Washington Department of Fish and Wildlife’s Chronic Wasting Disease Surveillance Program Annual Report: July 2023 – June 2024

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 34 states, four 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. The first detection of CWD in the state of Washington was confirmed in July 2024. The sample was submitted to Washington Disease Diagnostic Laboratory (WADDL) with a batch of other samples collected between February and June of 2024.

In 2021, as CWD detections moved closer to Washington each year, the Washington State Legislature prioritized CWD surveillance by providing the Department budget proviso funds 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”). In January of 2024, the Province of British Columbia confirmed two positive cases of CWD in the Kootenay region in the eastern portion of the state. The first came from a hunter harvested mule deer buck and the second from a road-killed white-tailed doe sampled as part of their CWD surveillance program. This makes British Columbia the fourth province with CWD positive deer found in their wild populations, and the second time CWD has been detected in a bordering jurisdiction to Washington. This report describes the CWD surveillance program conducted in Region 1 during Surveillance Year (SY) 2023 (July 1, 2023- June 30, 2024).

During SY23, 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% con􀏐idence 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 796 samples during SY23 and 766 were suitable for testing. Thirty samples were either the incorrect tissue type, likely salivary gland, abscessed, too decomposed, or an inadequate amount of tissue was collected and could not be tested for CWD. Chronic wasting disease prions were detected in one of the testable samples. Of the testable samples, 413 were from white-tailed deer (348 male, 130 female), 280 mule deer (207 male, 73 female), 36 Rocky Mountain elk (9 male, 27 female) and one female moose that was part of a research study. Five samples collected were submitted for testing based on suspicious clinical signs and CWD was not detected (one sample was not testable; however, this animal was a fawn and likelihood of clinical CWD is low for this age-class).

The first detection of CWD in the state of Washington was confirmed in July 2024 in CSU W47. The pre-detection surveillance plan helped the Department detect this case of CWD, however, sample sizes continue to limit 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. The detection was known after the surveillance year ended; therefore, details of the response actions are unknown at the time of report writing. The Department will reference the actions outlined in the Washington State Chronic Wasting Disease (CWD) Management Plan to guide the initial emergency response and subsequent actions.