Prions are characterized by extreme resistance to conventional inactivation procedures including irradiation, boiling, dry heat, and many chemicals (formalin, beta-Propiolactone, alcohols). Fixation with alcohol, formalin, or glutaraldehyde strongly stabilizes the infectivity of prions and makes them more difficult to inactivate. Formalin-fixed and paraffin-embedded tissues, especially of the brain, remain infectious. Consequently, contaminated materials should not be exposed to fixation reagents and should be kept wet between the time of use and disinfection by immersion in chemical disinfectants. Fixed material that contain or may contain prions must be disposed of as "prion waste". Dispose of PLP contaminated waste via standard biohazardous waste disposal methods. If PLPs are expected or suspected to be resistant to standard decontamination methods, follow prion disinfection methods described below.
Note: Be sure to decontaminate all equipment prior to maintenance or service work.
Effective Methods for Inactivation and Disinfection:
- A sodium hypochlorite solution containing at least 2% available chlorine (20,000 ppm) 2, 3, with a one-hour contact time. Note: 5.25% sodium hypochlorite equal to approximately 50,000 ppm or 5% available chlorine. If using 5.25% household bleach, make a 2:3 v/v dilution (2 parts undiluted household bleach and 3 parts water) in order to make 20,000 ppm available chlorine.
- Freshly made 2 N NaOH with a contact time described below3, 4, 5
- The alkaline hydrolysis process using a strong alkaline solution, heat and pressure performed in the Veterinary Diagnostic Laboratory (VDL) Tissue Digester3
Inactivation Using Physical Methods:
- Autoclaving at 134°C for 18 minutes5 or autoclave at 132°C for 1 hour4
- Incineration3
Procedures for Disinfection of Surfaces and Heat-Sensitive Laboratory Equipment3
- Flood with 2 N NaOH or sodium hypochlorite solution (20,000 ppm available chlorine) and ensure surfaces remain wet for one hour. Mop up and rinse with water.3
Disinfection of Heat-Resistant Reusable Lab Equipment3
- Immerse in 1 N NaOH or sodium hypochlorite (20,000 ppm available chlorine) for 1 hour. Transfer into water and autoclave (gravity displacement) at 121ºC for 1 hour; or
- Immerse in a pan containing 1 N NaOH, heat in a gravity displacement autoclave at 121ºC for 30 minutes. Rinse with water; or
- Immerse in 1 N NaOH or sodium hypochlorite (20,000 ppm available chlorine) for 1 hour. Remove and rinse instruments with water, transfer to open pan and autoclave at 121ºC (gravity displacement) or 134ºC (porous load) for 1 hour. Water used to rinse the instrument must be treated as infectious waste and autoclaved.
Biosafety cabinet (BSC) decontamination
BSCs must be decontaminated with 1 N NaOH or sodium hypochlorite (20,000 ppm available chlorine) for 1 hour and rinsed with water.3
Spill Cleanup
- Notify other lab workers that a spill has occurred and that an evacuation is necessary.
- Post a biohazard spill sign at the lab door.
- Direct other workers not to enter the lab.
- Wear appropriate PPE (see Safe Practices section) prior to spill cleanup.
- Cover spill with paper towels or other absorbent materials.
- Saturate with 2 N NaOH or 2% sodium hypochlorite (20,000 ppm available chlorine) and keep spill area wet for at least 60 minutes. If possible, leave the lab to avoid prolonged breathing of fumes.
- Pick up any sharps, including broken glass, with forceps and place in yellow sharps container.
- Wipe spill area with disinfectant and clean paper towels.
- Dispose of all cleanup materials in yellow waste bag.
- Remove PPE and discard in the yellow waste bag. Wash hands.
- Report all spills to lab supervisor.
References:
[2] USDA Chronic Wasting Disease
[3] CDC/NIH Biosafety in the Microbiological and Biomedical Laboratory, 6th edition, Section VIII-H, Prion Diseases, pp. 360-362
[4] Canada Pathogen Safety Data Sheets: Infectious Substances – Creutzfeldt-Jakob agent, Kuru agent.
[5] WHO Infection Control Guidelines for Transmissible Spongiform Encephalopathies, p. 29