Detection of two dissimilar Chronic Wasting Disease isolates in two captive Rocky Mountain elk (Cervus canadensis) herds

Authors: NICHOLS, TRACY - Animal And Plant Health Inspection Service (APHIS); Nicholson, Eric; LIU, YIHIU - Case Western Reserve University (CWRU); SPRAKER, TERRY - Colorado State University; WOOD, MARY - Wyoming Department Of Game & Fish; LAVELLE, MICHAEL - Colorado State University; FISCHER, JUSTIN - Colorado State University; KONG, QINGZHONG - Case Western Reserve University (CWRU); VERCAUTEREN, KURT - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Prion
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2021
Publication Date: 12/16/2021
Citation: Nichols, T.A., Nicholson, E.M., Liu, Y., Spraker, T.R., Wood, M., Lavelle, M., Fischer, J., Kong, Q., Vercauteren, K.C. 2021. Detection of two dissimilar Chronic Wasting Disease isolates in two captive Rocky Mountain elk (Cervus canadensis) herds. Prion. 15(1):207-215. https://doi.org/10.1080/19336896.2021.1982333.
DOI: https://doi.org/10.1080/19336896.2021.1982333

Interpretive Summary: Chronic wasting disease (CWD) continues to spread in both wild and captive cervid herds in the United States and Canada, and has now been identified in wild reindeer and moose in Norway and Finland. Although the disease has been studied for years, there is still much unknown about CWD. In particular, there is a lack of comprehensive knowledge about the variety and characteristics of isolates or strains of CWD that exist on the landscape. Multiple strains of scrapie in sheep have been identified and more than one strain of CWD appears to be present in cervids, but the implications of this on wild and captive cervid herds is unknown. In this study, samples were evaluated from two captive elk populations with differing history and timelines of CWD. One had a 16 year history of CWD with consistently low prevalence between 5 and 10%. Twelve of fourteen naïve animals placed on the site remained negative after 5 years of residence. The other location had a nearly 40-year known history of CWD with long-term environmental accrual of prion leading to nearly 100% of naïve animals developing clinical CWD within two to twelve years. This study assess the pathologic and molecular features of the CWD samples from these 2 different geographic locations, and supports that that the 2 sites indeed have different isolates with different attack rates likely as a result of differing molecular properties consistent with there being 2 strains of CWD.

Technical Abstract: Chronic wasting disease (CWD) continues to spread in both wild and captive cervid herds in the United States and Canada, and has now been identified in wild reindeer and moose in Norway and Finland. Although the disease has been studied for years, there is still much unknown about CWD. In particular, there is a lack of comprehensive knowledge about the variety and characteristics of isolates or strains of CWD that exist on the landscape. Multiple strains of scrapie in sheep have been identified and more than one strain of CWD appears to be present in cervids, but the implications of this on wild and captive cervid herds is unknown. In this study, samples were evaluated from two captive elk populations with differing history and timelines of CWD. One had a 16 year history of CWD with consistently low prevalence between 5 and 10%. Twelve of fourteen naïve animals placed on the site remained negative after 5 years of residence. The other location had a nearly 40-year known history of CWD with long-term environmental accrual of prion leading to nearly 100% of naïve animals developing clinical CWD within two to twelve years. Obex samples of several elk from the two sites were compared for CWD prion staining, genotypes at prion protein (PrP) gene codon 132, and conformational stability of CWD prions. CWD prions in the obex from site 2 had a lower conformational stability and slightly different amount of prion staining than those from site 1. However, Western blot analysis using three different antibodies failed to reveal significant differences in band pattern or sizes of the protease-resistant prion protein between the two sites. These findings were independent of PrP genotype at codon 132, suggesting the existence of different CWD isolates between the two sites. Further work needs to be done to further elucidate the differences between these two isolates under well controlled experimental conditions.