Management of chronic wasting disease in ranched elk: conclusions from a longitudinal three-year study

Abstract

Chronic wasting disease is a fatal, horizontally transmissible prion disease of cervid species that has been reported in free-ranging and farmed animals in North America, Scandinavia, and Korea. Like other prion diseases, CWD susceptibility is partly dependent on the sequence of the prion protein encoded by the host's PRNP gene; it is unknown if variations in PRNP have any meaningful effects on other aspects of health. Conventional diagnosis of CWD relies on ELISA or IHC testing of samples collected post-mortem, with recent efforts focused on antemortem testing approaches. We report on the conclusions of a study evaluating the role of antemortem testing of rectal biopsies collected from over 570 elk in a privately managed herd, and the results of both an amplification assay (RT-QuIC) and conventional IHC among animals with a several PRNP genotypes. Links between PRNP genotype and potential markers of evolutionary fitness, including pregnancy rates, body condition, and annual return rates were also examined. We found that the RT-QuIC assay identified significantly more CWD positive animals than conventional IHC across the course of the study, and was less affected by factors known to influence IHC sensitivityincluding follicle count and PRNP genotype. We also found that several evolutionary markers of fitness were not adversely correlated with specific PRNP genotypes. While the financial burden of the disease in this herd was ultimately unsustainable for the herd owners, our scientific findings and the hurdles encountered will assist future CWD management strategies in both wild and farmed elk and deer.

Cross-validation of the RT-QuIC assay for the antemortem detection of chronic wasting disease in elk

“…A total of 702 samples were collected and analysed, with 387 collected in the first year and 315 collected in year two. A lengthy description of sampling techniques and handling procedures are described elsewhere [43]. In the spring of 2017 (15 months after initial collection of year one biopsies and 3 months after collection of year two biopsies), frozen sample homogenates were distributed to several CWDfocused laboratories across the United States and Canada with an expressed interest in cross validating the original results (Laboratories B through E).…”

“…These samples may additionally be positive independent of specific markers (e.g. follicle count or PRNP genotype) which may affect conventional diagnosis [14,18,43]. Importantly, amplification assays, like ELISA, can be streamlined and scaled to allow for rapid and automated testing of large numbers of samples, with real-time readouts independent of the need for specialized pathology training.…”

“…This manuscript presents a cross-validational study of the application of RT-QuIC testing to recto-anal mucosa associated lymphoid tissue (RAMALT) biopsies collected antemortem from 471 individual Rocky Mountain elk (Cervus elaphus canadensis) in a controlled area, with endemic CWD approaching 33% prevalence over the course of a two-year study [14,43]. Testing by RT-QuIC was performed by five different laboratories across the United States and Canada, with results compared between laboratories and to IHC of RAMALT, as well as conventional postmortem testing of the brainstem and retropharyngeal lymph nodes by IHC, when available.…”

“…Testing by RT-QuIC was performed by five different laboratories across the United States and Canada, with results compared between laboratories and to IHC of RAMALT, as well as conventional postmortem testing of the brainstem and retropharyngeal lymph nodes by IHC, when available. The samples were initially tested by RT-QuIC, blindly, at the primary laboratory ('Laboratory A') as part of a larger study, with IHC also performed blindly and concurrently by a national regulatory laboratory; aspects of this study are reported elsewhere [14,43]. Samples were subsequently distributed to and assayed concurrently by the four remaining laboratories ('Laboratories B through E') at times ranging between 3 and 15 months postcollection.…”

Estimating relative CWD susceptibility and disease progression in farmed white-tailed deer with rare PRNP alleles

“…[45,54] Elk heterozygous or homozygous for the 132L polymorphism likewise show reduced susceptibility in both wild and captive populations, however 132LL homozygous elk have only rarely been found to be infected. [48,55] In the present study, we sought to better define the relative susceptibilities of whitetailed deer heterozygous and homozygous for several different PRNP alleles, including 95H, 96G and 96S, 116G, and 226K. Samples were analyzed from nearly 2100 farmed deer depopulated following exposure to CWD, including 714 deer infected with CWD, with postmortem prevalence ranging from 6-83% across 20 separate herds in the United States and Canada.…”