This Iowa County white-tailed deer may have felt safe standing beside a No Hunting or Trespassing sign.
CWD is mentioned about as often as DNR and IRS. What is this thing hunters, politicians and wildlife biologists argue about and call chronic wasting disease?
Chronic wasting disease, or CWD, is a fatal brain disease of deer, elk and moose. While the disease has been known to exist in several western states for several decades, it first showed up in Wisconsin deer in 2002. It could have been here several years before that.
CWD is one of several transmissible spongiform encephalopathies, simply called TSEs. The name says these diseases can be transmitted and make holes in the host organisms' brains. Of course the host dies.
Mad cow disease in cattle and Creutzfeldt-Jakob disease in humans are several related diseases, in that they are caused by abnormal prions, too.
Three deer that were killed by Dane County hunters during the 2001 season tested positive for CWD and those results became known in February 2002. These tests were conducted during the last phase of statewide surveillance testing of Wisconsin's deer. All wild deer in other regions of Wisconsin tested negative for CWD at that time.
This year, in addition to continuing to test deer for CWD in areas where CWD is known to exist, Wisconsin is beginning another round of surveillance testing. Deer killed by hunters in northeast Wisconsin are being tested this year; next year the west central region will be tested.
First the disease. Unlike colds caused by viruses, strep throat caused by bacteria and athlete's foot caused by fungi, CWD is not caused by a virus, bacterium or fungus.
Animals have normal prion (pree-on) proteins associated with nervous tissue and when an animal gets one of these prion diseases some prion proteins take on an abnormal shape and cause problems and eventually death.
It can only be determined for sure that a deer has CWD if a piece of the nervous tissue is sampled and tested. There are quick, preliminary tests and more accurate tests that take a week or more to conduct. The quick tests rule out positive tissues, but all suspect samples are retested using a slower, more accurate method.
The misshaped prions in deer can be passed on to other deer in the population through direct contact and possibly by other means, such as from contaminated soil and maybe by a doe to a fetus in her uterus. There is not a vector involved, it seems, such as a mosquito or tick that carries the disease from deer to deer.
There is no cure for CWD once an animal has the disease. Virtually all deer in Wisconsin's population are probably genetically susceptible to CWD if they are exposed to it by one of the transmission methods.
There is no evidence that CWD can cause a disease in humans, but it makes no sense to consume venison from animals that had the abnormal prions in their nervous tissue, because the deer could have secondary infections that could be lethal.
The primary method of managing CWD in Wisconsin has been to reduce the number of hosts (deer) in areas where the disease is known to exist. In theory, if there are no hosts, there can be no disease. Also, the fewer hosts, the less likely infected animals will transmit the disease to other animals.
While there is much scientists do not know about CWD, it is misleading to say we don't know enough to deal with CWD. That would be like saying we don't know everything about cancer, so we can't try to manage it. The same might even be said about the common cold, too.
It is possible that our fetish for deer had a great deal with CWD entering Wisconsin. Captive deer have been brought into and moved around Wisconsin for years. A number of captive deer have tested positive for CWD.
It may be that if we want any deer in the future, we're going to have to accept having far fewer deer and making sure the deer we do have remain wild rather than trying to domesticate Wisconsin's state wildlife animal.