Dueling Over Disease: The CWD Debate

September 13, 2015 By Gordon Whittington

Dr. James Kroll explains Chronic Wasting Disease in whitetails in this Dr. Deer segment from NAW TV.

There's rarely a lack of disagreement between wildlife agencies and whitetail hunters. Of course, that's nothing new; hunters have been complaining about season lengths, bag limits, appropriate equipment and much more for as long as there have been game agencies to put restrictions on hunter behavior.

But it isn't always just hunters who disagree with agency decisions. Sometimes it's other members of the wildlife management community.

Chronic Wasting Disease (CWD) is a case in point. Even now, nearly a half-century after this deadly deer and elk disease showed up in Colorado, and after untold millions of dollars have been poured into research and control measures, we still know frustratingly little about CWD's origin or even how it's transmitted.

But what we do know is that some harsh measures are being tried in an effort to stop CWD from spreading.

CWD has become a serious issue in many states. From 1999-2012, about 1,800 deer tested CWD positive in Wisconsin alone.

Based on the theory this disease might become established in new areas via commercial deer urine, several states recently have banned the use of such products within their borders — regardless of origin or means of processing. Predictably, this move has angered many scent companies, retailers and sportsmen. But what might be surprising is that it's also drawn criticism from at least one renowned CWD researcher.

Dr. Nicholas Haley, a research veterinarian at Kansas State University, is widely regarded as one of the world's top authorities on CWD transmission. And in a recent open letter, he called bans on urine-based hunting products into serious question. According to Dr. Haley, there are a number of far more likely means by which the disease can be spread into areas currently regarded as CWD-free.

Will banning urine-based products stop this disease from encroaching on new areas? It appears there's little hard evidence to back that viewpoint. So even after untold millions of dollars have been spent on CWD research, we're really still almost at Square 1.

No one knows how much longer it will take to come up with an effective means of control, but in the meantime, whitetail hunters in several states now are scrambling to find new ways to lure in their quarry.

Read Dr. Hayley's letter in its entirety:

Nicholas J. Haley DVM, PHD

As a veterinarian and researcher with over ten years of experience building our understanding of the transmission of Chronic Wasting Disease in deer and elk, and as the lead author on two manuscripts specifically addressing the role of urine in CWD transmission [Haley et al. PLoS ONE 2009; 4(3) and 4(11)], indeed the only two manuscripts on the subject to date, I feel this opinion would be valuable in helping guide any decisions made with respect to the trade and use of deer urine as a hunting aid.

Funding for these studies was through the National Institutes of Health, while some current funding directed towards live animal test developments for CWD have been provided by the North American Deer Farmer's Association.

My opinion is based on facts and findings from my past and ongoing research, and I will present two foundational arguments below â€“ the potential infectivity of urine in experimental and natural exposure and the caveats therein, and the further reduction of risk conferred by the mitigation steps already in place and proposed by the scent urine industry.

In the two published manuscripts covering the role of urine in CWD transmission, we found that 1) urine from CWD-infected deer, when concentrated 10-fold and inoculated directly into the brains of susceptible mice produced infection in 1 of 9 mice after protracted incubation periods (vs. a similar volume of saliva which produced infection in 8/9 mice) and 2) deer exposed orally to a large volume of both urine and feces in an earlier study (150ml-700mls urine, 150-700g feces; Mathiason et al. Science 2006) â€“ though CWD-negative by conventional IHC, were likely subclinically infected based on experimental testing.

Unpublished work (in fact, unpublishable due to current scientific constraints on publication of negative data) in deer, this time separating urine and feces, again failed to demonstrate conventional IHC detection of CWD in animals inoculated with large volumes of urine symptomatic animals.

This time, experimental, amplification-based testing in these animals was negative as well. A second unpublishable manuscript again reinforced the low levels of infectivity in urine â€“ where urine collected from 2 preclinical elk and 4 symptomatic deer produced disease in only 1 of 108 mice inoculated intracranially.

While this speaks to the very low levels of infectivity in urine, it is not far-fetched to assume other body fluids are capable of making their way into urine products â€“ saliva and feces for example, which have been experimentally shown to play a more defined role in CWD transmission.

Given these findings, there obviously remains some concern for the potential that scent urine may have some role, however small, in the introduction of CWD to new areas. The mitigation efforts currently underway in the scent urine industry I believe go a long way towards reducing this risk to nearly zero â€“ as I expressed recently in a letter to the Vermont Department of Fish and Wildlife. Farms providing urine to the scent companies have very strict standards of health to uphold:

A 5 year (at minimum) monitoring history and certification for CWD in all animals over 12 months of age, tested post-mortem. This measurement estimates, with a very high degree of certainty, that CWD is not presently in the herd. On a population level, it offers an exponentially higher level of assurance of CWD status in a given herd than most, if not all, CWD-free states can speak towards their free ranging animals. However, it is possible that CWD could be incubating at a very low level in the herd despite current negative CWD findings. This low likelihood is counteracted by each of the provisions that follow.

A regular census and health and welfare inspection required to maintain this certification. This ensures constant and close monitoring of individuals in the herd and an early indication in the case of any herd health changes.

All herds are either closed or only receive animals from other farms with the same rigorous certification history. The farmers are aware of the risk an introduction CWD has for their farm and the industry, and with these precautions it provides a very high level of confidence that CWD will not be introduced into a herd from outside, less rigorously inspected farms. Again, these steps go above and beyond what is required of typical deer farming operations, and is a much greater guarantee of health than any state, with open borders for free ranging deer and elk, can provide. (Consider the relocation of elk from Kentucky to other states without biopsy testing, for example).

Farms are double-fenced, or currently developing a second line of fencing, to prevent contact with wild and potentially CWD infected deer. This eliminates the risk of direct contact transmission â€“ which, apart from exposure to contaminated environments, is likely one of the primary mechanisms of CWD transmission in nature.

In order to prevent contamination of scent urine with feces and other unwanted and potentially infectious by-products, a number of steps have been proposed to reduce or eliminate this risk. Screens to keep out fecal pellets and food debris, maintaining feed and water outside of the urine collection pens, and avoidance of feeding during urine collection periods are just some of the mechanisms in place or proposed to mitigate this risk.

Lastly, I am currently pursuing the development of CWD resistance in farmed cervids, and trying to develop an understanding of how that might affect shedding in urine and other body fluids. The findings of this work will be an asset to scent producers and the deer farming industry as a whole, and could potentially help reduce the risk of introduction by another order of magnitude or more.

In my opnion, these efforts go above and beyond many of those used to prevent the introduction of other notable infectious diseases of economic importance, and effectively reduce the risk that scent urine might play in introducing CWD to new areas to nearly zero.

Indeed, the only point I can see these efforts breaking down are events out of their, or anyone's control â€“ a poorly sensitive test giving a false negative post-mortem result or the introduction of CWD through nefarious or unpredictable environmental routes.

Combined with the initially low risk urine carries in the form of infectivity, I strongly feel that with these mitigation steps, the scent luring industry conveys an infinitesimally small risk of introducing CWD intro currently negative areas â€“ and that other routes of introduction: dirt carried on boots or in the wheel wells of cars after traveling to CWD positive areas, predators and scavengers carrying CWD positive digesta to negative areas, water from streams and rivers traveling through positive areas down to negative areas, for example, carry a much, much higher risk of introduction.

If you have an questions or would like additional comments or clarifications, please do not hesitate to contact me.

Sincerely,

Nicholas J. Haley, PhD