Although Creutzfeldt-Jakob disease (CJD) is very rare, the condition can be difficult to prevent.
This is because most cases occur spontaneously for an unknown reason (sporadic CJD) and some are caused by an inherited genetic fault (familial CJD).
Sterilisation methods used to help prevent bacteria and viruses spreading also aren't completely effective against the infectious protein (prion) that causes CJD.
But tightened guidelines on the reuse of surgical equipment mean that cases of CJD spread through medical treatment (iatrogenic CJD) are now very rare.
There are also measures in place to prevent variant CJD spreading through the food chain and the supply of blood used for blood transfusions.
Since the link between bovine spongiform encephalopathy (BSE, or "mad cow" disease) and variant CJD was confirmed, strict controls have been in place to stop BSE entering the human food chain.
These controls include:
In the UK, there have been 4 cases where variant CJD has been transmitted by blood transfusion.
In each case, the person received a blood transfusion from a donor who later developed variant CJD.
Three of the 4 recipients went on to develop variant CJD, while the fourth recipient died before developing variant CJD but was found to be infected following a post-mortem examination.
It's not certain whether the blood transfusion was the cause of the infection, as those involved could have contracted variant CJD through dietary sources.
Nevertheless, steps were taken to minimise the risk of the blood supply becoming contaminated.
These steps include: