By Mark Hall

Op-Ed Commentary

Genetic clues in the fight against Chronic Wasting Disease

Chronic wasting disease (CWD) has become one of the most pressing wildlife health issues in North America. Hunters, conservationists, and scientists alike are grappling with its spread across deer populations, and the debates around how best to respond are as heated around campfires as they are in academic conferences.

Alberta was hit hard when infected deer moved westward from Saskatchewan, and now the disease has crept into southeastern British Columbia. The arrival of CWD in the extreme west of Canada underscores the urgency of finding solutions that balance science, management, and public values.

At the heart of the conversation lies a controversial question: should hunting and culling be used to reduce deer densities, thereby lowering transmission rates? Some argue that fewer deer means fewer opportunities for infection. Others recoil at the idea of widespread culling, seeing it as too harsh or ethically troubling. Yet amid these debates, a fascinating frontier of research is emerging—genetics.

Dr. Alfred Roca, professor in the Department of Animal Sciences at the University of Illinois, has spent years studying genetic variation in wildlife. Alongside colleagues, he has uncovered striking evidence that certain genetic variants in white-tailed deer dramatically reduce the impact of CWD. Unlike most diseases, where genetic resistance might shave off a few percentage points of risk, these variants appear to offer reductions of 66% with one copy and up to 90% with two copies.

The key lies in the prion protein gene. Prions are misfolded proteins that can trigger other proteins to misfold, leading to transmissible spongiform encephalopathies—diseases that literally leave sponge-like holes in the brain. In deer, this manifests as altered behavior, thirst, and congregation around water sources, which in turn accelerates transmission. But mutations at positions 95 and 96 of the prion protein seem to change the structure in ways that make deer far less susceptible.

Illinois provided fertile ground for this research. Since CWD entered the state in 2002, the Department of Natural Resources has collected thousands of samples from hunted deer, sharpshooting operations, and even vehicle collisions. By matching positive and negative deer from the same square mile, researchers could isolate the genetic differences. The results were clear: deer carrying the advantageous variants were far less likely to test positive.

What makes this discovery even more intriguing is its prevalence. In Illinois, about 43% of deer carry one of these protective variants. Similar studies in Alberta found nearly half of sampled deer had them as well. That’s unusually high for a disease first identified in 1967. Roca speculates that something in the distant past may have driven these variants to higher frequencies, perhaps an ancient epidemic that selected for resistance.

Yet not all populations are equally fortunate. The endangered Colombian white-tailed deer of Oregon and Washington, genetically isolated from other herds, show no protective variants at all. If CWD reaches them—as it already has in neighbouring Idaho—the consequences could be devastating. By contrast, Florida’s Key deer, another isolated subspecies, are remarkably protected, with more than 90% carrying advantageous alleles. These stark differences highlight how genetic isolation can either safeguard or imperil populations.

Genetic resistance isn’t unique to CWD. Epizootic hemorrhagic disease (EHD), another viral threat to deer, shows similar patterns. In the southern United States, deer populations appear to have developed resistance over time, while northern herds remain highly vulnerable. Outbreaks in British Columbia and Washington have left deer “tipping over all over the landscape,” as one hunter described. Roca’s team has investigated immune system genes, such as toll-like receptors, which recognize viral shapes and activate defenses. Variants in these genes may explain why some deer survive EHD while others perish.

So, what does this mean for wildlife managers? Traditionally, CWD strategies have focused on reducing deer densities to limit contact and transmission. While effective, this approach ignores the underlying genetic makeup of populations. If nearly half of deer in a region carry protective variants, indiscriminate culling could inadvertently remove individuals with the very traits that offer hope for long-term resilience.

Understanding genetic resistance opens new possibilities. Managers could monitor allele frequencies across landscapes, identify vulnerable populations, and tailor strategies accordingly. In isolated herds like the Colombian white-tailed deer, genetic data could inform urgent conservation measures. In more connected populations, managers might balance density reduction with efforts to preserve genetic diversity.

Of course, genetics is not a silver bullet. Deer with advantageous genes are not immune; they can still contract and shed prions, albeit at lower rates and over longer lifespans. There are also questions about whether longer-lived deer with the advantageous genes might contribute more prions to the environment. Current evidence suggests this is unlikely to outweigh the benefits, but ongoing research is essential.

The story of CWD is one of complexity: a disease spread by proteins rather than viruses, transmitted through soil, plants, and water, and resisted by mutations that may have roots in ancient history. It is also a story of hope. The fact that protective variants are already widespread in many populations means that natural selection could gradually shift deer herds toward greater resilience.

For hunters, conservationists, and policymakers, the challenge is to integrate this genetic knowledge into practical management. That means moving beyond a one-size-fits-all approach to density reduction and recognizing that not all deer are genetically equal. It means protecting vulnerable subpopulations while allowing resistant traits to flourish in others. And it means continuing to invest in science that bridges the gap between laboratory findings and field realities.

While density reduction remains a tool, genetics provides a deeper layer of insight that could shape more effective, nuanced, and hopeful strategies. By combining traditional management with genetic awareness, we stand a better chance of safeguarding North America’s deer populations against one of the most insidious wildlife diseases of our time.

To listen to the full interview, check out the Alberta Conservationist Podcast: Genetic Resistance to Chronic Wasting Disease || Ep. 4 with Dr. Alfred Roca. 2025. Available of Spotify and Apple Podcasts under the Hunter Conservationist Podcast channel.

– Mark Hall is the Executive Director of The Wild Origins Canada Foundation and host of the Hunter Conservationist Podcast.

e-KNOW file photo

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