Editor’s Note: this is the second of eight bi-weekly 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.
How did wild deer in southwest Wisconsin get CWD?
Unfortunately, since the disease was likely introduced 5-10 years ago, we probably won’t ever know exactly how it happened. But, the more we understand about how CWD was introduced into our wild deer herd, the more we can do to prevent something similar from occurring elsewhere in the state and, for that matter, elsewhere in the country.
Starting with the discovery of CWD on Feb. 28, 2002, the Department of Agriculture, Trade and Consumer Protection and DNR’s law enforcement and wildlife management staffs began investigating the possible origins of the fatal nervous system disease found in our local deer herd. Landowners, deer farm owners, hunters, animal feed businesses and other members of communities in the CWD-affected area were contacted.
The investigation of the origins of CWD inWisconsin’s wild and captive whitetailed deer has occupied thousands of hours of conservation wardens’ time. More than 100 wardens followed up on over 500 leads and audited the records of over 600 deer farms. These investigations have added to our understanding of the activities that might have brought this disease to southwest Wisconsin, such as:
* infected deer brought into the Mt. Horeb area and released;
* infected deer escaping from a deer farm;
* hunter-harvested deer brought back from the West and carcass remains being left on the landscape;
* CWD prions made available to wild deer in deer food or mineral blocks.
People would have been unaware that CWD was present in all of the above scenarios, yet these situations all have something in common – a human activity that poses the risk of unknowingly introducing a devastating disease.
If you have information that might help us learn more about how CWD got to this area, please call 1-800-TIP-WDNR.
How do we know that CWD hasn’t been in Wisconsin’s wild deer herd all along?
We have only been testing a lot of hunter-harvested deer for CWD in Wisconsin since 1999, but for several decades we have been following up on reports of sick and dead Wisconsin deer without detecting CWD.
Last fall and winter we accomplished the most intensive CWD testing in the history of North American wildlife management. In total, we have sampled 41,245 deer statewide in an effort to get good information about where CWD is in our state.
Disease experts from the University of Wisconsin and the USGS National Wildlife Health Center have been studying the pattern of CWD cases in southwest Wisconsin. The large cluster of cases north of Mt. Horeb surrounded by a sprinkling of cases, especially to the north and west, is reminiscent of a wild fire in that there is an intense area with spot fires on the periphery. The pattern suggests there was a relatively recent (within a decade) introduction of the disease in the core area, and also suggests that, like a fire, this may be something we can put out.
What about the theory that mineral deficiency or toxicity causes CWD?
Several hypotheses about the cause of CWD have received attention recently, including the theory that high body levels of manganese (Mn), in conjunction with low levels of copper (Cu), can cause the onset of CWD. Although it may be possible such environmental factors play a role in CWD development, there are no data that support the notion that changes in Mn/Cu levels cause CWD. Very little scientific evidence has been provided to support this theory. No well-designed lab studies have been carried out to test this hypothesis.
Another hypothesis is that CWD positive deer are actually suffering from cadmium (Cd) toxicity. Cd is a naturally occurring element that is found in trace quantities in the environment. Cd has no known biological function.
There is no question that deer in southwest Wisconsin have the ability to accumulate cadmium – all animals do. And, Cd is a toxic element that can cause serious health problems. Cd concentrations have been documented in a wide variety of cervids in North America, including whitetailed deer, elk and moose. In none of these studies did liver and Cd concentrations reach toxic levels. In fact, a review of scientific literature failed to produce a single occurrence of Cd poisoning in mammals anywhere in the world.
In Wisconsin, liver and kidney tissue from a few CWD positive game farm deer have been analyzed for Cd, along with other metals. Cd was detected in three samples and levels were far below the toxic threshold.
The distribution of CWD in Wisconsin, and across North America, would also seem to refute the notion that a mineral deficiency or toxicity is responsible for these disease outbreaks. Soil, plant and animal tissue data do not support that there is something unique about the Cu/Mn or Cd levels in these areas as compared to the rest of Wisconsin or the rest of North America.
Where else is CWD in North American wild deer?
The spread of CWD in both wild and captive deer and elk populations is of great concern. In 1967, a clinical “wasting” syndrome was described in mule deer from a northern Colorado wildlife research facility. CWD has been detected in free-ranging deer and elk in northern Colorado and adjacent sections of southeast Wyoming and Nebraska between the 1980’s and 1990’s. In 2001-2002, CWD was detected in wild deer in Illinois, New Mexico, Saskatchewan, South Dakota, Utah and Wisconsin.
CWD in Wisconsin’s wild deer is of particular concern due to its potential for rapid spread within our high density deer populations. Deer densities out West are typically about two to five deer per square mile, while fall deer densities in portions of south central Wisconsin are typically in the range of 30-50 deer per square mile.
To date, CWD has been found in the wild herds of Illinois, New Mexico, Utah and Wyoming; captive herds in Alberta, Kansas, Minnesota, Montana and Oklahoma; and both wild and captive herds in Colorado, Nebraska, Saskatchewan, South Dakota and Wisconsin.