Alexei Tsydenov, head of the neighbouring Republic of Buryatia, said the woman who reportedly died of plague in the Irkutsk region had not travelled to Buryatia.

“There are no plague outbreaks in the republic, including in the areas bordering Mongolia. The source of infection stems from circumstances unrelated to Buryatia,” he said in a statement.

According to The Moscow Times, the deceased woman was identified as Daria Sh, who worked at the Irkutsk anti-plague institute.

The woman reportedly told medical staff that she had accidentally broken a test tube containing live bacteria while collecting samples for testing.

She was hospitalised in the city of Shelekhov after developing symptoms of severe pneumonia and reportedly died on Thursday.

The Shelekhov district hospital was placed under quarantine while a special commission assessed the situation, The Moscow Times reported.

Around 200 people who had contact with the woman have reportedly been placed under medical isolation and are being monitored for possible symptoms.

Authorities also cancelled planned public events in Irkutsk, while law enforcement agencies reportedly opened a criminal investigation into possible violations of health and safety regulations that may have resulted in a death.

Irkutsk Region Governor Igor Kobzev urged residents to remain calm.

“All identified contact persons have been placed under medical observation. As of today, the contacts show no signs of illness, and their laboratory test results are negative,” Kobzev wrote on Telegram, according to The Moscow Times.

What is pneumonic plague?

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

According to the World Health Organization (WHO), people infected with Y. pestis generally develop symptoms within one to seven days, although the incubation period can vary depending on the form of the disease.

Pneumonic plague is a severe form of plague that affects the lungs and can spread from person to person through respiratory droplets.

Plague can be a very serious disease if left untreated. The WHO says the case-fatality ratio for bubonic plague can range from 30% to 60%, while pneumonic and septicaemic plague can be fatal if not treated promptly.

Early diagnosis and appropriate antibiotic treatment are critical to improving survival.