Chronic Wasting Disease: The Latest Research
Research on Wyoming mule deer harvested by hunters has shown that in herds where CWD has been present the longest, a growing percentage of deer have evolved a genetic trait that makes them more resistant to the disease.
February 10, 2023
Last month I covered some details on exactly how Chronic Wasting Disease (CWD) works, including how it is transmitted and its long incubation period. This month I want to take a look at some of the more promising but underreported research on 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 give us a hopeful snapshot of how nature will pull this off over the long term.
genetic resistance
One aspect of CWD that experts often mention is that the disease is always fatal. This is certainly true when dealing with individual animals infected with disease-associated prions and the characteristic progressive neurological degeneration leading to a gradual loss of body function. However, I hardly believe that the presence of population-level CWD means an end to whitetails. In fact, considering the latest research and its long-term implications, I believe that evolutionary biology and disease-driven natural selection will step in and overcome the disease. let me explain.
Like everything in nature, genetic adaptations occur very slowly, over hundreds or even thousands of years. This concept is difficult for those of us who live in a society that focuses on immediate results to grasp, but the good news is that the longer CWD infects herds of deer, the more scientists are learning how genetic adaptations affect prevalence and impact disease at the population level.
Keep in mind that the scientific community has only known about CWD for 55 years, but even in that short time there is evidence that nature is already responding positively in wild mule deer herds, where the disease is known to have been present the longest way. And there’s no reason not to assume that a similar process isn’t underway in white-tailed deer and other cervids (elk, elk, caribou, etc.) susceptible to the disease.
University of Wyoming researcher Melanie LaCava and her collaborators performed CWD testing and genetic sequencing on mule deer harvested by hunters. In herds of mule deer, 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 from across the state, it was more common in areas of the state where CWD had been present the longest; Natural selection is at work!
These results suggest that individual deer with this ‘slowed progression’ remain reproductively active longer and produce offspring that also carry the same allele. Deer with this genetic trait were also less likely to test positive for CWD. From a long-term perspective, it is not difficult to envision a scenario where fawns 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 wasn’t the first scientific look at this genetic phenomenon, and previous results were strikingly similar. Researchers have been studying CWD-related gene mutations for many years, but it’s exciting to know that several leading researchers share similar findings.
It’s also worth noting that this research provides good evidence against alarming 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-roaming white-tailed deer never live past three years due to a combination of hunter-induced and natural mortality unrelated to CWD. When you consider that the incubation period for CWD can be two years or more before symptoms appear, and then introduce a beneficial genetic mutation that could prolong it even further, you are now talking about animals adapting to survive longer than most animals are a hunted population!
selective breeding
Although natural selection takes a long time in nature, this process can be shortened with the help of humans. Recent genetic research in captive white-tailed deer herds has revealed the existence of disease-resistant prion protein variants. Critics are quick to point out that this research is being conducted in tightly controlled deer breeding facilities, where managers can accelerate nature’s gradual changes through selective breeding of individuals. That’s true, but I consider it an achievement because with CWD resistant whitetails we can see where nature is headed right before our eyes.
Video that might interest you
Other new research is examining the entire genome of the white-tailed deer, allowing researchers to examine genetic differences between deer that tested positive and deer that tested negative for CWD. By identifying genetic differences between the two groups, the researchers can predict which specific animals possess traits that protect them from CWD and which traits make them more susceptible. This area of research is challenging, but it’s great to know that some really talented people are working on it and are already seeing promising results.
vaccinations
I was recently told by a leading CWD researcher that if he could choose which chapter to write in a book on CWD he would choose vaccines because it would be a very short chapter! The truth is, There are none, and even if there were a successful vaccine that protected a significant portion of the population, you would have to make it available to most individuals in the wild. This is not possible. The vaccine would likely need to be administered orally via a feed supplement, and ironically, most state agencies list feeding and baiting as a disease-spreading practice.
In fact, previous research on CWD vaccines has shown that the survival of vaccinated moose was significantly shorter than that of unvaccinated moose. It has been shown that vaccinated animals have a seven times higher rate of infection when given a research vaccine. Yes you’ve read correctly!
Next month, in the final episode of this series, I’ll dive into some research on whether humans can be infected by eating venison from CWD-positive animals. I will also discuss and cover the various management approaches to CWD that work, if any.