Creutzfeldt-Jakob Disease (CJD) is a rapidly progressive dementia associated with an incompletely characterized transmissible agent known as a prion. Although the infection in routine processing appears to be extremely low, cases of suspected and/or confirmed CJD requires special handling due to the fact that the prion agent is resistant to most standard disinfection procedures.
What is a Prion?
The normal protein (PrPc) that is active in the brain and other neural tissue is changed to an abnormal protein (PrPsc) by conformational change. The abnormal protein induces replication by contact, which leads each PrPc to adapt to the shape of the shape of PrPsc protein. These PrPsc proteins are known as beta pleats, or plaques called amyloid. Rapid conversion continues across the brain, spreading amyloid deposit, causing damage to the brain and nervous system.
Prion diseases are known as Transmissible Spongiform Encephalopathies (TSE’s), which are a group of rare degenerative brain disorders characterized by tiny holes that give the brain a “spongy” appearance. They are also very stable and almost impossible to destroy. CJD is the most commonly encountered of human prion diseases.
Categories of Human TSE
Of the 6 major categories of human TSE, 4 of them are most familiar:
- Sporadic – accounts for 85-95% of cases and is most common
- Familial – accounts for 5-15% of cases, and is only inherited and not spread by person-person contact
- Iotragenic – accounts for less than 5% of cases, and is spread through accidental transmission via contaminated medical equipment or treatment
- Variant – linked to Bovine Spongiform Encephalopathy (BSE), also known as Mad Cow Disease, and is only transmitted through ingestion of brain material
Level of Transmission
Prion diseases are transmissible and NOT contagious. This means that it is spread only through direct contact with the protein, not through air, physical contact, or exposure. Spouses and other household members have no higher risk of infection than the general population. Patients do not pose a risk to healthcare workers, relatives, or people in the community. Therefore, no one should be denied any medical treatment.
There are 3 levels of infectivity of tissues and body fluids:
- Lymph nodes
No detection of prion disease has been found in all other tissues and body fluids and are considered to be non-infective samples.
There is no cure or treatment for a prion disease. CJD cannot be diagnosed on clinical criteria alone; neurological confirmation through brain biopsy or whole brain examination at autopsy is required for a definitive diagnosis to be made. Hoshimoto’s Encephalitis, intravascular lymphoma, and toxic and metabolic encephalopathies are treatable disorders that mimic CJD. Alzheimer’s Disease, Frontotemporal Dementia and Lewy Body Dementia are untreatable disorders that mimic CJD. All of these must be ruled out before a diagnosis of CJD can be definitively confirmed.
Handling and Precautions
No confirmed cases of human TSE occurring through clear-cut transmission of occupational accident or injury have been documented in healthcare workers. With that, there is no need to be afraid of CJD, just the need to be cautious. Infectious tissues should be properly labeled as to their source and potential of infectivity, and properly processed and stored to avoid cross contamination.
Proper personal protective equipment (PPE) for routine grossing and histology include disposable gown or lab jacket, gloves, safety goggles, face shield, or other protective devices when protecting the eyes and face from slashes and particles is necessary.
Formalin and glutaraldehyde fixed TSE tissue retains infectivity levels for long periods of time, if not indefinitely. As a result, these specimens should be handled with the same precautions as fresh tissue and considered infectious throughout the entire process of fixation, embedding, sectioning, staining, and coverslipping until, or unless, treated with formic acid.
Grossing High Infectivity Specimens
- Examine and cut tissue on a surface covered with absorbent pads that contain impermeable backing. Label cassettes with CJD precautions.
- Treat tissue in cassettes in a chemical fume hood or in front of back draft ventilation with 50-100mL of at least 96% formic acid in a chemical resistant container for 60 minutes using continuous, gentle agitation. (formic acid reduces infectivity to negligible levels by denaturing the proteins)
- Transfer cassettes to fresh 10% NBF for at least 48 hours.
Note that some silver stains for plaques and tangles of Alzheimer's Disease are compromised and additional, untreated tissue should be reserved for subsequent silver staining.
Routine Histology for High Infectivity Specimens
To prevent contamination of equipment and cross-contamination of specimens, all steps should be performed by hand using disposable utensils when possible, unless there is a designated processor and stainer in your lab that is used strictly for CJD specimens. I strongly recommend this even if the tissue has been treated with formic acid...there is no way to clean/decontaminate a piece of equipment once you have exposed it to prions.
- Process by hand in disposable plastic containers on top of absorbent pads
- Perform in a chemical fume hood or in front of back draft ventilation
- Agitate gently during each step
- Collect all solid and liquid waste and store properly until decontamination step
Cassettes may be placed in 70% or 95% reagent alcohol overnight, and processing can be completed the next day.
- Do not place cassettes in holding chamber of embedding center
- Embed cassettes directly from the paraffin used during processing
- Cover surfaces of embedding center, including cold plate, with aluminum foil
- Embed as normal using disposable utensils
- If disposable utensils are not available, place the utensils in water until next use or decontamination step
- Contain all paraffin from processing and embedding, allow to harden, place in a biohazard bag and store properly until decontamination step
Since harsh chemicals should not be used on microtome surfaces, there is no practical way to disinfect a microtome. The following are helpful tips to be taken into consideration...
- Cover appropriate surfaces with aluminum foil, excluding blade holder and blade
- Cover block holder and handle with parafilm
- Cover surrounding countertops with disposable pads lined with plastic to prevent paraffin trimmings from touching surfaces
- A straightened paper clip may be used as a teasing needle, or whatever clever disposable mechanism you come up with
- If disposable forceps are not used, placed forceps in water until next use or decontamination step
- Collect all waste, including paraffin trimmings, and store properly until decontamination step
Cut extra slide labeled with CJD precautions and set aside for additional stains
- Stain by hand in plastic disposable containers on top of absorbent pads
- Perform in a chemical fume hood or in front of back draft ventilation
- Do not use running water
- Coverslip by hand
- Collect all solid and liquid waste, including water, and store properly until decontamination step
All slides, treated and untreated with formic acid, may be handled without specific precautions once the coverslip is sealed and the slide is properly disinfected
TSE agents may persist on work surfaces for an infinite amount of time. They are usually resistant to disinfection and sterilization by most of the common physical and chemical methods for decontamination of infectious pathogens. The safest and most unambiguous method for ensuring that there is no risk of residual infectivity on contaminated instruments and other materials is to discard by incineration. Infectivity is strongly stabilized by air drying or fixation with alcohol, formalin, or glutaraldehyde; therefore, 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 or water.
All contaminated PPE materials should be collected and treated as biohazard waste and disposed of by incineration, or according to your institution.
These materials include:
- Disposable gowns or lab jackets
- Absorbent pads and paper towels
- Aluminum foil
- Safety goggles or other eye protection
- Disposable utensils
- Disposable containers
Immerse instruments and containers in fresh 5% sodium hypochlorite (undiluted bleach) or 2N sodium hydroxide solution for 1 hour. Rinse thoroughly with water, and clean/disinfect as normal.
Flood work surfaces with fresh 5% sodium hypochlorite (undiluted bleach) or 2N sodium hydroxide solution for 1 hour. Rinse thoroughly with water, and clean/disinfect as normal. Surfaces that cannot be treated in this manner can be wiped down with a slightly diluted bleach solution, then repeatedly with water.
Formic acid and formalin may be combined in the same waste container, properly labeled as hazardous waste, and disposed of according to your institution. Infectivity of this solution is negligible due to the formic acid.
Alcohol and xylene may be combined in the same waste container, properly labeled and discarded in the same manner as hazardous waste according to your institution.
Staining solutions, including the water, may be combined in the same waste container and discarded in the same manner as chemical waste according to your institution.
Prions are very deadly and can be intimidating if you allow them to be. By simply coming into contact with a person who has a TSE or even the prion itself, you are not in danger of contracting the disease. It has to be ingested or injected...don’t be scared, be cautious!
- “Chapter 175 Prions and Prion Diseases of the Central Nervous System (Transmissible Neurodegenerative Diseases).” Principles and Practices of Infectious Diseases , Sixth ed., vol. 2, Elsevier, Inc, Philadelphia, PA, 2005, pp. 2222–2228.
- "National Institutes of Health (NIH)." National Institutes of Health. U.S. Department of Health and Human Services, n.d. Web. 28 Oct. 2016.
- "WHO." World Health Organization. World Health Organization, n.d. Web. 28 Oct. 2016.
Written by Shameika Winfrey, HT(ASCP)cm, PBT