A Breakthrough for Chronic Wasting Disease?

A new paper published in the journal PLoS ONE

finds household bleach can deactivate Chronic Wasting Disease prions.

But what does that really mean?

Last week, I traveled to Colorado to go fly fishing and photograph wildlife. I covered a lot of ground, from South Fork to Estes Park. Along the way, dozens of mule deer, whitetails and elk posed for my camera. Each time I clicked the shutter, I wondered, “Does this animal have chronic wasting disease”?

Colorado was the first place this highly contagious, always fatal disease was first discovered in the United States in the 1960’s. As of last July, Colorado Parks and Wildlife reported CWD in 31 of its 54 deer herds, 16 of its 43 elk herds and 2 of its 9 moose herds. Colorado is now just one of 26 states with CWD.

CWD is a transmittable spongiform encephalopathy (TSE), an abnormally folded protein that’s more commonly called a prion.

It’s similar to what causes mad cow disease in cattle and scrapie in sheep. The national Center for Disease Control (CDC) warns us to avoid exposure to it. So far, there are no confirmed cases of CWD in humans, but mad cow disease has jumped the species barrier in the form of Creutzfeldt-Jakob disease, caused by eating contaminated beef products. Hence the warning.

Unfortunately, once CWD comes to an area, it’s impossible to get rid of it. Sick animals shed prions into the environment primarily through saliva, urine and feces. Those prions exist for years on plants and in the soil, where other animals pick them up. There has been no way to stop the spread. But a new paper may offer a starting point.

The News

A new paper in the journal PLoS ONE, “Inactivation of chronic wasting disease prions using sodium hypochlorite”, by Katie Williams, Andrew Hughson, Bruce Chesebro and Brent Race, may offer a bit of hope as researchers try to stop the disease.

Sodium hypochlorite is basically household bleach. The title offers a bit of hope in what is a depressing wildlife situation. Could household bleach be a cure? Well, not quite.

I had spoken to one of the authors of the paper, Brent Race, a staff scientist at the Laboratory of Persistent Viral Diseases at the National Institute of Allergy and Infectious Diseases (NIAID) for my previous Cool Green Science blog on CWD in February. I immediately called him again.

“Does bleach kill CWD?” I asked Race excitedly.

“Technically, you can’t kill CWD because prions aren’t alive, but it does inactivate them in certain situations,” replied Race. “We’ve known for decades that bleach is effective on other prions, like the type that causes mad cow disease. We needed a way to decontaminate our equipment. We thought bleach would work on CWD, too, but it wasn’t tested.”

The Experiment

To see if their hunch proved true, the research team followed a three-step process. Step 1 looked at the effect of bleach on a slurry of brain matter infected with CWD.

“We started with this step to quantitate how many prions bleach would eliminate,” said Race. “It significantly decreased prion seeding… Seeding activity correlates to infectivity. Abnormal prions self-replicate through a biochemical interaction with normal prion-proteins.”

Step 2 determined whether bleach would inactivate CWD prions on nonporous surfaces, like stainless steel countertops and knives. The team dropped strips of large-gauge surgical suture wire into test wells with different concentrations of bleach and water. It worked. However, it took a high concentration of bleach (40 percent) and the metal needed to be submerged for five minutes.

“We were hopeful that a lower concentration of bleach would work, and in less time,” said Race. “That’s a lot of bleach, but it matches historical papers on the use of bleach to deactivate prions.”

Step 3 looked at the effects of bleach on solid pieces of infected tissue. Unfortunately, it had no effect, which was no surprise.

“Bleach doesn’t penetrate tissue well. Most chemicals don’t, except formaldehyde,” explained Race. “We knew that going into the experiment… Bleach is only good as a surface disinfectant. It won’t ever be useful to inactivate CWD in the environment. It gets quenched by soils and other organic matter. It’s only a method for decontaminating equipment.”

As such, the research is primarily of value to field biologists and agency staff dealing with lots of animals. Still, such research can be vital as conservationists rush to understand this rapidly spreading disease.

Using Bleach at Home

Outside of a lab, the most practical application of the team’s findings is cleaning knives, meat processing equipment or other metal objects that come in contact with CWD infected meat. If you do, Race offers these four tips:

1. Don’t overdo it: Use a 50-50 solution of water to bleach because it’s easy to measure. More bleach is not better.
2. Keep an eye on it: If you notice a color-shift or any other change in the object, remove it from the bleach solution. Bleach can be highly corrosive to certain metals.
3. Watch the time: Don’t throw your heirloom knife into the bleach solution and come back in two hours. The prions inactivate in five minutes. Much longer, and the bleach might damage the item.
4. Ventilate the area: Bleach fumes can burn your lungs or cause other respiratory problems in enclosed areas.

Race also warns that all visible chunks of tissue must be removed before depositing an item in the bleach-water mixture, as the bleach won’t penetrate the tissue.

What if you don’t get it all of the tissue off the item you’re trying to decontaminate? Getting most of it is better than nothing.

“A prion can only multiply when it encounters another prion. They need the building blocks, tissue,” explained Race. “They aren’t dangerous on a knife, but that knife can transfer them to a piece of meat where they could amplify. The same is true in the environment. They won’t increase on their own. They need to be inside a susceptible animal, sniffed up a deer’s nose or eaten with a piece of grass.”

The Implications

Bleach isn’t the cure-all for CWD. It only works on nonporous surfaces, but it’s the first thing scientists have discovered that inactivates the abnormal prion that’s wreaking havoc on cervid herds. What’s more, we know the concentration and exposure time for bleach to be effective. And it works any time, today or in three weeks, because, unfortunately, the prions don’t disappear.

“We did the study to provide the science,” says Race, “We’re not making an official recommendation, but we’re hoping that the CDC will comment officially as a result. Now at least I can say ‘this does work’.”