Tularemia (Francisella tularensis subsp. holarctica) found in Cook Inlet beluga whales, researchers report

Scientists analyzing stranded Cook Inlet beluga whales reported detection of Francisella tularensis subspecies holarctica (tularemia) in multiple necropsied animals, marking the first known confirmed cases in cetaceans worldwide, presenter Natalie Rouse said. The finding followed agnostic sequencing by the University of Alaska Anchorage Bortz Lab, PCR confirmation at Colorado State University, multilocus sequence typing at CDC, and immunohistochemistry read by an Alaska pathologist.

Rouse, a necropsy biologist with Alaska Veterinary Pathology Services and the University of Alaska Anchorage, said agnostic Oxford Nanopore sequencing identified Francisella in liver and lung tissue from two animals; subsequent PCR and MLST confirmed subspecies holarctica and phylogenetic analysis aligned the beluga sequences with a 2023 Washington state harbor seal sequence. "These are the first cases in any whale at all worldwide that we — that we're aware of," Rouse said.

Cook Inlet belugas form a critically endangered population of roughly 300 animals that reside year-round near Anchorage, Alaska; Rouse described an unusual mortality event in fall 2023 when seven whales were found dead in about 60 days. Gross and histopathology across cases showed pulmonary edema, bronchopneumonia, lymphadenitis and other lesions consistent with a pneumonic form of disease. Retrospective PCR and IHC on archived samples back to 2012 identified Francisella in the 2017 event as well as in the 2023 and early 2024 cases, and the team found no evidence of Francisella in other years tested.

Rouse said the most plausible exposure route for belugas is contaminated water, citing belugas’ known tendency to enter fresh water and the detection of Francisella sequences associated with freshwater-linked strains. She emphasized that humans working with marine mammals should use appropriate PPE; Rouse noted that responders who handled the 2023 cases did not report illness, and that COVID-era mask use and current full PPE practices are important protections.

The investigators published a research letter describing the June 2025 sequencing results, and Rouse said further work will examine environmental drivers of these events as part of her doctoral research. The detection raises questions about environmental sources and timing: investigators are trying to understand why events occurred in 2017 and again in 2023–2024 but were not detected in intervening years.

In Q&A, Rouse said she had notified the state veterinarian and that other wildlife institutions (e.g., Alaska Wildlife Conservation Center) reported no overlapping cases at that time. She urged caution but said there is no evidence yet of broader marine-mammal or human outbreaks linked to these detections.

The webinar hosts said the talk’s slides and a captioned recording will be posted on the ZOHU Call web page and provided contact emails for follow-up questions.