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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Extended hunting seasons and sharpshooters try to further reduce the deer herd in areas where CWD has been detected. © DNR Photo
Extended hunting seasons and sharpshooters try to further reduce the deer herd in areas where CWD has been detected. © DNR Photo

October 2005

Three years down
a long road

Controlling chronic wasting disease remains a work in progress.

Robert E. Rolley


Wisconsin's CWD management plan
Results to date
Human health issues
Research and public discussions
Containing disease spread
Changes at game farms
Be prepared for a long-term commitment

The discovery of chronic wasting disease in southern Wisconsin back in February 2002 was a significant moment and a serious threat to our state white-tailed deer population and our deer hunting culture. Here, all things deer remain a favored pastime and a big business. Wisconsin's more than 700,000 deer hunters annually harvested an average of 460,000 deer during the last decade. The deer hunt provides more than seven million days of outdoor recreation each year and boosts the state economy with more than $500 million in retail sales each year and nearly $1 billion for the state businesses when travel, lodging, food, clothing, equipment and deer processing are added to the economic mix. Whitetails are also important to nonhunters who enjoy seeing deer. In 2001, an estimated 2.2 million residents watched wildlife and nearly 300,000 visitors made trips here to observe wildlife, especially deer.

We know now that chronic wasting disease (CWD) is not a wildlife disease that will simply run its course and die. Wildlife disease experts have concluded that CWD will not naturally burn itself out if left alone. The abnormal proteins (prions) we believe cause the disease persist in the environment. Currently there are no proven treatments or vaccines for prion diseases and all infections are believed to be fatal. CWD will most likely increase in prevalence and distribution without management intervention. Further, there is no evidence of genetic resistance to CWD in white-tailed deer or mule deer. Computer models that simulate how diseases spread suggest if the disease were left unmanaged over the next 10-30 years that it would spread widely and might infect more than 40 percent of adult deer.

Though there are no instances of CWD infecting people, many hunters remained concerned because of similarities between CWD and mad cow disease (BSE). If CWD infections are found more often and over a more widespread area, the disease could surely decrease interest in hunting and in eating venison. Hunters who have been surveyed told us that if CWD infects more than half the herd, more than half the current hunters would stop hunting. Those numbers would drop even more if scientists ever confirm a link between CWD and human disease.

Wisconsin's CWD management plan

Given so many scientific uncertainties about the basic biology and ecology of CWD, our efforts to manage the disease are experimental by nature. There just aren't established protocols and proven solutions for stopping this disease, but we need to do what we can to contain it and we can't wait for new research before we act. Since CWD behaves in a manner that's similar to other infectious diseases, it's reasonable that some of the techniques used to manage these other chronic diseases may work for combating the spread of CWD. We'll keep trying new strategies that look promising, but we'll also keep evaluating the effectiveness of controls by a very practical test – is the disease infecting more animals or fewer animals, and can we slow its spread into new geographic areas? That's why intensive surveillance for the disease remains an important tool.

When chronic wasting disease was verified in Wisconsin whitetails, we quickly realized that we'd need a plan that looked at wild animals, domestic animals, human health and we'd need research in all of these areas. We developed an interagency partnership among the departments of Natural Resources; Agriculture, Trade, and Consumer Protection; and Health and Family Services; together with the University of Wisconsin; U.S. Department of Agriculture; and the U.S. Geological Survey's National Wildlife Health Center and Cooperative Wildlife Research Unit.

Our aim is to minimize consequences for wild deer and elk, captive herds, hunters, landowners and others whose livelihoods depend on these herds. Our strategy to take steps to eradicate CWD in southern Wisconsin was endorsed as sound and laudable, though ambitious by an independent panel of wildlife disease experts in April 2003. That stance was reaffirmed this last July at a worldwide CWD summit held in Madison.

Managing a disease in a free-ranging wild deer herd will remain controversial, difficult and expensive – controversial because it depends on reducing the deer herd significantly. We're not sure if it's possible and some landowners in the Eradication Zone remain unconvinced of the need; difficult because deer are spread over a wide area, they continue to breed and control efforts may have to continue for decades; expensive because the only reliable way to evaluate disease spread is to test large numbers of deer, and tests are both time-consuming and costly.

Results to date

Surveillance for CWD in Wisconsin started in 1999 upon the discovery that infected elk from game farms in the western U.S. had been transported to other states. Through the fall of 2001, about 1,100 deer bagged by state hunters tested negative for the disease. Three positive samples from western Dane County were harvested during the November 2001 hunt and disease was confirmed in test results reported in February 2002. That warranted more intensive testing in March and April 2002. Some 516 deer were collected within a 12-mile radius of the three positive samples. Fifteen of those deer also tested positive for CWD. More extensive testing has continued since that time. As of last April, 470 wild deer have tested positive for CWD; 445 of those in southwestern Wisconsin, 24 in three counties nearer the Illinois border, and one in eastern Dane County between the two outbreaks. Just south of the border in adjacent areas of Illinois, another 96 deer have tested positive for the disease.

Recent late winter aerial surveys monitor deer population changes in the Disease Eradication Zone (DEZ). © DNR Photo
Recent late winter aerial surveys monitor deer population changes in the Disease Eradication Zone (DEZ).

© DNR Photo

The disease outbreak in southwestern Wisconsin is tightly clustered and not random. More than 80 percent of the infected deer detected were found in a 126-square-mile area bounded by Spring Green, Mazomanie, Black Earth, Mount Horeb and Ridgeway. In that core, 4-5 percent of the deer have tested positive for CWD, at the center of the core in a few sections of land, 8-12 percent tested positive. The infection rate appears higher in bucks than among does and is higher in older animals than in younger ones.

Human health issues

There's no evidence that CWD has ever caused illness in people. As a caution, health experts do not recommend eating known CWD-infected animals, especially those tissues like brain, spinal and lymph nodes where prions are shown to accumulate.

The departments of agriculture and natural resources continue to work closely with meat processors to revise butchering procedures to remove tissues where prions accumulate. Hunters also have easy access to guidelines for processing their venison to minimize risk of CWD exposure.

Hunters in the disease eradication zone of CWD-affected areas can also request to have their deer tested free of charge. A simple system alerts hunters of those test results. When deer have tested positive, the hunter will receive a phone call; for negative tests, hunters receive a post card. Results are also quickly posted on a website. Elsewhere in the state, hunters can have their deer analyzed for CWD with the help of veterinarians and diagnostic labs.

Systems for disposing of deer carcasses and butchering wastes have also been developed to minimize disease exposure. Research shows that sanitary landfills can adequately contain these wastes, yet, due to concerns from landfill operators and municipal waste managers, more stringent disposal options have been taken for the past three years. Awaiting test results, DNR wildlife managers store these deer in refrigerated semi-trailers. Animals that test positive and butchering wastes are incinerated or chemically digested.

Last year another option made better use of animals harvested by hunters who did not choose to keep them for their own use. Over 2,200 deer that tested negative for CWD were processed by Wisconsin meat packers into one-pound packs of ground venison and were donated to food pantries. Through this cautious approach, hunters are now keeping or donating better than 85 percent of the deer harvested.

Research and public discussions

Thirty-four CWD studies are underway in Wisconsin and we're collaborating on another 12 studies nationwide to answer questions about how the disease, deer and people interact in the environment. Others are testing tools for diagnosing the disease and determining any human health consequences from CWD exposure. There are lots of practical questions to answer about how the disease is transmitted; how prions react in soil; determining which animal species are most susceptible to the disease; and evaluating how hunters, landowners and others react to CWD news. Research on diagnostic tests for CWD have already led to new screening tests that significantly shorten the testing notification time for hunters who harvest deer.

Public outreach to notify people about CWD investigations has also gotten more sophisticated. Wildlife managers use a mix of public meetings, newspaper articles, maps, public opinion polling, personal visits, toll-free information lines, individual mailings, web pages, publications and contacts at registration stations to share information. A majority of hunters surveyed believe they are receiving enough information about chronic wasting disease to make sound decisions about disease exposure and about two-thirds believe the agency provides opportunities to listen to their concerns and opinions about the disease. Moreover, communications among the Department of Natural Resources, other state and federal agencies, researchers, landowners, hunters, municipalities, lawmakers and other residents in areas where CWD is being investigated is critical in taking collaborative actions to control the disease spread.

Containing disease spread

Removing as many deer as possible from CWD-infected areas provides our best opportunity to control the disease. Since there are no effective CWD vaccines nor proven treatments for infected animals, a key strategy remains reducing the deer herd size and changing its composition. Increasing the harvest, especially of does, will eventually produce smaller herds of younger animals. That's important because we know that younger animals are less likely to transmit the disease; deer over three years old have the highest infection rates. As the population size drops and fewer deer disperse, disease transmission would also be expected to drop.

We're coupling that with other strategies to reduce disease spread. Within counties where CWD has been identified, sick, injured and "orphaned" deer cannot be rehabilitated. The sale and movement of farm-raised game is carefully monitored. All deer harvested or dying on game farms must be tested for signs of the disease. And butchering wastes and carcasses are carefully managed as previously described. Baiting and deer feeding within CWD areas is prohibited to lessen the likelihood that deer will congregate and potentially spread disease. In areas where CWD has been detected, extended hunting seasons and bag limits will remain much more liberal and additional permits will allow landowners to hunt deer outside of established seasons. Some landowners have allowed government sharpshooters to remove additional animals in late fall and winter months.

A partnership with Whitetails Unlimited in 2003 and 2004 offered rewards to hunters and landowners who harvested deer that subsequently tested positive in CWD affected areas. Hunters and landowners split $400 payments when positive deer were detected and all hunters who registered deer taken in the disease eradication zone (DEZ) were eligible for $20 payments drawn on a lottery basis. An estimated $250,000 was paid out each year under this incentive program.

These combined programs are slowly reducing herd numbers in infected areas as hoped. In 2002-3 more than 9,200 deer were removed from the eradication zone, nearly 13,700 deer in the 2003-4 season and approximately 16,000 in the 2004-5 season. Between 65-70 percent of these animals were antlerless deer (does and fawns). A survey of hunters in the DEZ following the 2003 season found they hunted an average of four days longer and harvested twice as many deer as hunters outside of the CWD management zones. Still, the goal of reducing the deer densities in CWD affected areas remains daunting. Researchers believe they will need to reduce and sustain the herd levels to about five animals per square mile of deer habitat to control the disease. Winter aerial surveys estimate cumulative efforts since 2001 have reduced the herd 40 percent from 48 to 28 deer per square mile in Deer Management Unit 70A that is entirely within the DEZ. A similar Herd Reduction Zone sets a 40-mile radius ring around the DEZ in southwestern Wisconsin within which managers provide hunting opportunities to reduce deer populations to 10 deer per square mile. Between 73-75 percent of the deer harvested in this zone were antlerless deer in the last three years.

Changes at game farms

Nearly 720 deer and elk farms in Wisconsin contain about 30,500 animals – mainly whitetails and elk with smaller numbers of several other deer species. Since the discovery of CWD these farms have been subject to more recent inspection and more rigid bookkeeping requirements. They've had to beef up their fencing and testing programs. Orphaned and injured deer from the wild can no longer be accepted at game farms. All farms selling live animals must census their animals, mark each with identifying marks and file annual reports detailing where each animal came from or was shipped. Any animal imported into Wisconsin needs a permit from the State Veterinarian, certified inspection, proof that it is free of tuberculosis and brucellosis and documentation that it came from a herd that has had no evidence of CWD for at least five years.

DNR audits of 550 farms in 2002 found the majority complied with existing state laws, though 77 game farms had fencing violations. Audits showed that during the lifetime of those game farm operations more than 400 animals had escaped from more than 182 farms.

Currently 544 of the 720 captive herds are enrolled in the monitoring program. The remainder are small hobby farms or hunting preserves that do not ship live animals. All captive animals 16 months or older that die or are slaughtered must be tested for CWD. As of last February, 29 farm-raised white-tailed deer and one elk have tested positive for CWD from seven different Wisconsin farms. All the animals from five of these seven herds have been destroyed and the owners indemnified. One owner is contesting the court order and the animals in question remain under quarantine.

Be prepared for a long-term commitment

Public support to eliminate or contain the spread of CWD remains strong among hunters and landowners. Support for the particular strategies the Department of Natural Resources is pursuing is not as strong, but most give the DNR good grades for the efforts to date. Commitment from the general public and legislature will be critical to bolster the $20 million (largely from hunting fees) spent in Wisconsin since 2002 on CWD surveillance, management and eradication efforts. We believe the average $5 million spent annually on CWD management is a sound investment to protect the health of our deer herd, given deer hunting's nearly $1 billion impact on the state's economy and its value as prized recreation.

We can't accurately predict how many years it may take to determine if CWD control programs in Wisconsin are effective in reducing the incidence of disease and the size of the area affected. However, our nation's experiences in controlling other animal diseases are instructive. U.S. programs to eradicate brucellosis in the nation's beef herd began in 1934. The infection level was reduced from 11 percent in the 1930s to five percent in the 1940s to less than one percent in the 1970s. The Australian programs to eradicate bovine tuberculosis and brucellosis required over 20 years. Michigan's program to eradicate bovine tuberculosis from its free-ranging deer herd has been underway for 10 years and may require another 10-20 years as well.

During these first three years of dealing with this disease we've conducted extensive tests to determine the extent of the disease. We've made significant progress reducing free-ranging deer populations where disease has been detected. We've taken further steps to reduce its transmission including banning baiting and feeding of deer in these areas, and tracking and controlling CWD spread on game farms. We've also made significant headway in describing the realistic risks of disease exposure to people, setting up systems to test harvested animals, sharing those results, safely disposing of deer that test positive, and making good use of deer that are not infected.

Given how much we have to learn about this most unusual disease, it's too early to predict whether our management program can eradicate CWD, but that is clearly our aim. Stopping any wildlife disease, especially one that is caused by abnormal proteins, is a difficult challenge. Our management approach is very similar to that which is making headway in Michigan to control bovine tuberculosis. Controlling CWD in one of our most popular and widespread wildlife species will test our resolve, our financial commitment, our staff and volunteer commitment, and our scientific abilities to limit its spread. This effort will also require sustained cooperation and communication among natural resource and agricultural agencies, researchers, volunteers, hunters, landowners, and captive deer/elk producers.

Robert E. Rolley is a wildlife researcher with DNR's Bureau of Integrated Science Services.