Global concern is mounting over the death of a 28-year-old female worker at the Anti-Plague Research Institute of Siberia and the Far East in Shelekhov, Irkutsk, Russia, amid conflicting accounts over the cause of her death.

Russia’s infectious disease agency, Rospotrebnadzor, said the woman was diagnosed with “pneumonia of unknown origin,” while reports in Russian media identified her as Daria Shipilova and claimed that she died from pneumonic plague after reportedly dropping a test tube containing live samples of *Yersinia pestis*, the bacterium that causes plague.

According to the reports, Shipilova was taken to hospital on September 29 and died two days later. Nearly 200 people who may have had contact with her are reportedly being monitored for possible signs of infection.

The reports have raised concerns among experts, some of whom warned that the lack of publicly available information bore similarities to the early stages of the COVID-19 pandemic, when uncertainty and limited information fuelled international concern.

The development has also drawn the attention of United States authorities, with the White House and the United States Centers for Disease Control and Prevention reportedly monitoring the situation. U.S. and European officials have also raised concerns over Russia’s history of limited transparency regarding its biosecurity and biological defence programmes, prompting calls for greater openness and data sharing.

However, Russian authorities have maintained that there was no evidence linking the woman’s death to her professional activities. On Monday, Irkutsk Regional Governor Igor Kobzev said a special Rospotrebnadzor expert commission had inspected the region and determined that “the cause of death was pneumonia of undetermined aetiology.”

Kobzev also said the health watchdog found that “no microorganisms linked to the young woman’s professional work were found in her biological samples.”

He added that there had been “no new cases of staff from the anti-plague institute seeking medical attention” since the woman’s death.

The conflicting accounts have heightened attention because of the nature of the institute’s work and the pathogen reportedly involved.

Plague is an infectious disease caused by *Yersinia pestis*, a zoonotic bacterium that is usually found in small mammals and their fleas.

According to the World Health Organisation (WHO), humans can become infected through the bite of infected fleas, direct contact with infectious bodily fluids or contaminated materials, and inhalation of respiratory particles from a person with pneumonic plague.

The WHO said people infected with *Y. pestis* often develop symptoms after an incubation period of one to seven days. It identified bubonic plague as the most common clinical form, characterised by painful swollen lymph nodes known as buboes, while septicaemic and pneumonic plague are less common but severe forms of the disease.

Pneumonic plague is of particular concern because it can be transmitted through respiratory particles from an infected person, unlike bubonic plague, which is commonly associated with transmission through infected flea bites.

The WHO said plague can be a very severe disease, with a case-fatality ratio of 30 to 60 per cent for bubonic plague, while untreated pneumonic and septicaemic plague can be fatal. It, however, noted that antibiotic treatment is effective against the bacteria and that early diagnosis and treatment can save lives.

Human plague remains endemic in several countries, with the WHO reporting that most cases recorded between 2019 and 2025 occurred in the Democratic Republic of the Congo and Madagascar.

Amid the concerns surrounding the reported Russian case, WHO Director-General, Tedros Ghebreyesus, yesterday in a post on X saidp that the WHO and the European Centre for Disease Prevention and Control had assessed the international threat risk as “very low.”

He also noted that there was currently no evidence of sustained human-to-human transmission.

The assessment has helped to temper concerns about a wider international threat, even as authorities continue to monitor the situation and questions remain over the circumstances surrounding the Russian woman’s death.