Published: September 23, 2022
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 reindeer are all known to be naturally infected and currently 29 states, 2 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. This report describes the CWD surveillance program conducted in northeast Washington during Fiscal Year (FY) 2021.
During FY 2021, the Department focused efforts to collect samples from adult (≥1 year old) white-tailed deer in four CSUs in northeast Washington. These four CSUs encompassed seven 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 425 samples during FY 2021 and 423 were suitable for testing. Two samples were the incorrect tissue type, likely salivary gland, and could not be tested for CWD. Chronic wasting disease was not detected in any of the 423 testable samples. Of the testable samples, two were female mule deer, and the remaining 421 samples were white-tailed deer (148 females ranging in age from 0 – 15 years old; 269 males ranging in age from 0 – 19 years old; four unknown sex). Four males and two females were aged in the field as either a yearling or adult but based on cementum annuli analysis were determined to be fawns. The median age of the 184 deer for which cementum annuli analysis results were available at the time of report writing was 3 years old.
While CWD was not detected in any of the testable samples, sample sizes limited the Departments ability to conclude with 95% confidence that CWD was not present at 1% prevalence in any of the CSUs in northeast Washington. However, it is expected that as the surveillance program continues and outreach expands, participation and thus sample collection will increase as more hunters and roadkill salvagers are made aware of CWD and the importance of submitting samples. Also, all samples were submitted voluntarily, and mandatory sample submission may become necessary to achieve sample size goals in the future.