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ABC of Safety in the Biological Sciences
CREUTZFELDT-JAKOB DISEASE
Creutzfeldt-Jakob disease is a progressive, fatal condition of the central nervous system caused by a prion. The causative agent - a prion - is an aggregate of protein rods that contain either DNA or RNA. Both sexes are affected and the disease commonly occurs in middle life. Dementia appears after a period of vague prodromal symptoms and rapidly progresses to coma and death, usually within two years of onset, although survival for longer periods has been reported.46 Dementia is often accompanied by other neurological disturbances.
Twenty Four cases of transmission of the agent in health care workers (four in medical laboratory personnel) have been documented.47-52 Therefore it is necessary to institute the most stringent safety measures in laboratories and autopsy rooms where the possibility of encountering this agent exists.53
Prions represent the most chemically resistant and untreatable of all infectious diseases. Most known disinfectants are ineffective, these include boiling water, formalin, alcohol, phenol, glutaraldehyde, hydrogen peroxide, ionising or UV radiation,54 or dry heat to 360°C. Enzymes are also ineffective. The methods which are thought to be effective include the following:
- sterilisation by autoclaving for 4.5 hours at 15 psi and a temperature of 134°C
- autoclaving in 1 mol/l sodium hydroxide for 1.5 hours is also effective54
- immersion of formalin fixed material in 96% formic acid for 60 minutes
- washing working surfaces with 2N sodium hydroxide for 60 minutes (except aluminium surfaces)
- immersion in sodium hypochlorite (20,000 ppm available chlorine)for 60 minutes and incineration.55 It must be stressed that formalin appears to preserve infectivity of prions during autoclaving so that post-formalin autoclaving is not an effective form of decontamination. The safest way of ensuring destruction of the agent after fixation is in a high temperature incinerator.
Great caution must be exercised to avoid accidental percutaneous inoculation of infected material.56 If accidental puncture does occur the affected area should be treated with one of the recommended skin disinfectants immediately although this may be ineffective. Recommended procedures include iodine or phenol-containing preparations, 0.5 Mol/l sodium hydroxide or 1:3000 potassium permanganate.57
Autopsy and surgical pathology
procedures
Because of the nature of the agent necropsy
and histological technique must be designed to contain the infected
tissue and decontaminate any exposed surfaces.55 Only
those persons directly involved in the autopsy should be present and
should wear long sleeved gowns, gloves and a mask. The skull and
spinal canal should be opened as usual with an oscillating saw,
without cutting the brain or spinal cord. All tissues must be
regarded as infectious although evidence now suggests that the
infective agent is most concentrated in nervous tissue,
cerebrospinal fluid and lymphoid tissues.55 The sink in
which water from the autopsy table collects should be plugged and
all wash water collected. This should be autoclaved or treated with
greater than 4 volumes of 5% hypochlorite and left for a minimum of
two hours before discarding. Instruments, gloves, drapes, saw blades
and any other materials used in the autopsy should be autoclaved as
previously described, wherever possible use disposable instruments.
Surfaces should be cleaned with an appropriate disinfectant (2mol/l
sodium hydroxide), followed by scrubbing with strong detergent in
hot water followed by further disinfection. Special attention should
be paid to the external disinfection of containers used for the
collection of tissues.
In the laboratory a dedicated room or limited section of the laboratory should be used enabling thorough decontamination. Wherever possible disposable items which can be incinerated should be used. All tissues must be considered as fully infectious even after prolonged fixation in formalin and histological processing. All liquids used in processing including alcohols and clearing agents, should be pooled and decontaminated before disposal. Glassware, forceps and tissue carriers can be decontaminated in 5% hypochlorite (note this is an oxidising agent and a corrosive and will attack some metals at this concentration). The microtome blade used to cut the tissue must also be decontaminated with special care taken to avoid cuts. Waste wax from rough cutting can be collected and decontaminated by incineration. The microtome should be well cleaned with 0.5% sodium hypochlorite (at this concentration the solution is not corrosive). The section can be decontaminated with dilute potassium permanganate before staining and blocks should be stored in a sealed air tight container with a visible warning that the contents are infectious.
Tissue from cases of Creutzfeldt-Jakob disease should not be accepted for teaching of gross anatomy and any specimens in pathological teaching collections should carry a warning and be handled with caution.
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