Expanding CWD disease surveillance options using environmental contamination at deer signposts

Abstract

Environmental surveillance can allow early detection of diseases, which increases management options and can improve disease trajectories. Chronic wasting disease (CWD) in cervids is a significant prion disease that has been spreading across North America since the 1960s, leading to cervid population declines and concern from hunters and state wildlife agencies. White-tailed deer have a unique breeding season behaviour called scraping, where they deposit urine and saliva at shared sites. Since both these fluids can contain CWD prions, scrape sites have the potential to serve as sentinel sites for environmental surveillance of CWD. To examine this potential, we used camera traps to monitor deer behaviour and collected environmental samples from 105 scrape sites. The 48 km2 study site was located at the centre of the CWD zone in southwestern Tennessee, where CWD prevalence is ~50%. We also sampled scrapes in northern Mississippi at the leading edge of the same CWD distribution to test the potential for early CWD detection using scrape sampling. From camera data, we identified 218 unique bucks visiting 105 scrapes, with a mean of 12.2 ± 7.5 bucks per scrape (mean ± SD, range 1–39) and individual bucks visiting a mean of 5.9 ± 4.6 monitored scrapes each (range 1–23). Using real-time quaking-induced conversion (RT-QuIC), we detected prion seeding activity in 20% of the soil and 41% of the licking branches of the scrape sites within the CWD study area, and in 25% of the soil and 11% of the licking branches of scrape sites sampled at the edge of the known CWD distribution. Our data show there is environmental prion contamination at scrape sites. This supports the idea that scrapes could serve as early warning sentinel sites for CWD surveillance through testing soil and licking branches for prion seeding activity, especially in areas with limited access to harvested deer samples.