How deadly prions are destroyed

Mad cow disease, chronic wasting disease and similar ailments are all thought to be caused by misshapen forms of special proteins known as prions. In the case of chronic wasting, research shows infection can occur even by proximity to sick deer.

So how do you safely dispose of stricken animals?

It isn't as simple as burying their carcasses, or even incinerating them.

Prions are simply proteins, not living organisms, and they can survive almost anything, even hundreds of degrees of heat. Placing infected tissue in a landfill simply removes it, but scientists worry that the prions can leach through soil and groundwater, and spread.

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Incineration is possible, but it isn't as easy as burning the carcass in a fire. Temperatures of more than 1,100 degrees Fahrenheit — sometimes up to 1,800 degrees — are required to effectively neutralize prions. Unlike most bacteria, regular cooking won't help at all.

"Disposal issues are tough," says Barbara Powers, director of Colorado State University's Veterinary Diagnostic Laboratory.

Even many of sterilization techniques used in hospitals, such as autoclaving, are not necessarily effective — though some may be when infected material is dipped in sodium hydroxide, or lye and heated well above the boiling point of water.

A combination of heat — about 275 degrees Fahrenheit — and bursts of unimaginably high pressure — over 100,000 psi — showed promise in reducing prion infectivity, at least in processed meats like hot dogs, in research published last year.

And a similar method has become the default process for getting rid of infected animals. Large vat-like machines known as alkaline hydrolysis tissue digesters, one of which Powers' lab operates, can essentially dissolve entire carcasses.

Infected material is placed in a solution of potassium hydroxide — also known as caustic potash — for at least six hours, at 300 degrees Fahrenheit and 60 psi, about four times ambient air pressure.

All remains at the end is a sterile brown, syrupy liquid that can be hauled away to compost.

"It's like a big steam cooker," Powers says. "That'll take care of the prions."