Prions & vCJD

Prions are “infectious protein particles” that, unlike other infectious microbes, contain no genes (DNA) only protein.

Prions Disease

Prions cause a group of rare, debilitating and always fatal degenerative brain diseases called Transmissible Spongiform Encephalopathies (TSEs).

TSEs have a long asymptomatic incubation period lasting 10-40 years. The commonest TSE is the sporadic form of Creutzfeldt-Jakob disease (CJD).

There are 80-90 new cases per year in the UK. 

The Link Between vCJD and Mad Cow Disease

The most notorious of the TSEs is vCJD or “BSE- Mad Cow Disease” caused by farmers feeding sheep infected with the prion disease Scrapie to cattle.

vCJD differs clinically from sporadic CJD in that it affects younger people (median age of death of 28), has a shorter incubation period, with prominent early psychiatric symptoms.

In the UK, vCJD was first diagnosed in humans in 1996, and was linked to the consumption of meat products infected with Bovine Spongiform Encephalopathy (BSE).

The millennium saw the highest number of diagnosed cases but since then the number of new clinical cases has been gradually declining.  As the epidemic of BSE in cattle has been controlled, scientists suggested that any successive waves of infection are likely to arise not from eating infected beef but from person-to-person spread via inadequately decontaminated medical and dental instruments.

In 2013 the total number of cases of vCJD reported in the UK was 174 all of whom are now deceased. But vCJD is not likely to disappear for a number of years as one in 2000 of the UK population are estimated to be infectious carriers of vCJD.

Most carriers will probably not develop clinical disease.

Distribution of Prions in the Body

CJD and vCJD infectious prion proteins comprise of an abnormal pathogenic form of a normal human cell surface protein known as PrP.

They enter the body through inoculation or direct contact with oral tissues and the gut.

Prions are not uniformly distributed in the body of infected individuals. Brain and central nervous tissue (including the retina) pose the highest risk, lymphoid tissues such as the tonsils, cornea and dura mater are medium risk and most other body fluids and tissues have a low or negligible risk.

Routes of Spread of Prions and Endodontic Instruments

Normal social or routine clinical contact with a prion disease carrier does not represent a risk to the dental team.  However, hospital acquired cases of CJD have been associated with the administration of hormones prepared from human pituitary glands, dura mater grafts, corneal graft and  inadequately decontaminated neurosurgical instruments.

Four cases arose from blood transfusions and 1 case from plasma products donated by people who appeared healthy at the time of donation, but later died of vCJD. 

Prions were isolated from the trigeminal ganglion and tonsils from vCJD patients at post mortem and in animals infected with vCJD from the dental pulp and gingivae.

For this reason the HTM 01-05 restricts endodontic files and reamers to single use only, thereby eliminating these instruments as a route of transmission of vCJD. Endodontic instruments that are designated as SINGLE USE ONLY must not be reused, even on the same patient.

Endodontic equipment designated by the manufacturer as reusable can be decontaminated.  However, they can only be used on the same patient for the duration of a single course of treatment, for example multi-visit root canal treatment, and then must be disposed of as hazardous infectious sharps waste.

Management of Carriers of vCJD/CJD

Over 6,000 potentially infected carriers have been notified that they pose an increased public health risk to other people.

Such people can be treated in the same way as any member of the general public, for example their used dental instruments are decontaminated according to the essential quality requirements of HTM 01-05.

If the patient requires a referral for oral or maxillofacial surgery, then the surgeon should be informed of the patient’s status in the referral letter.

Instruments used during their surgery are quarantined until a definite diagnosis of vCJD or CJD is made, and then if positive, re-used exclusively on the same patient or destroyed by incineration.

It is recommended by the Department of Health that all patients about to undergo any type of surgery should be asked when taking a medical history “Have you ever been notified that you are at increased risk of CJD or vCJD for public health purposes?”

Prions and Decontamination

Prions bind strongly to stainless steel instruments.

Alcohol based disinfectant and chlorhexidine fix prion proteins onto the surface of instruments further preventing their removal and destruction.

Sterilisation is effective in killing and destroying bacteria and viruses, thereby reducing prion infectivity, but cannot reliably destroy and remove vCJD from contaminated instruments.

Therefore, effective cleaning is the most important step in the HTM 01-05 decontamination cycle as it removes prions from the surface of the instrument.