Editor’s Note: this is the fourth of eight biweekly columns in which the Department of Natural Resources Secretary will try to answer some of the many questions and concerns related to Chronic Wasting Disease (CWD) in Wisconsin.
Why is depopulation of the wild deer herd in the CWD Disease Eradication Zone (DEZ) part of the DNR’s management strategy to eliminate the disease from Wisconsin?
We believe the best approach currently available to eradicate CWD from an affected area is to reduce the wild deer herd to near zero. We chose this management strategy after examining the science and consulting with CWD experts from across North America. The Multi-States Guidelines for CWD management, signed by 12 states including Wisconsin, recommends disease eradication when CWD is found in new areas and deer depopulation as the best available tool.
Depopulation is a standard disease control strategy in both domestic livestock and wild, free ranging herds in instances where neither a treatment nor vaccine is available to control the disease outbreak. In the case of CWD, depopulation removes sick animals from the landscape, reduces deer density to below the threshold at which transmission can occur, and minimizes the accumulation of CWD prions in the environment.
Targeted killing of wild cervids (deer and elk) suspected of having CWD without an accompanying effort to dramatically reduce the herd so far has failed to reduce the prevalence of the disease in Colorado and Wyoming. Wildlife officials in Colorado, where CWD was first discovered over 30 years ago, have stated that if they knew then what they know now, that state, too, would have attempted to eradicate the disease through a wild herd depopulation management strategy.
However, if we can find another strategy to eradicate CWD short of complete depopulation, we will gladly use it. As I wrote in my first column, we are using a “learn and adapt” approach to dealing with this disease. If all the research being done here in Wisconsin and elsewhere reveals an acceptable alternative strategy, I will be the first to embrace it. Until that time, herd depopulation will be the standard for eradicating the disease.
How long will it take to eradicate the disease in the DEZ?
Eradicating the disease is a long-term project. Projections by UW-Madison researchers indicate that, depending on hunter and landowner cooperation it may take as long as a decade to reduce the deer population low enough to stop CWD transmission and allow the disease to “die-out.” Without good hunter and landowner cooperation, ridding Wisconsin of CWD could take a long time and may not be possible. The scale of the job necessary to stop this disease is much greater than what DNR personnel can possibly handle alone.
Won’t intense, prolonged hunting pressure disperse deer faster and increase the spread of CWD?
All research focusing on white-tailed deer movements show that they have a strong connection to an established home range. The natural spring and fall dispersal (movement) of young deer, especially yearling bucks, is the primary reason deer move longer distances, not hunting.
There have been studies conducted in several states where hunting dogs were used to chase radio-collared wild deer and the dogs could not force deer to abandon their home ranges for more than a few days.
What we did learn here in the DEZ last fall, winter and early spring is that intense hunting pressure over a long time period makes wild deer very wary, but still did not force them to leave their home range.
If we shoot most of the wild deer in the DEZ, won’t that eliminate development of genetic resistance to CWD?
A recent UW-Madison study, which has been accepted for publication in the Journal of Wildlife Disease, suggests that virtually all white-tailed deer in this area are genetically susceptible to CWD. A team of scientists and graduate students working under the direction of Judd Aiken, a professor of animal health and biomedical sciences in UW-Madison’s School of Veterinary Medicine conducted the study. Professor Aiken is a leading authority on diseases caused by prions, the nearly indestructible proteins that cause CWD.
The UW-Madison study examined DNA from 126 infected and uninfected deer harvested within last year’s 411 square mile DEZ. The team sequenced the prion protein gene, known as PrP, from the DNA found in the cells of the deer. Although the function of the PrP protein is not known, when an animal is exposed to the disease, the normal protein converts to an infectious, disease-causing form.
Almost all of the 126 deer studied had one of the forms of the gene that are found in infected animals. The remaining deer have genotypes that are extremely rare and we just don’t know yet if they occur in infected deer.
Professor Aiken said the team’s study found that most deer in the DEZ are susceptible to the disease and although their findings don’t mean we’re not going to be able to stop the disease, they tell us we certainly cannot count on genetic barriers to slow it down.
Why not just ‘do nothing’ and let nature take its course?
It has been suggested that some deer may have a genetic makeup that makes them resistant to CWD and, if CWD ran its course through the wild deer herd, surviving animals would form the basis of a herd whose DNA would make them resistant to the disease.
Professor Aiken’s conclusion that almost all deer are going to be genetically susceptible to CWD effectively refutes that argument and lends support to our aggressive strategy of trying to eradicate CWD while we still have a chance to be successful.
A UW-Madison researcher, John Cary of the Wildlife Ecology Department, has developed a computer model of CWD in the DEZ. It suggests that CWD prevalence could reach high levels and the area’s deer population could decrease dramatically if CWD is allowed to spread unchecked for 20 years. Based on this model and the real world experience in the western states, CWD would continue to spread across the state and there would then be significant impacts on Wisconsin’s hunting traditions and economy. The UW model indicates that aggressive action in the early stages of the disease outbreak shows the best promise in preventing CWD from being established in new areas.
In the final analysis, our goal is to eradicate CWD. Regardless of the model used, we are confident that a ‘do nothing’ approach will not result in the eradication of CWD. That’s why we are heading down the aggressive path that we have chosen. We will apply what we learn as each year goes by in the hope that we will ultimately reach our goal.
Persons interested in more information on CWD and the DEZ, including obtaining landowner permits, may call the Dodgeville CWD information line at 608-935-1945.