Published: October 9, 2023
Author(s): Melia T. DeVivo
Chronic wasting disease (CWD) is a fatal neurologic illness of cervids (members of the deer family Cervidae) caused by a prion protein. Free-ranging moose, elk, mule deer, white-tailed deer, and caribou are all known to be naturally infected and currently 31 states, 3 Canadian provinces, Norway, Finland, and Sweden have documented CWD in their wild cervid populations. In Washington, the Washington Department of Fish and Wildlife (hereafter “the Department”) used federal funds to test 6,133 cervids statewide from 2001-2011. After federal funding was no longer available, the Department tested only animals suspected of CWD based on non-specific clinical signs from 2012-2020. Currently, CWD has not been detected in Washington.
With CWD detections closer to Washington each year, the Washington State Legislature prioritized CWD surveillance by providing the Department budget proviso funds in 2021 to expand efforts and begin systematic surveillance. At that time, the closest detection to Washington was in Libby, Montana, thus the Department prioritized the four most northeastern CWD Surveillance Units (CSUs) described in the CWD Management Plan. During the 2021-2022 hunting season, Idaho Department of Fish and Game detected CWD for the first time in two mule deer near the Slate Creek drainage near Lucile. This was the first time CWD was detected in a bordering jurisdiction to Washington, and in response, the Department expanded surveillance throughout the eastern region (hereafter “Region 1”). This report describes the CWD surveillance program conducted in Region 1 during Surveillance Year (SY) 2022 (July 1, 2022- June 30, 2023).
During SY22, the Department focused efforts to collect samples from adult (≥1 year old) white-tailed deer, mule deer, and elk in 11 CSUs in Region 1. These 11 CSUs encompassed 27 Game Management Units (GMUs) that were combined to achieve sampling units of approximately 15,000 deer per CSU. This estimate of deer per CSU is based on harvest within administrative units and is not an estimate of biological population size. Our goal was to sample 300 deer in each CSU to achieve 95% confidence of detecting CWD at 1% prevalence (i.e., the percentage of the population that was affected by CWD during the time samples were collected).
The Department collected 664 samples during SY22 and 654 were suitable for testing. Ten samples were either the incorrect tissue type, likely salivary gland, or an inadequate amount of tissue was collected and could not be tested for CWD. Chronic wasting disease prions were not detected in any of the 654 testable samples. Of the testable samples, 437 were from white-tailed deer (261 male, 173 female, 3 undocumented sex), 189 mule deer (124 male, 65 female), 35 Rocky Mountain elk (7 male, 28 female), 2 moose (1 male, 1 female), and 1 Columbian white-tailed deer (1 male). The Columbian white-tailed deer was collected by the U.S. Fish and Wildlife Service near the Julia Butler Hansen Refuge in Wahkiakum County and submitted as an opportunistic road-kill sample. Two elk outside of the surveillance area were submitted for testing based on suspicious clinical signs and CWD was not detected in either animal.
For the second consecutive year of systematic surveillance since implementing WDFW’s CWD Management Plan, CWD was not detected in any of the testable samples; however, sample sizes limited the Department’s ability to conclude with 95% confidence that CWD was not present at 1% prevalence in any of the CSUs in Region 1. During the surveillance year, all samples were submitted voluntarily. While the Department will continue to explore additional options to incentivize sample submission, mandatory sample submission may become necessary to achieve sample size goals in the future.