October 31, 2018
By far the largest threat to our future deer populations, and deer hunting, is chronic wasting disease (CWD). Recently, there have been several very important scientific reports on this terrible disease.
First, the good news. Veterinarians and biologists in Wyoming and Colorado released data from a 10-year study to determine if CWD is transmissible to cattle. They used two approaches: inoculating calves orally with brain tissue derived from CWD-infected mule deer, and housing cattle for 10 years in a captive cervid research pen that formerly housed CWD-positive deer.
Two groups of cattle were housed for 10 years in pens where infected deer had lived. They also had daily contact with known and potentially infected mule deer or elk, yet no cows got CWD. After being euthanized, none had lesions — or disease-associated prion proteins. The same for cattle that were inoculated. The authors conclude that cattle risk from CWD is very low.
More good news. Last year, some Canadian and German scientists released data from a study started in 2009 that showed that macaque monkeys got CWD from eating venison from deer that had CWD. However, sample sizes were very small. Even so, alarm spread from these data indicating that perhaps humans were more susceptible to CWD than once believed.
Well, time to rest a bit easier, because a National Institutes of Health study showed that macaque monkeys do not get CWD. Fourteen macaques were cerebrally and orally exposed to brain matter from CWD-positive deer and elk. After 13 years and extensive tests, no monkeys showed any signs of CWD.
I don’t know why the results of these two studies differ, but I’m going with the NIH study because the sample sizes were large, and the study ran for 13 years.
We know that prions can remain viable for many years, but how many? We do not know. So, they could be in our bodies from eating CWD deer or elk, and not become infective for years. What is needed is a long-term study that follows the lives of humans who have eaten CWD-positive meat (and there are hundreds of thousands of such people). After 20-30 years, do such individuals get a prion-like disease? It turns out that there are such studies being done, but as I’ve noted, it will take decades to see if we are susceptible to these prions.
Two recent reports show that hunters appear to be playing a role in the spread of this disease. There are no data to actually prove that hunters are spreading the disease, but knowing how it spreads, two hunter activities almost certainly are moving CWD into new areas.
The first report comes from Lindsey Thomas of the Quality Deer Management Association. In an April 2018 article published on the QDMA website, Lindsey took a very unique approach in looking at the home zip codes of over 32,000 hunters who harvested deer in the 2016-2017 deer season in the four counties in Wisconsin with the highest incidence of CWD. Many of those deer were infected with CWD. In fact, Lindsey noted that CWD incidence in bucks in these counties is 15 percent, 42 percent, 45 percent, and in one region of the fourth county it is 51 percent. So, hunters are taking a lot of CWD bucks.
Although most were killed by Wisconsin residents, a lot were taken by nonresidents. As you might expect, the states with the most nonresident hunters who hunted in those four counties were ones closest to Wisconsin — Minnesota and Illinois, followed by Michigan, Iowa, Indiana, and Ohio. But there were some successful hunters from California, Florida, Georgia…all over. Every state except Delaware had hunters in those four Wisconsin counties. Why does this matter?
We know that CWD is spread by body parts of deer. That’s why 11 states do not let their hunters bring in deer parts that have high-risk tissue (brain, spine, skull cap if any brain tissue is on it, spleen, lymph nodes). In other words, your deer must be butchered before you bring it home in those states (MN, AK, CA, AZ, LA, AR, MO, IL, IN, NY, ME). Another 22 states have the same rules if you shoot a deer from a state that has CWD. Only nine states have no importation rules for hunter-killed carcasses. (For info on your state’s rules, go to ncwildlife.org/Hunting/Cervid-Carcass-Regulations).
We know darn well that many nonresident hunters bring deer back home without being butchered first. Surely, some of these deer have CWD. For those who butcher the deer themselves, what do they do with the bones, skull, etc.? Into the garbage can and landfills? If so, that probably minimizes the spread of CWD. Discard it in the woods? That could easily spread the disease. Why don’t the state conservation officers arrest the hunters who illegally bring whole deer or elk carcasses back to their home state? They try to. But, how do you stop and check all hunters, on all major highways entering a state? It’s impossible, so the only way this really is effective is if the hunters take responsibility here.
Kudos to Lindsey Thomas and the QDMA for this innovative analysis, and to the North Carolina wildlife agency for posting regulations on this issue for every state.
One last study. Wisconsin scientists found 11 mineral licks in the wild in an area in Wisconsin with high incidence of CWD. Ten of these were places where hunters placed a mineral block, and one was a natural site. As you know, over time the block deteriorates and minerals get into the soil. After the block is gone, deer still come and lick the soil, or drink the water that accumulates in depressions that form there. The results showed that soil from seven sites had prions. They also sampled water from nine of these sites, and six had prions. Two of the licks had prions in both the soil and water.
At the site with the highest detection of prions, they sampled 10 fecal pellet droppings and six were positive for CWD prions. One conclusion made is that mineral sites may be reservoirs for spreading CWD. That seems fairly obvious, and the fact that CWD-positive deer dropping fecal pellets near these sites further exacerbates the problem.
There are those hunters who feel that CWD is not a problem. The reasons are many, but the science doesn’t serve them well. Hunters need to listen to the trained biologists doing research on CWD. They understand the significance of a growing amount of science that shows how disastrous CWD can be for deer hunting. For those who read this column, you’ll keep getting the science.