Chronic wasting disease is associated with elevated cortisol concentrations in a white‐tailed deer population

Many clinical signs of chronic wasting disease (CWD) in white‐tailed deer Odocoileus virginianus are consistent with those of chronic stress including hyperexcitability, head tremors, teeth grinding, pacing, excessive salivation, drinking, and urination. Deer with CWD‐positive (CWD+) status are more likely to exhibit poor body condition and to die, and clinical signs may be exacerbated by chronic stress. Chronic stress may inhibit the ability to fight secondary infections. Therefore, it is important to evaluate hormones linked to stress, such as cortisol, and their relationship with CWD status. We tested whether cortisol concentrations were associated with CWD status by quantifying cortisol in hair from hunter‐harvested deer. We supplemented this analysis with a small sample size (n = 9) of serum from captured deer where CWD status was known within 30 days of capture due to mortality. Cortisol in hair is representative of long‐term cortisol concentrations. In contrast, serum cortisol represents stress during capture and is highly variable by individual. In hair from hunter‐harvested deer, cortisol concentrations were significantly higher in CWD+ animals (p = 0.033). Cortisol concentrations in the hair of CWD+ deer were 1.3 pg mg −1 hair, (SE = 0.24) and for CWD non‐detect (ND) were 0.79 pg mg −1 , (SE = 0.09). Despite small sample sizes, serum cortisol was still on average higher in CWD+ (X‐= 5.9 μg dl −1 , SE = 1.6) compared to CWD ND deer (X‐= 2.9 μg dl −1 , SE = 1.3), though this relationship was not significant (p = 0.183). Combining these independent tests, there was significant evidence that cortisol concentrations differed between CWD+ and CWD ND animals (Fisher's method: p = 0.031). There is mounting biological evidence that this observed association is directionally causal – CWD likely causes elevated cortisol and not vice versa. These results indicate that chronic stress may facilitate the adverse effects of CWD and make deer more susceptible to other sources of mortality.