TSEs are known to be transmissible both within and between species via the inoculation of infected tissue or dietary exposure to prions.10 The first evidence for the transmissibility of human prion diseases was from kuru, a disease discovered in the late 1950s in Papua New Guinea. Transmission of kuru was through cannibalism.10 More recent evidence for the transmission of human prion diseases comes from the 267 documented cases of iatrogenic CJD.11 These transmission events occurred owing to accidental exposure to prions through medical procedures or treatments. The most common forms of iatrogenic transmission have involved dura mater grafts and growth hormone treatment, but others have included corneal transplants and neurosurgery.11 Concerns about the transmissibility of vCJD are heightened by the fact that the tissue distribution of PrPres in vCJD has been shown to be more widespread than in other forms of CJD; specifically, the lymphoreticular system is involved in vCJD. Thus surgical procedures posing potential risks for transmission include tonsillectomy, appendicectomy, and lymph node and gastrointestinal biopsy.27 PrPres have been found in the appendix 2 years prior to the onset of symptoms, reinforcing fears of transmission from preclinically affected individuals.15
It is generally considered that invasive surgery poses a higher risk for vCJD transmission because the introduction of prions directly into tissues is generally a more efficient route than oral exposure.30 Furthermore, same-species transmission of TSEs is also generally more efficient than between-species transmission.30
THERE IS NO METHOD PROVEN TO STERILISE AGAINST VCJD WITH CERTAINTY
Prions, the infectious agents in TSEs, are more resistant to conventional sterilisation and decontamination procedures.5 This resistance to classic decontamination methods, combined with knowledge of iatrogenic transmission, poses a serious challenge for public health.9 Published guidelines recommend the employment of single-use, disposable instruments. It is also recommended that potentially contaminated devices be incinerated after they are removed from circulation.31 Prions have been shown to retain infectivity even after incineration or after being subjected to high autoclave temperatures.31
In a case at the Middlesbrough General Hospital, UK, £90 000 worth of surgical instruments had to be withdrawn after the diagnosis of CJD in a patient who had previously undergone a brain biopsy.32 The Department of Health subsequently recommended that all surgical instruments used for brain biopsy of non-focal lesions be quarantined until a definitive diagnosis has been obtained.33 At this time, the only secure way to guard against the transmission of vCJD through invasive surgery involving high risk tissues or organs is to dispose of medical equipment.