Flattening the curve of Chronic Wasting Disease in Iowa’s white-tailed deer

Everyone has learned a lot about the spread and control of infectious diseases in 2020. Although the important task at hand is to apply that knowledge in helping our neighbors and family avoid a Covid-19 infection, we would be wise to apply many of these lessons to help white-tailed deer fight a disease of their own.

Chronic Wasting Disease, or CWD, is a neurological disease affecting members of the deer family. The prion-based CWD that infects the central nervous system is a different type of disease from the virulent respiratory one we have become familiar with in 2020. But CWD and Covid-19 share many characteristics, including how they can be spread asymptomatically and the potential for high infection rates in the absence of intervention.

The fight against Covid-19 includes five now-familiar interventions; 1) wash your hands, 2) wear a mask, 3) maintain physical distance, 4) avoid large gatherings, and 5) stay home when you can. It seems unlikely a deer will soon don a mask and they have no hands to wash. So, the fight against CWD should employ three interventions.

Knowing exactly how a deer becomes infected with CWD is difficult. But, biologists know the prions that spread CWD are found in salvia and urine of infected deer. Thus, the most likely transmission route of CWD is direct deer-to-deer contact -- the deer not maintaining a safe physical distance. Because deer are highly social, convincing them to maintain physical distance is about as feasible as convincing them to wear masks. But humans can help ensure deer maintain physical distance by discouraging behaviors that lead to unnaturally close interactions. That’s why wildlife biologists espouse people to never feed deer for any reason, because packing many deer around feed or mineral is the human equivalent of packing a subway car with a bunch of maskless people in 2020.

The next tool for slowing the spread and flattening the curve is to avoid large gatherings. Just as we have seen in headline-grabbing “super spreader” events during 2020, large gatherings can have disproportionate impacts on the transmission of disease by increasing the number of interactions between infected and healthy patients. The deer equivalent of 2020’s choirs or large indoor gatherings are high density populations. Researchers know that higher deer densities facilitate greater transmission and prevalence of CWD. Thus, to manage CWD, landowners, hunters, and others with influence over deer must work to manage populations through hunting to keep densities low.

The final tool for managing disease is to stay home. As with our other interventions with CWD, we are not asking the deer to pick up sourdough baking or buy a coloring book and stick it out in their corner of the woods. Rather the deer-equivalent of staying home focuses on emphasizing the importance of humans not moving deer – dead or alive --  long distances. Imagine a CWD-positive deer being harvested in Allamakee County and brought to Webster County for processing and disposed of in a field there. CWD prions would be in that disposed-of carcass and could be encountered by a healthy deer, introducing the disease to the area for the first time. Thus, hunters should not move deer carcasses away from their place of origin, or when carcasses are moved long distances, they must be disposed of in landfills.  

There are notable differences between Covid-19 and CWD. On key difference is in the speed with which CWD spreads. Recall, last year at this time no American had ever heard the word Covid-19 and only epidemiologists knew or concerned themselves with phrases like “flatten the curve” or “slow the spread”. Today just 12 months later, those refrains are repeated everywhere from corporate boardrooms to children’s playgrounds. CWD in contrast has been known in wild members of the deer family since the 1960s and slowly spread across North America. Thus, CWD seems to be like Covid-19 playing out in slow motion. The risk it poses to wild deer will play out over years and decades, rather than the supercharged pace of our current pandemic.

Slower spread however is no excuse for delay in acting to flatten the CWD curve.  Just like Covid-19, solving CWD comes down to the collective impact of individual decisions. Everyone has an important role to play in ensuring that white-tailed deer populations remain healthy and safe. To do that, we must all help deer by changing our behaviors and ensuring deer maintain physical distance, avoid large gatherings, and stay home. If we do that, we can ensure that this wonderful resource is here for families to safely enjoy for generations to come, far beyond the trending lifespan of #FlattenTheCurve.

To learn more about CWD, visit https://naturalresources.extension.iastate.edu/wildlife/cwd