COVID-19 – Lessons in CWD Management for Deer Hunters

COVID-19 – Lessons in CWD Management for Deer Hunters

What the current coronavirus disease (COVID-19) response around the world has taught us are the basic biological principles that influence the risk of disease transmission among individuals. The principles used in the COVID-19 response are useful to better understand how to manage a disease like Chronic Wasting Disease (CWD) in deer (including white-tailed deer, mule deer, and elk). While the two diseases and the infectious agents that cause them are totally different, they share a few similar characteristics of transmissibility that offer useful lessons on how to manage our way through them.

An elk herd in Colorado

Deer live in a natural world where inclement weather, poor nutrition, predators, and disease are risks to the survival of the animal. Biologists and many deer hunters work year-round to improve the environment and health of deer herds. Diseases (e.g. Epizootic Hemorrhagic Disease and Bovine Tuberculosis) have become more prominent as threats to deer populations – especially the prion-based disease, CWD. Thus, hunters would be prudent to take note of how human actions have, and are, impacting the current pandemic of virus-based COVID-19, and apply those lessons to the management of CWD in their state or favorite hunting area. There is little doubt that if humans were not modifying their traditional social behaviors, COVID-19 would rapidly increase in infection and disease-related health impacts. Similarly, if hunters remain unwilling to make adjustments to some of their traditional hunting behaviors, CWD, like COVID-19, will readily take advantage of our collective lack of diligence.

Social distancing, for instance, means deliberately increasing the physical space among people to avoid spreading COVID-19 infectious material. Human family units are being asked to shelter in residence and avoid interacting with other families and coworkers to reduce the potential of COVID-19 spread. Therefore, social gatherings and large crowds are discouraged or prohibited. By government order, restaurants and bars are closed in many places to prevent social gatherings that could increase disease spread. When thinking about this in the context of CWD and deer, this is akin to removing bait and feed piles (like closing crowded restaurants where individuals concentrate) and other practices that concentrate deer in a small area where disease transmission risk is dramatically increased.

Quarantining involves stopping or limiting movement of infected individuals or potentially exposed individuals. Humans are being asked to minimize or eliminate long distance travel and to self-quarantine for 14 days upon arrival to minimize the risk of establishing new COVID-19 disease focal areas. Stronger prohibitions on travel are in place in some places, such as closing borders to human movement from other countries/states. A parallel in CWD management would be hunters or cervid farmers being asked to not transport intact deer (living or harvested) or certain carcass parts from one place to another to minimize moving CWD prions (infectious material) from infected areas to uninfected areas, and to properly dispose of any remains once processed.

Although COVID-19 is now found throughout the world and the U.S. regardless of human density, COVID-19 hot spots are more likely in higher density urban areas, large factory settings, or other areas where human-to-human contact is greater than in rural areas. In CWD management, susceptible animal populations should be kept at or below carrying capacity, as determined by a combination of biological and social factors, throughout the year to minimize spread of disease. When managing CWD, reducing deer density in areas where the number of deer is elevated can be an important tool to reduce the interaction of animals congregated into smaller portions of their range such as wintering areas or fawning areas (especially where habitat is limited) at various points of the year.

Many human diseases often disproportionately affect one portion of a population more than another. During the 1918 Spanish flu epidemic, mortality was high in people younger than 5 years old, 20-40 years old, and 65 years and older. Older adults and people of any age who have serious underlying medical conditions are at a higher risk of serious illness from COVID-19. These differences provide clues to scientists working to develop COVID-19 surveillance and response strategies in humans. In deer, CWD occurs at nearly twice the rate in older males than other segments of the population. Thus, CWD management actions directed at eliminating or reducing infected animals would be most effective when directed at a population segment like older age-class males that persistently hold the highest prevalence of the disease.

When most of a population is immune to an infectious disease, this provides indirect protection—or herd immunity (also called herd protection)—to those who are not immune to the disease because the proportion of the population that is not immune is so low that it is difficult for the disease agent to spread. Doctors have successfully used vaccinations or exposure to the disease to create herd immunity for many diseases such as measles, mumps, polio, and chickenpox. Some have suggested application of this approach to COVID-19. Herd immunity works if an effective vaccination is successfully administered to a high enough proportion of the population to slow or stop disease spread. Without a vaccination, another approach is to let the disease sweep through the population and accept that a percentage of infected people (or any other animal) die. Currently, researchers don’t yet know the mortality rate of COVID-19, but many believe it to be too great to consider letting COVID-19 simply sweep through the population.

Unfortunately, herd immunity doesn’t apply to CWD in deer because the infectious agent is a non-living protein, not a virus like COVID-19. Therefore, unlike COVID-19, CWD is 100 percent fatal to all susceptible animals; all infected individuals will die. And while some research has shown that genetic differences in deer may slow the progression of the disease, all infected individuals eventually die.

Testing is key to managing all disease. Without it, researchers and managers have little hope of combatting disease spread and identifying effective treatments. Response to both COVID-19 and CWD has been slowed by the lack of available test kits and the logistical and financial costs of administering them. Epidemiologists and biometricians can determine necessary sample sizes if, and only if, the research or management question that is needed to be answered is understood. Just doing more samples may be a waste of resources if not necessary to answer the question. For example, are you testing for early detection and management of new infections? To slow spread of existing infections by infected individuals and their contacts? To determine overall incidence of infection in a population? Etc. All call for different testing procedures and sample sizes. Thus, it is important for management of both diseases that the reason for testing is articulated by those calling for more or less testing. Hunters should be prepared to submit samples when state officials request participation to inform management responses.

Though COVID-19 and CWD are vastly difference diseases, human reactions to how the diseases must be managed and the impacts those actions have on behavioral norms are strikingly similar. CWD and COVID-19 are both highly infectious diseases that thrive when susceptible individuals interact closely with one another. Additionally, they share similarities in how human behaviors must be disrupted in order to effectively combat and control the diseases. Staying home, avoiding contact with others, and working from home are difficult mandates that have caused resistance and backlash as agencies and governments attempt to flatten COVID-19’s infection curve. Increased adult buck harvest, sharp reduction of deer density, restrictions on feeding or baiting, restrictions on carcass transportation, and testing requirements have likewise been difficult for hunters to accept as wildlife management agencies seek to flatten and control CWD infection in deer, elk, and moose populations.

Similar to the current COVID-19 outbreak, normal activities have been and will be disrupted during management of an emerging CWD outbreak. The most difficult concept about managing for a disease in wildlife is that proactively taking steps to prevent a disease from occurring is hard to do because humans are creatures of habit who want to continue doing traditional normal activities. Once the disease is found, policies should be put in place to change those traditional activities that exacerbate the disease to a new normal. Much as we have witnessed in the COVID-19 response by society, people will want to support and comply with good policy if we want to flatten the curve of the impact of CWD on deer herds.

Photo Credit
Vince O'Sullivan, Flickr
May 15, 2020