Erysipelothrix in Cook Inlet, Alaska, USA: an emerging bacterial pathogen of the endangered Cook Inlet beluga whale.

Erysipelothrix is a genus of opportunistic bacteria of humans and animals. In 2019, a marked increase in infections by the zoonotic bacterium Erysipelothrix in Cook Inlet (Alaska, USA) beluga whales Delphinapterus leucas (CIBs) was detected through routine surveillance. A retrospective study was performed using archival records from 1998 to the present; archived samples from 2006 to the present; colleague interviews; and a literature review. Erysipelothrix was detected in 18 of 63 (28.6%) CIBs necropsied between 2006 and 2023, and when present after 2017, it was the primary cause of death. Erysipelothrix was rarely detected in other species of wildlife, domestic animals or in the environment in and around Cook Inlet during the same period. Sequencing of isolates demonstrated several different lineages, negating the possibility of infection from a common source or single strain. The lack of documented previous occurrence of Erysipelothrix in or near Cook Inlet indicates that this is likely an emerging phenomenon.