Plague, an infectious disease caused by the bacterium Yersinia pestis, is primarily transmitted by rodents and their fleas to humans. It is most famously associated with the Black Death pandemic of the 14th century, which killed nearly 200 million people worldwide. Although the disease has not disappeared, cases are recorded annually in certain regions. According to the World Health Organization (WHO), most human cases since the 1990s have been reported in Africa, particularly in Madagascar and the Democratic Republic of the Congo, with nearly 50,000 cases recorded between 1990 and 2020. In 2025, cases were recorded in the United States, but did not lead to an epidemic. The three most common forms of plague are bubonic, septicemic, and pneumonic. All are caused by the same bacterium, but differ in how the infection enters the human body. Pneumonic plague, in particular, can be transmitted rapidly from human to human through droplets containing the bacterium. According to Richard Martinello, an infectious disease specialist at Yale School of Medicine, antibiotics must be administered as soon as the first signs of infection appear to be effective. The WHO warns that if pneumonic plague is not diagnosed and treated early, it can be fatal. Gregory Koblentz, a researcher in biological risk management and a specialist in laboratory security at George-Mason University, noted in Nature that some are wondering if the recent situation in Russia could be the beginning of a "Covid-26" following the 2019 Covid-19 pandemic. He refers to information, denied by Russian authorities, suggesting that the death of Daria Chipilova, an employee of the Siberian and Far East Anti-Plague Institute in the Irkutsk region, may have been due to plague, with many people placed in quarantine. However, unlike the coronavirus responsible for Covid-19, Y. pestis has been known and studied for a long time, and there are available treatments, including vaccines. The WHO, which held a press briefing on October 6, describes the risk as low for the residents of Irkutsk, even lower for the rest of Russia, and extremely low for Europe and the world. Koblentz, however, expressed concerns about the transparency of Russian authorities, noting that it is difficult to trust authoritarian regimes, which foster a culture of secrecy. He stated that the local population is suspicious of government statements, and the rest of the world cannot trust them either, especially in light of China's concealment of data on the potential origin of the coronavirus responsible for Covid-19. The origin of the Black Death has been traced to Central Asian tombs, indicating that plague was present more than 5,000 years ago. Currently, all eyes are on Russia, as the WHO is closely monitoring the incident, and the White House is also monitoring the situation, according to Axios. Martinello added that if the number of cases of pulmonary infection were to increase rapidly and massively, he would be concerned about there being something else at play or that they are dealing with a particular strain of Yersinia pestis, if it is indeed Yersinia pestis.