Chronic Wasting Disease
The North Dakota Game and Fish Department has been concerned about chronic wasting disease for a long time.
The invariably fatal disease can cause long-term population declines and the effort to test for it in North Dakota began in 1998 with roadkilled, sick and suspect animals. In the early 2000s, the Department increased CWD surveillance efforts by annually collecting samples from hunter-harvested deer, elk and moose.
A brainstem from a hunter-harvested deer to be sent in for CWD testing.
During that time, 15 deer have tested positive for CWD in the state – 13 from Grant and Sioux counties in the southwest, and one from Divide County in the northwest – starting in 2009.
The 15th animal, a severely emaciated white-tailed deer found dead just south of Williston in late February, was the first documented case of mortality due to CWD in North Dakota.
Following the positive results of the Williston whitetail, the Game and Fish Department collected additional samples from 52 deer in the same area through targeted removal. All samples tested negative for CWD.
Deer hunting in North Dakota is a big deal. Hunters, no matter if they are packing archery equipment, high-powered rifles, or both, take their hunting seriously, and show great interest in the health and management of the state’s whitetail and mule deer populations.
With the deer gun and muzzleloader application deadline set for June 5, North Dakota OUTDOORS staff visited with Dr. Charlie Bahnson, Game and Fish Department wildlife veterinarian, about CWD and the Department’s continued efforts to manage North Dakota’s big game populations threatened by the unwelcome disease.
Q: Why is the Department concerned about CWD?
A: There are several reasons to be concerned about CWD, but at the top of the list is what more and more studies are starting to find. If the number of animals infected with CWD in a population reaches a certain threshold, it becomes a major cause of decline in the population. At low infection rates, CWD can be dismissed as a curiosity. At high infection rates, it can become a catastrophe. It is the threat of someday reaching that point in areas of North Dakota that keeps me up at night.
Q: After the white-tailed deer was found dead south of Williston in February and tested positive for CWD, Game and Fish decided to collect additional samples for testing through targeted removal. Why was targeted removal employed in this instance and not when deer tested positive in Grant, Sioux and Divide counties?
A: Our previous positives have all been animals harvested before they became sick, and they were mostly adult bucks, as was the case with all three found during the 2018 hunting season. These animals move across the landscape a lot, making it hard to say exactly where they came from. In contrast, the Williston deer was a mature doe that appeared in a semi-urban environment. The deer may have gone through the whole course of the disease – infection to death – in a relatively small geographical area. Other states have found high rates of infection within female family groups, so there was a strong reason to suspect that we were dealing with a localized hot spot of CWD. But ultimately, we needed more information to know how big of a problem we had on our hands.
Q: Fifty-two deer were taken during targeted surveillance efforts near Williston. Why this number?
A: Thirty adult deer was the minimum amount we needed to make a reasonably accurate estimate of the prevalence of CWD within that area. This gets at a core concept in epidemiology. You can’t say much about how common a disease might be in a population if you only test a few animals. Maybe it is rare, and you just didn’t happen to sample the positives. As the number you sample increases, you start to gain more statistical weight. Of the 52 animals, 29 were adults and 23 were yearlings or fawns. That was the minimum we needed to get an estimate in that area.
Q: Fortunately, samples from those deer taken by targeted removal near Williston all tested negative for chronic wasting disease. What do you make of these results?
A: The results were really a best-case scenario. We know that CWD is now in the area, but we aren’t dealing with the potential hot spot of disease that we had feared. It does raise more questions in my mind about the initial positive doe. Where did she come from? Was she a local or did she wander in from somewhere else? We are working to develop some laboratory tools to answer questions like this and we collected DNA samples from all the deer we sampled in this area.
Q: Why wasn’t the venison salvaged from those animals?
A: We weighed that decision very heavily, but in the end, the cons outweighed the pros. Going into a disease investigation, you must assume that all animals are positive until proven otherwise. As a result, we had to go to great lengths to get all carcass parts off the landscape and contained until results were received 10 days later. And in sampling that many deer in a laboratory setting, we couldn’t maintain a level of cleanliness that most people would approve of. I am a hunter who takes wasting meat very seriously, but I am also a veterinarian who swore an oath to protect the health of animals and the public. We didn’t know what we would find, and we had to plan for the worst. In the end, I think we made the right decision.
Q: How does North Dakota compare in terms of prevalence of CWD to other states and provinces where the disease is an issue?
A: If there is any positive note in this issue, it is that North Dakota is still in a position where we can keep this under control. There are populations in other parts of the continent where the prevalence is 30-40 percent, or even higher. That means 30-40 percent of your deer have a terminal disease that cannot be eradicated. That’s a tough situation. In hunting unit 3F2 in the southwest, our prevalence is closer to 1 percent. That is a rate we can live with, but we must be proactive.
Q: You’ve said we need to do everything in our power to ensure that finding sick or dead CWD-infected deer doesn’t become common like in other areas of the country where CWD has reached a tipping point. What are some of the things we can do to safeguard North Dakota’s deer population?
A: First and foremost, we need hunters to keep hunting. Hunters are the primary tool for managing healthy wildlife populations in North Dakota. But in addition, this really does take a lot of self-reflection about what we as hunters may be doing to increase the risk of spreading CWD from one animal to the next. CWD can be spread directly between animals, but also indirectly through contaminated environments. Deer congregate naturally for a portion of the year and we can’t do much to change that. However, we make that worse by increasing the number, duration and intensity of those congregations by baiting throughout late summer and fall. We also know that the movement of infected carcass parts is one way to introduce the disease into new areas. The Department has implemented transportation regulations and bans on hunting over baits and has made other recommendations that are found on our website. Whether these things will help slow the spread of CWD depends heavily on how willing our hunting community is to adopt them. This is a tough battle that requires a long-term commitment, but if you look at the past 10 years in 3F2 where we have maintained a low prevalence of CWD in conjunction with decent hunting opportunities, there is reason to be optimistic moving forward.