CWD Prions Discovered in Scrapes?

Chronic wasting disease continues to march across the country. Despite intensive efforts to learn more about this always-fatal, prion-based illness, slowing the spread has proved challenging at best. Florida was recently marked as the 32nd state to harbor CWD. But that isn’t the only recent news.

Researchers discovered measurable volumes of CWD prions in scrapes. Image by Russell Graves

Recent Research

According to the National Deer Association, Miranda Huang of the Mississippi State University Deer Lab widened eyes at the Southeast Deer Study Group’s annual meeting, held in February.

Her research detected CWD prions in scrapes. The sample size included 99 monitored scrapes, each of which were in a CWD zone in southwestern Tennessee. She tested each scrape for prions using RT-QuIC technology. Deer shed CWD prions in various ways, including urine, feces, saliva, and other bodily fluids. So, Huang took soil samples from the scrape on the ground and clipped licking branches overhead.

Of the tested scrapes, 54 of 99, or about 55%, tested positive for CWD prions. Further, 35% of the licking branches and 14% of the soil samples tested positive. About 6% of the scrapes tested positive on the licking branch and in the scrape. Unsurprisingly, a buck that was captured on trail cameras overlooking some of these scrapes was killed by a hunter and subsequently tested positive for CWD.

NDA also reported that another study in northern Mississippi discovered CWD prions in scrapes. However, no harvested deer had yet tested positive in that area.

What It Means

Because RT-QuIC technology lets biologists test for CWD without sampling live or dead deer, wildlife agencies are considering using the innovation with scrapes as a means of CWD surveillance and monitoring prevalence. It won’t replace the testing of harvested deer but will serve as an additional tool.

In theory, the confirmation of CWD prions in scrapes supports the claims that indirect transmission is possible. It now seems more likely that direct deer-to-deer contact — breeding, grooming and going nose to nose, for example — isn’t the only way deer spread the disease.

The low prevalence of prions in the soil indicates that urine poses a lesser risk of spread, though. Although 55% of scrapes harbored CWD prions, most of those were found on the licking branch (via saliva) rather than in the soil (via urine or feces). That should reassure scent companies, wildlife agencies, and deer hunters that scent lures pose a low risk. That’s even truer given that most states only permit the use of Deer Protection Program- and RT-QuIC-approved scent products.

All things considered, the discovery of prions in scrapes isn’t a giant revelation. More appropriately, it’s a confirmation of expectation. However, the ability to test scrapes for prions will help state wildlife agencies monitor the spread of the disease. Further, it could confirm pre-existing beliefs that deer are possibly transmitting CWD indirectly via scrapes.

After all, deer are social animals, and CWD will spread via the various direct and indirect encounters deer have with each another. If you factor in how 50% to 75% of bucks disperse up to 15 miles from their birth areas, as do some does, it’s difficult to envision how humans might halt the CWD onslaught.

Despite multi-agency efforts, it isn’t likely we’ll stop the spread. Nature will continue to carry prions into new places. Currently, other than limiting the movement of captive deer and harvested deer parts (wild or otherwise), there isn’t much we can do. CWD has us on our heels, and that won’t likely change soon.

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