Tularemia From a Harbor Seal: A First Case Linked to a Marine Mammal, Washington, 2023

Summary

• Tularemia is a disease people catch from animals, caused by the bacterium Francisella tularensis, found most often in rabbits, hares and rodents.
• In 2023, a wildlife worker in Washington caught it after a necropsy on a dead harbor seal — the first known human case acquired from a marine mammal, and the first time the bacterium had been found in one.
• People who work with marine wildlife, clinicians and public health investigators should know the risk and follow established safety protocols.

The disease

People can catch tularemia by handling infected animals, from insect bites, by drinking contaminated water or by breathing in the bacteria; its form tends to depend on the route. With antibiotics, most patients recover fully. Washington reports fewer than 10 human cases a year.

The case

On October 3, 2023, a healthy 32-year-old woman from Kitsap County, a wildlife biologist with a nonprofit that examines harbor seals found dead around Puget Sound, nicked a finger with a scalpel — through her glove — while examining a dead harbor seal (Phoca vitulina) from South Puget Sound. She was wearing a surgical gown, goggles, an N-95 respirator and surgical gloves.

• The cut seemed to heal, but about 2 weeks later became inflamed and painful, and she developed fever, swollen lymph nodes on the same side, cough and congestion.
• On October 20, her primary care provider prescribed doxycycline and a topical antibiotic, and she recovered fully. Tularemia wasn't suspected, but fluid from the wound was cultured and flagged as a possible Francisella.
• On November 3, the Washington State Public Health Laboratory confirmed F. tularensis by culture, antibody staining and PCR.

The seal

The seal's necropsy showed signs of infection in its chest and abdominal organs but no significant wounds. Health officials and the Washington Department of Fish and Wildlife sent tissue for testing: six specimens were PCR-positive, and CDC's sequencing of the lung identified F. tularensis type B (subspecies holarctica), similar to strains found before in the western U.S. The patient's own isolate had been destroyed under select-agent rules, so the two couldn't be compared directly.

No other cases: one other volunteer at the necropsy and the lab workers who handled the sample were monitored, and no one else fell ill.

What it means

Most tularemia in the northwestern U.S. comes from the environment or from rodents and rabbits, but marine mammals should now be considered a possible source. People who handle harbor seals — and the clinicians and investigators who see them — should be alert to tularemia and other diseases spread by animals, wear proper protective equipment, and follow safety protocols.

Sources

Based on Wendy Inouye, Hanna N. Oltean, Michelle McMillan and others (Kitsap Public Health District, the Washington State Department of Health and Public Health Laboratory, Washington State University and CDC), "Notes from the Field: Tularemia Associated with Harbor Seal Necropsy — Kitsap County, Washington, October 2023," MMWR, Centers for Disease Control and Prevention; published by CDC and in the public domain; rewritten in hubnx's own words.