It is reported that a researcher from a Russian plague research institute died from a case that has been identified as plague.

Although there is still much that is unknown about the situation, according to local media reports, as many as 189 people in the Irkutsk region of eastern Siberia, Russia, have been placed under medical observation due to exposure to this potentially fatal disease.

The World Health Organization (WHO) stated that it has taken note of reports that a laboratory worker in Irkutsk Oblast died of severe pneumonia on Friday and has provided support to Russia. In a statement sent to CNBC, the WHO indicated that the cause of death has not yet been officially confirmed, and laboratory tests are still ongoing.

The WHO stated: "All contacts of the patient have been identified and are under disease surveillance. As of now, no one has shown symptoms of the disease."

What is plague, and how does it spread?

Plague is a rare but potentially fatal bacterial infection that remains endemic in certain parts of the world, including some areas of the western United States; if identified early, it can be treated with antibiotics. It is caused by the zoonotic bacterium Yersinia pestis (Yersinia pestis), which is commonly found in small mammals and their fleas, and there are several types of this bacterium.

Bubonic plague is a classic type of plague associated with the Black Death in the 14th century. If left untreated, the bacteria can escape the lymphatic system and enter the bloodstream or lungs, leading to septic plague or pneumonic plague, according to the World Health Organization.

The latest case in Russia appears to be pneumonic plague, which is a bacterial infection of the lungs. It may have developed from other types of plague or could have been contracted by inhaling infectious particles.

Unlike bubonic plague, which usually causes swollen and painful lymph nodes and generally does not spread from person to person, pneumonic plague may be more concerning from the perspective of disease control and prevention.

Yersinia pestis exists in natural animal hosts, especially rodents, which makes eradication extremely difficult. According to the World Health Organization (WHO), animal plague is present on all continents except Oceania, but this does not mean that human cases will occur wherever these hosts are found.

Brendan Lunn, a professor at the London School of Hygiene and Tropical Medicine ( Brendan Wren ), said to CNBC: "These laboratory-acquired cases of pneumonic plague may potentially be transmitted through the respiratory tract." He added, "The bacterium Yersinia pestis... is quite contagious, but not as so as SARS2 / COVID."

What is the current progress of this suspected case in Russia?

According to the Russian public health regulatory agency Rospotrebnadzor, this employee who works at the Irkutsk Institute for Plague Control has been diagnosed with “pneumonia of unknown cause.” In a statement released on Sunday, the agency stated that the situation in Irkutsk and Sherekhov is “stable” and that measures have been taken in response to this case.

The head of the neighboring Republic of Buryatia, Aleksey Zidenov ( Alexei Tsydenov ), stated on social media that the employee died from a type of plague not specified, but denied that he had ever been to Buryatia.

CNBC It is not possible to independently verify these reports. The Russian Ministry of Health did not immediately respond to requests for comments from CNBC.

Lun stated that there are still approximately 2,000 cases of plague each year, and these cases can be treated with standard antibiotics. "However, multi-drug resistant strains are emerging, and if laboratories are studying such strains, then treatment options may be limited," he added.

Lun pointed out that laboratory staff may be working with samples of the plague bacterium Yersinia pestis in order to improve vaccines for areas affected by endemic plague; he added, 'If Yersinia pestis were to be weaponized, then it might be necessary to prepare vaccines for military personnel.'

Rospotrebnadzor indicates that no microorganisms related to the patient's occupational activities were detected. The institution did not respond immediately to CNBC further requests for comment.

The WHO has informed CNBC that, based on the currently available unofficial information, the public health risk to the general population seems to be low. The risk assessment will be updated once more information becomes available.

— CNBC's Jenny Lee has contributed to this report.