Mule deer bucks are often the first animals affected by CWD when it is introduced to a region, possibly due to their heightened movements and socialization with other animals.

By Nick Simonson

A good number of movies about diseases – Outbreak, Contagion, Pandemic, even Dawn of the Dead – have made it into the top ten on Netflix in recent weeks as fear and curiosity, along with free time have spurred a desire to understand how diseases spread.

And, like with Hollywood’s tales, in real life, outbreaks often start with just a spark of infection in a single patient.  It is just as possible that the spark smolders and dies out, taking with it only its host before it can be spread to any other member of the species.  Other times – as evidenced over the last 60 years with Chronic Wasting Disease (CWD), a neurological disease caused by a prion (a sort of misfit, folded protein with incredible longevity) that essentially eats holes in the brain tissue of cervids like deer and elk – the spark finds kindling in the form of other hosts to infect, and begins to blaze a trail of destruction through the population.

With CWD now present throughout the upper Midwest and south central Canada, and several positive tests in 2019 adding to the cases detected in North Dakota since 2009, the disease is at the forefront of the North Dakota Game & Fish Department’s (NDG&F) big game management issues. According to NDG&F Wildlife Veterinarian Charlie Bahnson, D.V.M, that relative ease of transmission through saliva, feces, urine and other bodily fluids of deer, and the ability of CWD to stay on the landscape through those means, is fueling the flames of an epidemic that threatens the future of deer hunting across the country.

“It was first recognized in a research facility in Colorado in the 1960s and then a number of years later they started recognizing it in wild deer in the same area,” Bahnson relates as to CWD’s most likely origins, “where exactly it originated is uncertain, but that’s where we first saw deer infected with the disease, it was this curiosity for a number of decades, but starting in the late 1990s and early 2000s, it was seen in more and more states and more and more areas and was paired with a higher infection rate,” he added.

Once CWD is introduced into an area – through transport of live cervids, or the bodies of harvested deer, moose, or elk – it remains present on the landscape and spreads.  Those places with higher deer densities have seen a greater prevalence of CWD in their herds, and a faster spread, to the point where it is beginning to impact populations.  The always-fatal disease, at its worst, could be picked up by a fawn shortly after birth, limiting the deer’s lifespan to an average of around 20 months.  This in turn can impact the number of mature deer on the landscape, ultimately decimating the number of older bucks and does available for harvest, and create continuous population damage, both in terms of numbers and quality, year-after-year, like a non-stop series of bad winters, according to Bahnson.

“We’re early in that process, there’s other parts of the country where prevalence will easily be 20 to 30 percent, and I’ve anecdotally even heard of populations where you’re looking at 60 percent of hunter harvested deer [being infected] within localized areas,” Bahnson explains, “some of our eastern states that are dealing with CWD are looking at deer densities of 40 to 50 to 60 deer per square mile, that’s just a lot of susceptible individuals in a small area, it’s a recipe for rapid spread; in most of our area of North Dakota, we’re at four to six deer per square mile,” he relates, suggesting that is one major factor in helping slow the spread of the disease among the state’s herds.

At this time, the CWD trends observed in other states with both whitetail and mule deer are playing out across the northern prairie.  In samples taken from hunter-harvested deer in North Dakota during the 2019 rifle season, nine mule deer bucks came back positive out of the 12 total animals with CWD.  Where the disease is established, it began predominantly with the male mule deer in the region and then the does, before leveling out in the whitetail deer population shortly thereafter until it was fairly even across both species and their genders. 

While there may be physiological factors in play, Bahnson hypothesizes that mule deer bucks, with larger territories and potentially more contact with other animals, are more likely to get infected due to their heightened activity across the landscape. Currently, it is estimated by the NDG&F from hunter-harvested samples taken in unit 3F2 last year in south central North Dakota, that three percent of the mule deer population likely has CWD, and just under one percent of whitetails in the area are infected. In northwestern North Dakota, positive samples from dead deer on the landscape and taken from hunter-harvested animals have been found in units 3A1, 3B1, 4B and 4C.  Where the disease goes from here is up to sportsmen.

“The ship has not sailed yet in North Dakota, we have a real opportunity where – yeah, we have it – but collective action now means that we can keep this thing at bay in the long term,” Bahnson states, “other areas that have those alarmingly high infection rates, in all honesty, their options are pretty limited,” he continued, adding that sharpshooter teams, herd reduction tactics and other means of removal in those eastern states are about all that can be used to lower the population densities and slow the spread of CWD, with an extreme cost to agencies and taxpayers in terms of dollars, and to sportsmen in terms of lost hunting opportunities.

Sportsmen serve as the firebreak against the flames of CWD and while now that it is established in the region and will likely not die out, there are ways to prevent it from flaring up in the near term and impacting the hunting opportunities of future generations.  Hunters are encouraged to become familiar with transport regulations designed to prevent the spread of CWD and to avoid using bait to attract deer to hunting areas which would create a point where bodily fluids are easily transferred between animals.

Hunters should familiarize themselves with the NDG&F’s Regulations on CWD and obey the laws in place in those areas affected by the disease and the units adjacent to them which have baiting and other restrictions set up to slow the spread of the disease.  For more information, visit: gf.nd.gov/wildlife/diseases/cwd.