Posted on 04/16/2006 11:19:58 PM PDT by neverdem
Scientists have confirmed that prions, the mysterious proteins thought to cause chronic wasting disease (CWD) in deer, latch on tightly to certain minerals in soil and remain infectious.
The discovery that prions stay deadly despite sticking to soil comes as a surprise, because while many proteins can bind to soil, that binding usually changes their shapes and activities.
In a paper published in the journal PLoS Pathogens (April 14), scientists at the University of Wisconsin-Madison suggest that certain soil types serve as natural prion repositories in the wild. As animals regularly consume soil to meet their mineral needs, it's possible that prion-laden soil particles contribute to the transmission of prion disease such as CWD among animals.
CWD is a fatal, incurable condition that belongs to a family of prion-inflicted neurological disorders known as transmissible spongiform encephalopathies (TSE). Other TSEs include "mad cow" disease, sheep scrapie and Creutzfeldt-Jacob disease in humans.
After a long incubation period, deer and elk infected with CWD suffer neurological and behavioral problems such as staggering, shaking, and excessive salivation and urination. Over time, the animals literally waste away, often dying in woods and fields. Originally detected in the 1960s in Colorado and Wyoming, CWD is now present in 14 states and two Canadian provinces.
Prions are an incorrectly folded variation of a protein normally found in mammals, including humans.
"Prions most likely enter soil via excretion or from the carcasses of infected animals," says lead author Christopher Johnson, a UW-Madison doctoral student in the department of animal health and biomedical sciences. "Our results suggest that reducing the number of infected animals -- as has been done in the recent outbreak of CWD in Wisconsin -- could limit the potential for further (disease) spread. These results also suggest that other species that share ranges with CWD-infected deer may be exposed to soil-bound prions, increasing the potential of CWD transferring to other species."
This may just be the case. Last year, Colorado authorities documented the first known instance of CWD in a wild moose, a species previously not known to be susceptible to CWD. How the moose became infected is unknown. The known range of the disease continues to spread eastward from where it was first discovered in Wyoming and Colorado to deer-rich states such as West Virginia, where CWD was first detected last September.
Using a variety of laboratory procedures, the UW-Madison team measured the affinity of prions to three common soil minerals: quartz, kaolinite and montmorillonite. The infectious prions, they found, bind tightly to montmorillonite, a type of clay found in soil.
"We also wanted to determine how difficult it is to remove prions from clay," says senior author Joel Pedersen, a UW-Madison assistant professor of soil science. "It turned out to be extremely difficult."
In fact, prions could be released from clay only when the scientists boiled the clay-bound proteins in a detergent solution.
To ascertain whether prions remain infectious in soil, the researchers also injected clay-bound prions into laboratory animals. The animals began to show TSE symptoms at approximately the same time as animals injected with only prions.
"That result indicates that interactions with the clay mineral do little to reduce prion potency," says co-author Debbie McKenzie, a senior scientist in UW-Madison's School of Veterinary Medicine. "Knowing that prions could be maintained in the environment makes it important to continue removing as many CWD-infected deer as we can," she says.
"While injecting clay-bound prions into experimental animals has shown that they remain infectious, more environmentally relevant exposure routes need to be examined," says Pedersen. Experiments examining oral infectivity are under way. The researchers also plan to determine how long prions remain infectious in soils.
The Wisconsin team indicated that while their results may provide some new insight into how prion diseases such as CWD are transmitted, there are many questions that have yet to be answered about how animals acquire the disease.
Judd Aiken, a professor in the UW-Madison School of Veterinary Medicine, and Kristen Phillips and Peter Schramm of the UW-Madison Molecular and Environmental Toxicology Center, also participated in the new study.
The article is available in PLoS Pathogens; unlike other scientific publications, a subscription is not required to access this journal at: http://www.plos.org/press/plpa-02-04-pedersen.pdf
This is the crux of the matter. If clay bound prions can be effectively removed from the food chain by adsorption onto clay minerals, then certain soil types will make preferred pastureage for domestic animals should the CWD be shown to be capable of interspecies infection.
It might be possible, through the use of soil amendments to help keep those prions bound by pH controls, although having to boil them and use detergent to separate them sounds like the prions are in a fairly stable arrangement.
I hope they also study what mechanisms, if any release the prions in the digestive tract of the animal, whether it be enzyme action, stomach acids, or a combination (or other factors).
Scrapie has been rumored to remain in the soil for a long time and be capable of infecting sheep later.
I've noticed this website just recently. Does anyone have any feedback with respect to their political orientation?
Has any one read about F. O. Bastian and his Spiroplasma hypothesis for TSEs at PubMed? Enter Bastian FO, and spiroplasma into PubMed
What about blowing dust from a construction site? Does it contain dangerous prions?
FReepmail me if you want on or off my health and science ping list.
Documented BSE in cattle herds here is extremely rare.
In the event that the land had been used to graze sheep, and that there was scrapie known in the flock, it is possible that prions are present in the topsoil, but I would expect the construction company has removed the topsoil where any prions would be likely to be, and the blowing dust is the (generally lighter colored) mineral soil base below. The topsoil is often conserved for reapplication after landscaping when construction is complete, or may be used at another jobsite.
That, I would expect, would not be heavily contaminated (if at all), even if all other conditions had been met, simply because of the relative lack of orgaincs present (which generally accounts for the lighter color).
Note, too, that some mineral soils are deposited in environments which were swampy, and will be dark colored (usually blue-gray) as well. If there are light yellow brown or rusty colored nodules in the soil (ranging from marble sized to sometimes several feet across) usually the minerals limonite or hematite--AKA 'bog iron') and the soil is gray to blue gray in color, it usually indicates a swampy origin.
Overall, I'd figure the odds were against contamination by prions from dust blowing off the site. (Although that can be one heck of a nuisance).
It appears the author may be on to something.
In another abstract, it is postulated that the Spiroplasma bacterium and the prion (if I am reading it correctly) act as the two components of a binary infection mechanism, with the one getting the other into the cell to cause infection.
Thanks hardly seems appropriate after such a thoughtful and informative reply. Thanks very much. Much appreciate the information.
Spiroplasmas, not Prions, are Likely Cause of TSEs
CJD Diagnostic and Research Center
You are most welcome. Apparently, there is an alternative hypothesis to the origins of CWD and other TSEs, but the likleyhood of the infectious agent in that instance being present in blowing dust from a construction site would be about the same, for the same reasons.
The more I read about Spiroplasma, the more likely it seems to be a causative agent. I would like to see more inquiry (which takes funding) along those lines.
And just for the record, I am a geologist, and do not have any interest in the allocation of research funding beyond wanting to be able to go deer hunting without any reservations.
I'm going to bookmark this thread. You've got an interesting discussion going and I hope it continues.
Thanks for the ping.
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