Erysipelothrix rhusiopathiae clone reemergence in association with a multi-year mass mortality event in high Arctic muskoxen (Ovibos moschatus).

We investigated a multi-year mass mortality event in muskoxen (Ovibos moschatus) on Ellesmere and Axel Heiberg Islands, Nunavut, Canada and linked the deaths with the "Arctic clone" of the bacterium Erysipelothrix rhusiopathiae (Er), making this the third reported independent mass mortality event in muskoxen associated with this bacterial strain. Between 2021 and 2024, we collected and analyzed samples from 139 unique muskox carcass sites using gross and microscopic pathology, bacterial culture, and molecular methods. Er Arctic clone was found in association with > 70% of sampled carcasses. Our results underscore the geographic expanse over which this unique clonal lineage of Er has now spread, its apparently high virulence in muskoxen, and its ongoing importance as a consideration in conservation and monitoring efforts related to this species.