Evaluation of Winter Ticks (Dermacentor albipictus) Collected from North American Elk (Cervus canadensis) in an Area of Chronic Wasting Disease Endemicity for Evidence of PrP(CWD) Amplification Using Real-Time Quaking-Induced Conversion Assay

Chronic wasting disease (CWD) is a progressive and fatal spongiform encephalopathy of deer and elk species, caused by a misfolded variant of the normal prion protein. Horizontal transmission of the misfolded CWD prion between animals is thought to occur through shedding in saliva and other forms of excreta. The role of blood in CWD transmission is less clear, though infectivity has been demonstrated in various blood fractions. Blood-feeding insects, including ticks, are known vectors for a range of bacterial and viral infections in animals and humans, though to date, there has been no evidence for their involvement in prion disease transmission. In the present study, we evaluated winter ticks (Dermacentor albipictus) collected from 136 North American elk (Cervus canadensis) in an area where CWD is endemic for evidence of CWD prion amplification using the real-time quaking-induced conversion assay (RT-QuIC). Although 30 elk were found to be CWD positive (22%) postmortem, amplifiable prions were found in just a single tick collected from an elk in advanced stages of CWD infection, with some evidence for prions in ticks collected from elk in mid-stage infection. These findings suggest that further investigation of ticks as reservoirs for prion disease may be warranted. IMPORTANCE This study reports the first finding of detectable levels of prions linked to chronic wasting disease in a tick collected from a clinically infected elk. Using the real-time quaking-induced conversion assay (RT-QuIC), “suspect” samples were also identified; these suspect ticks were more likely to have been collected from CWD-positive elk, though suspect amplification was also observed in ticks collected from CWD-negative elk. Observed levels were at the lower end of our detection limits, though our findings suggest that additional research evaluating ticks collected from animals in late-stage disease may be warranted to further evaluate the role of ticks as potential vectors of chronic wasting disease.