A laboratory technician who worked at a research institution in Russia studying the plague bacterium has died, and the cause of death has not yet been determined. This incident has raised doubts among experts in infectious diseases, who say that the circumstances surrounding this case are unusual, and that key details remain unanswered.

According to local reports, about 200 people in the Irkutsk region of Siberia have been placed under medical observation or isolated. Other reports indicate that an accident related to bacteria occurred at the laboratory involved before the death of this person. CNBC is unable to independently verify these reports.

Although global health agencies indicate that the risk of a larger-scale outbreak seems low, experts told CNBC that the reported deaths are difficult to reconcile with the strict protective measures typically adopted when dealing with such deadly pathogens.

The head of the Yersinia research group at the Pasteur Institute in Paris, Javier Pizarro - Cerda, told CNBC that he was "very surprised" by the reports coming from Russia, as those engaged in plague research usually take strict protective measures to avoid exposure risks.

He said, "You will be wearing a full set of protective gear, a mask, and gloves. So even if you break the test tube, you should still be protected." He added that in Russia, there is still a vaccine available for plague. However, Pizarro-Cerda indicates that this vaccine does not meet the standards expected in other places; its protective effect is weaker and lasts for a shorter duration.

A fatal disease

Plague is a often fatal disease that progresses very rapidly. Without treatment, the fatality rate of pneumonic plague is nearly 100%; even with treatment, the fatality rate is about 50%.

Experts in the bacterium Yersinia pestis, which causes plague, told CNBC that isolating and monitoring anyone who has had contact with patients is a normal and reasonable approach.

As for the origin of this suspected case of pneumonic plague, Pizarro-Cerda stated that the plague bacterium Yersinia pestis naturally exists in animal hosts, especially rodents, but it is highly unlikely that this employee contracted the infection elsewhere.

He said that this person must have been to a very specific place, or come into contact with contaminated individuals, or have been exposed to sick animals in the wild environment.

The host distribution of Yersinia pestis, the bacterium that causes plague, covers every continent except Oceania, but this does not mean that human cases will occur in all places where hosts exist.

The Russian public health regulatory agency Rospotrebnadzor stated that the situation is under control and that measures have been taken to address it. The agency also noted, "Based on extensive testing, no microorganisms related to the patients' occupational activities were found in their samples."

The World Health Organization ( WHO ) stated in a declaration to CNBC that the cause of death has not yet been confirmed, and tests are reportedly underway. WHO added that all contacts of the patient are said to have been identified and are under disease surveillance, and so far no one has shown symptoms.

There are still key issues that remain unresolved.

If there is no suspicion of exposure to plague, it is still unclear why dozens of people in that area have been placed under medical observation.

Pizarro-Cerda indicates that plague detection is simple and quick. “If an autopsy is performed, it should be very easy, because if it’s pneumonic plague, the patient’s lungs would be filled with bacteria,” he said. Considering that the death occurred on October 2nd, if tests have been conducted, authorities should now be able to find evidence of the presence of plague.

The Russian Ministry of Health and the Russian Public Health Regulatory Agency Rospotrebnadzor have not responded to requests for further information from CNBC.

A spokesperson for the European Centre for Disease Prevention and Control stated that they are aware of a case of pneumonia of unknown cause in eastern Russia, which is suspected to be related to plague, but reminded that "this suspicion has not yet been confirmed."

"The case is located in Irkutsk, Siberia, near the border between Russia and Mongolia. There is very little travel between Irkutsk and the EU/European Economic Area, especially at a time when Russia has launched a war against Ukraine," the spokesperson added.

According to the information currently available, there have been no reports of additional cases, nor is there any ongoing person-to-person transmission.

Unlike the more well-known plague that affected the lymphatic system and was associated with the Black Death in the 14th century, pneumonic plague can spread from person to person. Although its transmissibility is not as high as that of influenza or the COVID-19 virus, it still deserves more attention from the perspective of disease outbreaks.

Professor Brendan Wren from the London School of Hygiene and Tropical Medicine told CNBC that plague is still endemic in many regions of the world, including parts of the western United States, but "people should not worry too much, as the transmission of the plague bacterium between people is usually weak."

However, Associate Professor of Cellular Microbiology at the University of Reading, Simon Clarke, told CNBC, "Even so, any case is concerning, especially in this situation."

He said that in order for scientists to accurately assess the situation, what is most needed now is to "make public what this patient was doing at the time, why they did it, what caused their death, as well as what they did and where they did it, in order to try to establish a firewall for those who came into contact with them."

The U.S. State Department stated that it is closely monitoring the situation with the U.S. Centers for Disease Control and Prevention, but emphasized that many details have not yet been confirmed. “We encourage Russian authorities to share accurate information promptly and openly,” a spokesperson told CNBC.

U.S. President Donald Trump told reporters on Monday that the United States will do its utmost to help Russia.

Macro Advisory CEO Chris Weafer stated that in the past five to six weeks, the working relationship between Moscow and Washington seems to have improved, and there has been a lot of interaction among officials at different levels.

On Tuesday, in the program “Squawk Box Europe” on CNBC, Weafer stated: “In this sense, Trump’s offer of help did not surprise me. Part of the reason is to ensure that this does not evolve into another major international incident that results in deaths and disrupts the global economy.”

But this also reflects that there is currently a continuous and seemingly quite stable dialogue between Washington and Moscow on multiple issues, one of the most important of which is, of course, the Ukraine-Russia conflict.