According to reports, a researcher at Russia’s Institute for Plague Control has died from symptoms confirmed to be plague infection.
Much is still unclear about the progress, but local media reports say as many as 189 people are under medical observation in the Irkutsk region of eastern Siberia after being exposed to the potentially deadly disease.
The World Health Organization said it was aware of reports that a laboratory worker in the Irkutsk region died of severe pneumonia on October 2, 2026, and has offered assistance to Russia. The cause of death has not been officially confirmed and it is understood that clinical tests are ongoing, authorities told CNBC in a statement.
“All contacts of the patient have reportedly been identified and are being monitored for the disease, but none have shown symptoms of the disease to date,” the WHO said.
What is the plague and how does it spread?
Plague is a rare but potentially fatal bacterial infection that remains endemic in parts of the world, including the western United States, but can be treated with antibiotics if quickly identified. The disease is caused by the zoonotic bacterium Yersinia pestis, which is usually found in small mammals and their fleas, and comes in many forms.
The bubonic plague is a classic plague associated with the Black Death of the 14th century. Without treatment, the bacteria can escape the lymphatic system and enter the bloodstream and lungs, causing sepsis and pneumonic plague, according to the World Health Organization.
The latest cases in Russia appear to be pneumonic plague, where the bacteria infects the lungs. It can be contracted from other forms of plague or by inhaling infectious particles.
In contrast to bubonic plague, which causes swollen and painful lymph nodes (buboes) and is generally not transmitted from person to person, pneumonic plague may be of greater concern from a disease management perspective.
Yersinia pestis is very difficult to eradicate because of its natural animal reservoir, especially rodents. The WHO states that animal epidemics exist on all continents except Oceania, but that does not mean human cases will occur everywhere those sources exist.
“This laboratory-acquired case of pneumonic plague could be transmitted by the respiratory route,” Professor Brendan Wren of the London School of Hygiene and Tropical Medicine told CNBC. “The plague bacterium…is quite contagious, but not as contagious as SARS2/COVID-19.”
What’s going on with the suspicious incidents in Russia?
Russia’s public health watchdog Rospotrebnadzor said the worker at the Institute for Plague Control in Irkutsk was diagnosed with “pneumonia of unknown cause.” The authorities said in a statement on Sunday that the situation in the cities of Irkutsk and Sherekhov was “stable” and that measures were being taken in response to the incident.
Alexei Tsydenov, head of the neighboring Republic of Buryatia, where the employee reportedly traveled in recent days, said on social media that the employee died of an unspecified type of plague, but denied traveling to Buryatia.
CNBC has not been able to independently verify the report. Russia’s Ministry of Health did not immediately respond to CNBC’s request for comment.
Wren said there are still about 2,000 cases of plague each year that can be treated with standard antibiotics. “However, multi-antibiotic-resistant strains are emerging, and treatment options may be limited if laboratories are studying such strains,” he added.
Dr. Wren noted that laboratory staff may have been working with Y. pestis samples to produce improved vaccines for areas of the world where the bacterium is endemic, adding: “If Y. pestis was weaponized, a military-grade vaccine might be desirable.”
Rospotrebnadzor said that no microorganisms associated with the occupational activities of patients with the disease have been detected. The agency did not immediately respond to CNBC’s request for further information.
The WHO told CNBC that based on available unofficial information, the public health risk to the general population appears to be low and that it will update the risk assessment as more information becomes available.
—CNBC’s Jenny Lee contributed to this report
