Making Grad Work Easier
In "The Companions of Mad Cows" a couple of years ago we mentioned that veterinarians in Alabama had diagnosed mad-cow disease, bovine spongiform encephalopathy (BSE) in a downer cow. According to the Wall Street Journal article, officials had buried the cow on a farm in Alabama, but refused to divulge where. They were also searching for the bovine's "companions", to assure the disease was confined to one cow and hadn't been contracted through feed eaten by many cows. (Scientists don't think BSE is transmissible from cow to cow.) We wrote in that post: "we suspect that perhaps someday when the BSE stricken cow has long since been forgotten and decayed, some inquiring grad student will be stunned by the number of prions they unearth in a random soil sample of the unidentified burial site."
Now, a recent study indicates that prions could be made more infectious via certain soils. From the University of Wisconsin, Madison, Christopher Johnson et al. tested prions' ability to bind to different minerals that could then be orally transmitted to grazing animals. They published their results in PLoS Pathogens. According to the study, transmissible spongiform encephalopathies (TSEs), (which include BSE, scrapie in sheep, and chronic wasting disease) not only survive in some soils, but because prions selectively bind to certain minerals, might be more infectious in mineral laden clays.
Researchers in another study found that prions remain in biowaste after sewage treatment. Glen T. Hinckley and fellow scientists at University of Wisconsin published research in ASAP Environmental Science and Technology (via Nature News) showing that prions survive activated sludge treatment and anaerobic sludge digestion that's used to degrade waste in waste water treatment plants.
Lurking on Your Portabellos?
Nature News suggested forebodingly that we should assume prions are in biosolids leftover from wastewater treatment, and since "biosolids are often used as crop fertilizer, this raises the prospect of small amounts of prions being present on the surfaces of the crop plants - and without careful washing, they could therefore be ingested when the food is consumed." (Taken at face value this is bad and good. Bad for obvious reasons. But think how much less work grad students would have to do in gathering their specimens? -- straight from the dining hall salad bar to the bench.)
But really? Prions on your crudités? So far prions have not been found in wastewater, only in biosolids, and aside from the current research they haven't ever been found in routine tests -- although the authors of the wastewater paper point out that the the tests aren't sensitive enough to detect them. Prions would occur at very low levels since they are rarely found in humans, so the possibility that they would somehow end up on salad is not impossible, but according to an EPA scientist interviewed by New Scientist is quite remote. She added that alkaline treatment used by some treatment plants, though not the Madison one, would deactivate the prions.
Prions are know to be resilient to conditions that would kill viruses and bacteria, but studies have also shown prions sensitive to extremes in PH. For instance researchers found that prions that mice were less susceptible to prions than cows, because mice digestive systems contain greater amounts of hydrochloric acid. Authors of the first paper above hypothesize that when prions attach to minerals in soil this might protect them from acid and explain their enhanced ability to infect the host.
