A suspected pneumonic plague case in Russia has raised concerns after a 28-year-old woman who worked at an anti-plague laboratory died from pneumonia of undetermined origin.

Russian media identified the woman as Darya Shipilova, an employee at the Irkutsk Anti-Plague Institute of Siberia and the Far East. Russian officials have not confirmed plague as the cause of her death. They have also not linked her illness to her work at the laboratory.

Reports say a second laboratory employee developed pneumonia of undetermined cause. However, the World Health Organization (WHO) said authorities have not yet verified that case.

WHO officials said they were told that the area had no registered plague cases. They also said tests had not detected any high-threat pathogens. The WHO continues to seek information from Russia about laboratory tests and their results.

Nearly 200 people who had contact with the woman have entered precautionary medical observation. Russian health authorities said monitoring of more than 90% of her contacts found no health issues linked to infectious disease. Tests also found no dangerous pathogenic microorganisms.

The suspected case has drawn attention because the woman worked at a facility that studies plague. Plague comes from the Yersinia pestis bacterium and has three main forms: bubonic, pneumonic and septicemic plague.

Pneumonic plague affects the lungs and can spread through respiratory droplets during close contact. Health experts say it remains rare but can become severe quickly. Symptoms may include coughing, difficulty breathing and blood in the phlegm.

Doctors can treat plague with antibiotics, especially when patients receive treatment early. Experts cited in the report said there is currently no evidence that the suspected case poses a wider international threat.

The U.S. Centers for Disease Control and Prevention (CDC) said it is monitoring reports of the suspected case. The agency said the circumstances remain unconfirmed and that there is currently no indication of a broader threat to the United States.

The investigation remains ongoing. Authorities still need to determine whether the woman had plague and, if so, how she became infected.