column By: Jack Ballard | July, 18
A reliable source tipped me off the day before the news went public. The Montana Department of Fish, Wildlife and Parks had discovered chronic wasting disease (CWD) in a mule deer buck shot some 15 linear miles from my front yard. A short time later, another muley buck tested positive from the same area. A whitetail doe about 25 miles farther north was also confirmed as a CWD carrier. By the end of the general big-game hunting season in 2017, CWD had not only been established as present in Carbon County (south-central Montana) but had been discovered in a mule deer in the north-central portion of the state as well.
Game management personnel and other informed observers were not surprised when Montana was toppled from its presumed “CWD-free” status, and it certainly came as no shock to me. CWD was known to be present in Wyoming, not far south of my home in Carbon County. It had also been confirmed close to the Montana border in Wyoming and not far away in the Dakotas. To the north, Alberta and Saskatchewan had verified cases of CWD in free-ranging deer just north of the state. The thought that every disease-carrying deer curtailed its travels at the state borders was patently ridiculous. The discovery of CWD in Montana wasn’t, as the old saying goes, “a matter of if, but when.”
Nonetheless, its confirmation pricked this hunter with a new awareness. I’d researched the disease in 2004 in relation to a deer hunt in southern Wisconsin shortly after CWD was discovered there. At that time it was assumed that the best approach to management was the attempted elimination of as many deer as possible from the infected area. Hunters were also reassured that the disease posed no threat to humans, as the “species barrier” from ungulates to Homo sapiens was deemed insurmountable.
As we kept tabs on the CWD saga in our own county, my wife, Lisa, was researching the disease for an article in a national magazine. Her inquiry came to include interviews with Montana’s foremost authority on the disease, and Bryan Richards, the emerging disease coordinator for the USGS National Wildlife Disease Center, the nation’s leading expert on CWD. A lot has changed since 2004.
Foremost in our minds was recent research indicating the “species barrier” between cervids (members of the deer family) and humans in relation to CWD may not be as impervious as once thought. In brief, CWD is not a “disease” in the sense of a foreign organism like a virus or bacteria that attacks a creature’s body. It is, rather, a transmittable spongiform encephalopathy, also called a prion. A prion is essentially an abnormal protein that creates structural abnormalities in certain types of living tissue. CWD is comparable to bovine spongiform encephalopathy (mad cow disease) in cattle and scrapie in sheep.
Over time CWD prions become more concentrated in the central nervous system of the infected animal but are also found in other parts of its body. It is always fatal, though it is visually undetectable in infected animals until shortly before death. From infection to fatality, the progression in deer normally takes around two years. The abnormal prions in the brain and nervous system eventually impair the creature’s ability to function normally, even in relation to such simple tasks as eating.
Can humans contract CWD?
Although it hasn’t been confirmed, several recent studies have tipped the answer in the minds of some experts from “no” to “not so sure.” “There’s no evidence that CWD has crossed to humans, but research says there’s a chance. Lots of folks think I’m an alarmist, but the research also suggests the species barrier is not as robust as it was once thought,” said Bryan Richards. Those studies included one in which researchers exposed brain matter from deceased humans to CWD prions that resulted in conversion to prion abnormalities. In another from Canada, macaque monkeys were fed CWD-infected venison. Two of the macaques became afflicted with the disease. It is also known that mad cow disease (a similar prion disease) has leaped from bovines to humans as Creutzfeldt-Jakob’s disease. At the present time, the U.S. Center for Disease Control and the World Health Organization strongly discourage consuming meat from CWD-positive animals.
So what’s a hunter to do? First of all, it’s advisable to understand the prevalence or possibility of CWD in your hunting area. The USGS website (www.nwhc.usgs.gov/disease_information/chronic_wasting_disease) has mapped known locations of the disease in North America. Understand that the map only shows places where the disease has been confirmed and maps it by county. Thus, a positive test for an animal killed a mile from the county line will show up only in its county of detection. Also realize that state agencies have widely varying programs of CWD monitoring and in many cases do not have the financial or human resources to thoroughly scout for the disease. “Unconfirmed” does not necessarily imply “not present.” Thus, hunting within a reasonable distance (I would say 30 miles) of a CWD-positive area means that at least a small percentage of cervids (deer in particular) could easily carry the disease.
Hunters should also be acutely aware of the fact that the appearance of an animal, short of obvious CWD symptoms, gives no indication of its status. Noticeable clinical symptoms do not appear until the final weeks of the two-year incubation period. However, some of the neurological aberrations that eventually kill the animal probably occur sooner, while the animal still looks healthy.
It is known that CWD-positive deer are preyed upon at higher rates by predators and are more likely to be killed in automobile collisions. One study in southeastern Wyoming also concluded they are shot by hunters at disproportionately high rates. Just prior to exhibiting clinical symptoms, it is possible the animal’s ability to recognize environmental threats (such as humans and cars) is impaired. Thus, in a CWD-positive area, the fact a hunter was able to kill a “not so smart” buck possibly means it is more likely to be an infected deer. Researchers have also found that CWD-positive bucks are less likely to participate in the rut.
In relation to physical precautions, much remains as it has for years. Use rubber gloves when field dressing an animal. Avoid handling the spinal tissue, brain and lymph nodes where CWD prions are most concentrated, although they also reside in meat and elsewhere in the body. Have the animal tested and do not consume the meat if it’s positive. Dispose of the carcass of a CWD-positive animal in accordance with your state game agency’s recommendations, and never toss it back into the wild where it will shed prions.
On a final note, it is no exaggeration to state that chronic wasting disease could cause the extinction of some local deer herds (especially mule deer) within a few decades. Investment in research and monitoring is key to combating its effects. This is an area where government investment – in the form of tax dollars or higher license fees earmarked for CWD research – is critical for detection, research and management. Chronic wasting disease now significantly affects my local hunting. Odds are high that it’s coming to your location if it’s not already there.