Ecology and chronic wasting disease epidemiology shape prion protein gene variation in Rocky Mountain elk (Cervus elaphus nelsoni)

Authors: HOAR, BRUCE - University Of Wyoming; ERNEST, HOLLY - University Of Wyoming; JOHNSON, LAURA - Wyoming Department Of Game & Fish; LACAVA, MELANIE - University Of California, Davis; SANDIDGE, DOUGLAS - University Of Wyoming; GEROW, KEN - University Of Wyoming; Mousel, Michelle; GALLOWAY, NATHAN - National Park Service; SWAIN, WILLIAM - University Of California, Davis; MALMBERG, JENNIFER - University Of Wyoming

Submitted to: Journal of Wildlife Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2023
Publication Date: 1/30/2024
Citation: Hoar, B.R., Ernest, H.B., Johnson, L.N., LaCava, M.E., Sandidge, D.J., Gerow, K., Mousel, M.R., Galloway, N.L., Swain, W., Malmberg, J.L. 2024. Ecology and chronic wasting disease epidemiology shape prion protein gene variation in Rocky Mountain elk (Cervus elaphus nelsoni). Journal of Wildlife Diseases. 60(2):496-501. https://doi.org/10.7589/JWD-D-23-00062.
DOI: https://doi.org/10.7589/JWD-D-23-00062

Interpretive Summary: Chronic Wasting Disease (CWD) is a fatal neurological disease of cervids that is spreading across the US landscape. There is an increased in the prevalence of the prion gene codon 132 leucine (L) amino acid in Rocky Mountain elk within states endemic for CWD. However, within a state, fine scale landscape evaluation of prion 132 alleles has not been studied. Prevalence of CWD in Wyoming varied from 0.2 to 8.1% from 2011 to 2018 when 1,060 elk from 14 herd units were sampled. There was a 9.6% increase in the odds an elk would have an L allele with each 1% increase in CWD prevalence in the herd unit. This study confirms that the prevalence of CWD is influencing the genetics of Rocky Mountain elk. The longer-term impact of disease-driven adaptation is an important consideration for CWD management. The potential for L allele fixation at prion codon 132 in CWD endemic regions is unclear, meriting studies to assess fitness trade-offs and balancing selection in elk populations with CWD. In addition, evaluation of prion shedding during the elongated incubation period of codon 132 L elk needs to be conducted to ascertain environmental prion contamination from these genetically adapted animals.

Technical Abstract: As chronic wasting disease (CWD) continues to spread across North America, the relationship between CWD and host genetics has become of interest. In Rocky Mountain elk (Cervus elaphus nelsoni), one or two copies of a leucine allele at codon 132 of the prion protein gene (132L*) has been shown to prolong the incubation period of CWD. Our study examined the relationship between CWD epidemiology and codon 132 evolution in elk from Wyoming, USA from 2011 to 2018. Using PCR and Sanger sequencing, we genotyped 997 elk and assessed the relationship between genotype and CWD prevalence estimated from surveillance data. Using logistic regression, we showed that each 1% increase in CWD prevalence is associated with a 9.6% increase in the odds that an elk would have at least one copy of leucine at codon 132. In some regions, however, 132L* variants were found in the absence of CWD, indicating that evolutionary and epidemiologic patterns can be heterogeneous across space and time. We also provide evidence that naturally occurring CWD is not rare in 132L* elk, which merits the study of shedding kinetics in 132L* elk and the influence of genotype on CWD strain diversity. The management implications of cervid adaptations to CWD are difficult to predict. Studies that investigate the degree to which evolutionary outcomes are shaped by host spatial structure can provide useful epidemiologic insight, which can in turn aid management by informing scale and extent of mitigation actions.