The plague, one of the deadliest infectious diseases in human history, continues to exist despite the passage of centuries and advances in modern medicine. Although it is now treatable with antibiotics when detected early, the disease still affects people in different parts of the world, with recent concerns in Russia bringing renewed attention to its continued presence.
The disease came under the spotlight after an employee of the Irkutsk Anti-Plague Research Institute in Siberia died following severe pneumonia. The death triggered concerns after media reports speculated that the employee might have contracted pneumonic plague.
However, Russian authorities told the World Health Organization (WHO) that no plague cases had been recorded in the region and that tests conducted on the deceased employee and identified contacts did not detect the high-risk pathogens under investigation. The exact cause of the death remained undetermined in the WHO’s assessment published on October 10, 2026.
The incident has highlighted a common misconception that plague disappeared after the devastating outbreaks that killed millions of people centuries ago. In reality, the bacterium responsible for the disease continues to circulate naturally among wild animals, particularly rodents, making complete eradication difficult. Plague is caused by *Yersinia pestis*, a bacterium that can infect the lymph nodes, lungs and bloodstream.
It became infamous during the Black Death pandemic in the 14th century, which devastated populations across Europe and other regions. Evidence also indicates that plague-related infections have existed for thousands of years, including in Siberia, where researchers have identified ancient evidence of the disease dating back at least 5,500 years. According to the WHO, most human cases reported between 2019 and 2025 were concentrated in Africa, particularly the Democratic Republic of the Congo and Madagascar.
The infection remains uncommon globally, with an estimated 1,000 to 2,000 cases reported annually. In the United States, around seven human cases are recorded on average each year, primarily in rural areas of the western states. The bacterium generally circulates among animals such as rats and prairie dogs.
Fleas feeding on infected animals can transmit the infection to humans through bites. People can also contract plague through direct contact with infected animal tissues or bodily fluids. The pneumonic form, which affects the lungs, can additionally spread through respiratory droplets during close contact with an infected person.
Plague occurs in three main forms: bubonic, pneumonic and septicaemic. Bubonic plague is the most common and typically causes painful swelling of the lymph nodes, particularly in the groin, armpits and neck. These swellings, known as buboes, may be accompanied by sudden fever, chills, headaches and body pain. Pneumonic plague affects the lungs and can develop after inhaling the bacteria or when an infection spreads from another part of the body. Septicaemic plague occurs when the bacteria enter the bloodstream. Both forms can progress rapidly and become life-threatening without timely medical intervention.
Untreated bubonic plague can also develop into pneumonic or septicaemic plague. The WHO estimates that bubonic plague has a case-fatality ratio of 30% to 60% if appropriate treatment is not provided. Pneumonic and septicaemic plague can also be fatal when left untreated, underlining the importance of early diagnosis and medical care.
Despite its deadly history, plague can be treated effectively with antibiotics if patients receive prompt medical attention. Early treatment is particularly important because the disease can deteriorate rapidly, especially in its lung and bloodstream forms. Preventive measures include avoiding contact with sick or dead animals, controlling exposure to infected fleas and seeking medical advice after a suspected exposure.
Vaccines against plague have been developed, but their use is generally recommended for people at high risk of exposure, including certain laboratory personnel and healthcare workers. Protection against pneumonic plague remains an important consideration in vaccination research and public health planning.
The Siberian incident has also drawn attention to laboratory safety because the deceased employee worked at a research facility handling dangerous pathogens. Russian authorities reported that preventive measures were implemented, contacts were monitored and testing did not identify high-risk pathogens. The WHO said it had found no evidence of ongoing transmission associated with the incident, while noting that the absence of a confirmed diagnosis meant some uncertainty remained.
Experts have cautioned that the continued presence of plague bacteria in wild animal populations means the disease cannot simply be considered a relic of the past. While modern antibiotics and public health surveillance have significantly improved the ability to manage infections, awareness, early diagnosis and timely treatment remain essential to preventing deaths from this historically devastating disease.
