Research on hunter-harvested mule deer in Wyoming has shown that in herds where CWD has been present the longest, a growing percentage of deer have developed a genetic trait that makes them more resistant to the disease.
February 10, 2023
By Jason Snavely
Last month, I covered some details on exactly how Chronic Wasting Disease (CWD) operates , including its transmission pathway and its lengthy incubation period. This month, I’d like to take a look at some of the more promising but underreported research concerning this important topic. There is no shortage of scientific literature on CWD, but now a handful of researchers are focusing on some extremely promising avenues to provide us with a hopeful snapshot of how nature will manage this in the long run.
Genetic Resistance One aspect of CWD that experts often mention is how the disease is always fatal. Certainly, this is true if we are talking about individual animals infected with disease-associated prions and the hallmark, progressive neurological degeneration that leads to a gradual loss of body function. However, I hardly believe the presence of CWD at the population level means an end to whitetails. In fact, when I consider the latest research and its long-term implications, I believe evolutionary biology and disease-driven natural selection will step in and manage the disease. Let me explain.
Just like everything in nature, genetic adaptations occur at a very slow rate, as in over the course of hundreds or even thousands of years. This concept is hard to understand for those of us living in a society that tends to focus on instant results, but the good news is that the longer CWD infects deer herds, the more scientists learn about how genetic adaptations affect the prevalence and impact of the disease at the population level.
Remember, the scientific community has only known about CWD for 55 years, but even in that short time there is evidence to suggest that in wild mule deer herds where the disease is known to have been present the longest, nature is already responding in a positive way. And there is no reason not to believe a similar process isn’t underway among whitetails and other cervids (elk, moose, caribou, etc.) susceptible to the disease.
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University of Wyoming researcher Melanie LaCava and her associates have conducted CWD tests and genetic sequencing on hunter-harvested mule deer. In mule deer herds where CWD has been present the longest, researchers found a common allele (genetic mutation) that slows the progression of the disease. Although the mutation was found in samples taken from throughout the state, it was more common in the areas of the state where CWD has been present the longest; natural selection is at work!
These findings suggest individual deer with this “slowed progression” will remain reproductively active longer and produce offspring that will also possess the same allele. Deer with this genetic trait were also less likely to test positive for CWD. From a long-term perspective, it’s not hard to see a scenario where does can pass this particular allele and detectable levels of CWD to their fawns, allowing those fawns to live longer and produce fawns of their own.
Interestingly, this was not the first scientific look at this genetic phenomenon, and prior results were strikingly similar. Researchers have been studying CWD-related gene mutations for many years now, but it’s exciting to know that several leading researchers are sharing similar findings.
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It is also worth noting this research is good evidence against alarmist claims of a whitetail version of the zombie apocalypse that will wipe out entire populations from coast to coast. Such scare tactics always make me laugh, considering that most free-ranging whitetails never live past three years of age due to a combination of hunter-induced and natural mortality that has nothing to with CWD. When you consider that the incubation period for CWD can be two years or more before symptoms appear, and then throw in a beneficial genetic mutation that could extend that even further, you are now talking about animals that are adapting to survive longer than most animals in a hunted population do already!
Selective Breeding Although natural selection takes a long time to play out in nature, that process can be shortened with man’s help. Recent genetic research in captive whitetail herds has revealed the existence of disease-resistant prion protein variants. Critics quickly point to the fact that this research is done in highly controlled deer-farming facilities where managers can speed up nature’s gradual changes through selective breeding of individuals. This is true, but I consider it an accomplishment, as we are able to see where nature is headed with CWD-resistant whitetails right before our eyes.
Other new research is looking at the entire genome of the whitetail, allowing researchers to study genetic differences between deer that test positive and deer that test negative for CWD. By identifying genetic differences between the two groups, researchers are able to predict which specific animals possess traits that help protect them from CWD and which ones possess traits that make them more susceptible. This area of research is challenging, but it’s great to know some really talented people are working on it and already seeing promising results.
Vaccines I was recently told by a leading CWD researcher that if he could choose which chapter he would write in a book about CWD, he would choose vaccines, because it would be a very short chapter! The truth is, there are none , and even if there was a successful vaccine that protected a significant portion of the population, you would have to deliver it to most of the individuals in the wild. This is not feasible. The vaccine would likely need to be delivered orally through a supplemental feed and ironically, most state agencies cite feeding and baiting as a disease-spreading practice.
Research on CWD vaccines thus far has actually shown that survival of vaccinated elk was significantly shorter than unvaccinated elk. Vaccinated animals have been shown to exhibit a seven times higher infection rate when they were administered a research vaccine. Yes, you read that right!
Next month, in the final installment of this series , I’ll dive into some of the research on whether humans can become infected by eating venison from CWD-positive animals. I’ll also discuss the various management approaches to CWD and cover which ones seem to be working, if any.
