Plague is still reported in a small number of countries, but no confirmed case has been identified in Siberia. The World Health Organization says it is seeking more information from Russia about the death of a worker at an anti-plague institute.
Plague is caused by the bacterium Yersinia pestis, which usually circulates among small mammals and their fleas. The World Health Organization says most human cases reported in 2019–2025 came from the Democratic Republic of the Congo and Madagascar. The U.S. Centers for Disease Control and Prevention reports an average of about seven human cases a year in the United States.
Fresh concern followed unconfirmed reports that a staff member at a research institute in Irkutsk had died. WHO said it did not yet know the cause of her death and had asked Russian authorities for more information. Russia’s public health watchdog told the agency that no plague cases had been recorded in the region. The death itself therefore does not establish that an outbreak has occurred.
Plague has three main clinical forms. Bubonic plague, the most common, is usually transmitted through the bite of an infected flea and causes painful swelling of the lymph nodes. Pneumonic plague affects the lungs and can spread between people through respiratory particles, especially during close contact. Septicaemic plague affects the bloodstream.
Pneumonic plague can progress quickly. WHO says symptoms may appear in less than a day. Without prompt treatment, the disease can be fatal within 18 to 24 hours after symptoms begin. Antibiotics are effective when the disease is diagnosed early, making rapid recognition and treatment essential.
Plague is not confined to the Middle Ages. The Black Death pandemic killed more than 50 million people in Europe in the 14th century, but the bacterium remains in natural reservoirs. Human-to-human transmission requires pneumonic infection and close contact. Any suspected case still needs laboratory testing and medical monitoring.