Stopping Zombie Deer Disease in its Tracks
Bleach as a Decontaminant for Chronic Wasting Disease Prions
Background
If you are a hunter, conservationist, or both, you likely already know about Chronic Wasting Disease (CWD). Even if you are neither, CWD is an important public health concern. This disease, caused by a malignant misfolded protein called a prion, has spread across parts of the continental United States and can be found in 25 states, including Pennsylvania. Its primary victims are deer species (cervids) such as white-tailed deer, mule deer, elk, and moose. It has an incubation period anywhere from twelve months to over two years, and its symptoms are straight from a zombie movie. Infected animals show neurologic signs such as altered gait, head tremors, excessive salivation, and difficulty swallowing. Victims, often with visibly necrotic flesh, become emaciated and die within a few months of showing symptoms.
Like most other prion diseases, CWD is infectious and can be transmitted between cervids. Healthy prion protein (PrPC) is a normal part of cells, but in diseases like CWD, these proteins become misfolded into malignant PrPSc and resist degradation. PrPSc tends to aggregate especially in the brain and spinal cord and cause abundant PrPC to misfold into the diseased form. Because of its ability to proliferate, PrPSc acts as an infectious agent which spreads the disease to new hosts. There have been no confirmed cases of CWD transmitted to humans, but Bovine Spongiform Encephalopathy (Mad Cow disease), another prion disease, has made the jump to humans. Since the potential for zoonotic transmission exists, limiting contact with CWD is very important.
To test for prion diseases, real-time quaking-induced conversion (RT-QuIC) can be used. This method of testing exploits the ability of PrPSc to cause PrPC to misfold. The assay involves introducing a small amount of sample suspected to have PrPSc present and incubating it with a solution of PrPC over about 48 hours. The sample is continually scanned for protein activity, and if PrPSc aggregates to a detectable level, then the sample is inferred to be positive for the misfolded form of the protein.
Misfolded prion proteins are notoriously hard to destroy and can resist extreme temperatures and many chemical solvents. However, bleach is a promising decontaminant that can eliminate prion proteins and happens to be readily available to the public.
Summary: Bring Your Own Bleach
In the study, samples of CWD-positive deer brains were mixed with varying solutions of bleach (6% sodium hypochlorite) to observe activity after mixing. In the first part of the experiment, brain homogenate was combined with varying bleach concentrations ranging from 1% to 40% mixed with water. Some samples were incubated for one minute, while others were incubated for five minutes. The samples were then diluted and tested via RT-QuIC to observe activity. Only the lowest bleach concentration (1%) incubated for one minute did not eliminate PrPSc activity. All other samples (10–40% bleach and 1 or 5 min) eliminated all seeding or proliferating ability of the misfolded prion protein.
To simulate cleaning of cutting tools like knives and saws, bleach was also tested for its ability to decontaminate steel wires coated with CWD-positive deer brain homogenate. Since typical field dressing of animals does not involve contact with brain or spinal tissue where PrPSc concentrations are the highest, the bleach concentration needed to disinfect the wires is likely overkill for contact with muscle, skin, and blood. This experiment showed a much higher threshold for decontamination: 40% bleach for 5 minutes was the only assay that eliminated all PrPSc from the steel wires.
Solid pieces of brain matter only a few millimeters across were also soaked in bleach to test for decontamination, but the bleach did not penetrate enough to eliminate activity in any samples tested. This proves the need for thorough scrubbing of tools to remove any visible pieces of tissue. Overall, this study proves bleach effective in inactivating malignant prion proteins, and rising CWD in U.S. deer populations will likely make bleaching tools a necessity for hunters and biologists who want to reduce their contact with this disease.
Further Reading:
CDC Information on Prion Diseases
RT-QuIC Test for Prion Diseases
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