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Predators & Disease Spread

With the continued spread of Chronic Wasting Disease (CWD), the hypothesis that wolves could be the “best defense” or “first responders” against further spread has been getting increased airtime. But here’s the deal: just as wolves may reduce CWD spread, wolves may not reduce CWD spread. The impact of wolves on CWD dynamics is little more than speculation at this point. Even if research supports one finding in a certain location, that may not apply to another location because there are multitudes of factors that come into play.

Predators are only one factor involved in disease dynamics, especially since “Under some conditions the CWD agent persists in the environment for years in residues from excrement and infected carcasses.”

Research on mountain lion predation on a Colorado deer population infected with CWD found: “Remarkably high infection rates sustained in the face of intense predation show that even seemingly complete ecosystems may offer little resistance to the spread and persistence of contagious prion diseases.”

Research has also demonstrated that CWD prions remain infectious after passage through the digestive system of coyotes, and that “mammalian scavengers could contribute to the translocation and contamination of CWD in the environment.”

Thus, just as it’s reasonable to assume that wolves may play a significant role in disease transmission, it’s also reasonable to assume that wolves may not play a significant role in disease transmission. Another paper, Predation Can Increase the Prevalence of Infectious Disease, makes this important point: “Our results show that there is no complete generalization possible about how shifts in predation pressure translate into shifts in infection levels, without some understanding of host population regulation and the role of acquired immunity.”

What we do know is that there have been decades of research on another disease – brucellosis – in the Greater Yellowstone Ecosystem, as well as research on wolves in the same ecosystem.

Wolves can change the movement patterns of elk. If brucellosis-infected elk disperse into neighboring cattle herds, the elk could transmit the disease to cattle. If brucellosis-infected elk disperse into neighboring elk herds, the elk could further transmit the disease to herds that previously were not infected. This paper proposes that scavengers “likely function as a biological control agent” of brucellosis, but that has yet to be documented.

While there is plenty of speculation on the impact predators such as wolves may have in controlling CWD, no one can say conclusively one way or the other.

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