CWD: a moving target

Efforts to eradicate, suppress chronic wasting disease must be aggressive

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Arkansas' Rotnei Clarke (left) and Stefan Welsh in the closing seconds of their 77-64 loss to Georgia at the Southeastern Conference tournament in Nashville.

Published in 1949, Aldo Leopold's Sand County Almanac ended with a chapter on what he called the "land ethic," which he said "enlarges the boundaries of the community to include soils, waters, plants, and animals." He said that these entities together are collectively known as "land."

Today, the land is facing the spread of a disease for which there isn't a cure. In the year 2000, Chronic Wasting Disease (CWD) was declared a national emergency by Congress, and in 2003, congressmen allocated between $17 million and $19 million per year through 2012 to undertake what they considered a surveillance of deer populations in states where CWD had been found in either captive of wild ungulate populations.

What has been found has not been pretty.

"The issue is very, very challenging," said Bryan Richards, emerging disease coordinator of the USGS National Wildlife Health Center of Wisconsin, in a discussion concerning the nationwide spread of the disease.

When CWD was found in wild deer populations in Wisconsin in 2002, the state's Department of Natural Resources (WDNR) enforced an aggressive push to eradicate the disease.

"The WDNR expanded hunting seasons and landowner opportunities to harvest deer, distributed unlimited harvest tags, employed agency sharpshooters, and vigorously promoted efforts to dramatically reduce the deer population in the affected area in an attempt to disrupt disease transmission," wrote Richards in an email conversation.

But the public pushed back hard against the tactics. Left with fewer options of mitigation, WDNR simply continued to monitor the herds. What WDNR officials found was that in the area hardest hit by CWD, 40 percent of adult male deer have become infected over the past 12-year time span. The statistics were similar to those found over a 15-year span in western Wyoming, an area where CWD was endemic early on.

"Given time, CWD can rise to 40 to 50 percent prevalence levels (in deer populations)," said Richards. "At that point, it will lead to population impacts."

But he explains the population impact could relate less to outright die-off and more to the fact that CWD will limit the lifespan of does, which in turn will limit the birth of offspring as female deer often give birth to twin fawns in their later years.

"And now there are tests that show that prions bind to plants. Even when they are washed and dried, the prions are still there," said Richards. The prions Richards refers to are the deformed proteins that cause CWD.

In addition to studies discovering that prions bind to plants, two new studies released earlier this year from Wisconsin's National Wildlife Health Center (NWHC) and from the University of Texas Health Science Center at Houston (UTHealth) found plants have the ability to take prions into their root systems from the soil. The prions can then move to the stems and leaves of plants.

According to an article from the Wisconsin Academy of Sciences, Arts and Letters, researchers at NWHC have found that prions can be taken up from the soil by plants such as alfalfa, corn and tomatoes.

AT UTHealth, the team found the same outcomes in wheatgrass roots and leaves. When the wheatgrass was in turn fed to hamsters, the animals were infected with the disease.

"If we've got (CWD-positive) deer urinating and defecating in fields, then if we are moving those commodities across state lines, we've now got another plausible mechanism for the spread of the disease," said Richards.

Right now, there are 23 states that are battling CWD in wild and captive deer populations. The spread was initially thought to be fairly slow moving, limited to environments where deer gathered, then gradually radiating out via natural roaming habits of wild cervids. But with human intervention, the circumstances seem to be changing.

Mike Miller has been studying CWD for over a decade. Located in Colorado where the disease was endemic by the mid-1990s, Miller is the senior wildlife veterinarian for the Colorado Parks and Wildlife Health Program.

"My general sense is that natural geographic spread is relatively slow and somewhat predictable," he said. "But human activities like moving infected animals can lead to much more rapid and unpredictable spread."

That is why wildlife officials and departments of natural resources across the country are increasing limitations on the movement of animals by both hunters and by breeders.

But humans don't always do as they are asked. According to a September press release by the U.S. Fish and Wildlife Services, a Georgia man was fined $1.6 million for trafficking white-tailed deer that had not been certified to be disease-free. It was the largest sum of money ordered of an individual to pay for a wildlife crime in the United States.

In the state of Missouri, deer breeders must register their herds with the Missouri Department of Agriculture if they intend to move or sell their animals. Under that program, if any deer dies in a registered facility, it must be tested for CWD.

If breeders do not register their deer, but move the animals anyway, they could face charges under a federal law that prohibits the illegal transport or sale of wildlife.

One local breeder currently faces such charges. Sam James, part owner of Timber Hollow Whitetails located in Callaway County, currently has charges pending for an illegal state-to-state sale of captive deer to a Florida facility in 2013. Attempts to reach James for comment on these charges were not successful.

"The majority of these business owners are meticulous, careful and follow rules," said Richards. "But there's always a dark side to every business, and those are the ones who pose a risk."

As they become more aware of the risks surrounding CWD, scientists begin to understand the disease has a further reach than anticipated when it was first discovered decades ago, and they are calling for increased pre-emptive measures.

"Early, relatively aggressive and sustainable control efforts seem the key to suppressing Chronic Wasting Disease," wrote Miller.

Richards echoed that opinion.

"You must take strong preventative measures to keep the disease from coming to you," he said. "Because if it does, you are going to be dealing with it for a very long time."