks of BSE in cattle populations in other countries, mainly in Europe, and potentially infected cattle and cattle products were exported from the UK. As a result, small numbers of vCJD cases have been identified in other countries (table 2) and this includes cases that were likely exposed to BSE while living in the UK. Just as with the British outbreak,
there has been a decline in the number of new cases of vCJD in countries outside the UK in recent years. It is possible that the primary outbreak of vCJD may be nearly over, but there is the possibility of further cases in individuals with alternative genetic backgrounds and extended incubation periods. vCJD differs from other human
prion disease as the infectious agent is found not only in the central nervous system, but also extensively in lymphoreticular tissue such as the spleen and lymph nodes. This
has resulted in concern about trans- mission of infection through blood transfusion or surgical instruments that contact these infected periph- eral tissues. There is evidence of trans-
mission of vCJD from person to person through blood transfusion, including three individuals who developed vCJD six to eight years after receiving blood donated by individuals who themselves developed vCJDı3. Concern about secondary transmission of vCJD has been heightened by evidence from prevalence studies of routine appendicetomy specimens, which suggest that there may be thousands of individuals in the UK who are cryptically infectedı4. These individuals may never
develop clinical disease, but may have asymptomatic infection in lymphoreticular tissues, which might be present for many years. While secondary transmission of vCJD has been identified via blood transfusion, there is no indication of transmission by other routes. However, the incubation periods
in human prion disease can extend to decades and the period of obser- vation is currently too short to exclude the possibility that further routes of transmission of vCJD will be identified. This suggests that measures to minimise human exposure to infection continue to be important. One area of concern for transmission of vCJD is through dental procedures as discussed below.
Prions and dentistry The Department of Health has published two risk assessments assessing the potential for vCJD transmission risks via dentistry. The first was published in 2003 and the second in 2007. Both attempted to clarify the level of risk to public health and the relative impact of risk reductions methods. This was dealt with on a number
of levels: the possible scale of risk, infectivity in relevant tissues, efficacy of decontamination and the epidemiology of vCJD. Each of these inputs is compounded by multiple uncertainties and the very large number of dental procedures undertaken annually means that even small transmission risks per procedure could create an appreci- able risk to public health. The report further describes that
the impact of dentistry on vCJD transmission dynamics could range from no detectable effect to several hundred transmissions per annum, dependent on a number of variables including infectivity in oral tissues and efficacy of instrument decon- tamination. The Scottish approach to limiting
the risk of iatrogenic CJD via opera- tive dental procedures followed on from work undertaken first by the ‘Old’ group, reported in 200ı, which included an observational survey of Sterile Service Departments, general medical practices and five general dental practices in Scotlandı5. This
Continued » Scottish Dental magazine 57
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