What to know about pneumonic plague after conflicting reports on death in Russia

Thoughts of the plague might conjure up images of masked doctors during the European Middle Ages.

But the deadly disease is back in the spotlight this week, after news about the death of a 28-year-old "anti-plague" research laboratory worker in Siberia spread around the globe.

Local media in Irkutsk, Russia, reported a woman employed at the Irkutsk Anti-Plague Research Institute of Siberia and Far East died last week.

Russian authorities have quarantined part of a hospital and are monitoring her contacts, according to AP.

But state media outlet TASS reported that Russia's public health watchdog, Rospotrebnadzor, confirmed that tests found no pathogens linked to her work and denied any incident at the laboratory.

Uncertainty about what happened at the lab raises questions about how the disease spreads and how to manage it.

Here's what we know.

There are three main clinical forms of plague infection caused by the bacterium Yersinia pestis, which lives in rodents and the fleas that feed on them.

The three strains are: pneumonic, bubonic and septicaemic.

Pneumonic plague, or lung-based plague, is the most virulent form.

Incubation can be as short as 24 hours, and it is transmitted via respiratory particles.

If not treated, it can be fatal.

The bubonic form is the most common and is caused by the bite of an infected flea, which causes bacteria to travel through the lymphatic system to the nearest lymph node where it replicates itself.

At advanced stages, the inflamed lymph nodes can turn into a sore filled with pus called a bubo.

Septicaemic plague occurs when the bacteria enter the bloodstream directly or as a complication of bubonic or pneumonic plague.

Symptoms of this form of plague are fatigue, fever, and internal bleeding.

The Irkutsk Anti-Plague Research Institute of Siberia and the Far East conducts research on plague control, is located at the southern tip of Lake Baikal and was founded by the order of the Council of Labour and Defense of the USSR on June 5, 1934, according to its website.

A state TV station in Irkutsk reported on Monday, local time, that a lab worker, whom it named Darya Shipilova, died last week in a hospital in Shelekhov, a town just outside Irkutsk in Eastern Siberia.

Shelekhov district Mayor Maxim Modin said on Friday the hospital was no longer admitting or discharging patients, and its laboratory halted carrying out routine tests.

Anna Popova, head of Rospotrebnadzor, flew to Irkutsk and met with Governor Igor Kobzev and other officials on Friday.

Kobzev said everyone who came into contact with the woman is under medical supervision.

He didn't identify the infection and called it a suspected case of "a particularly dangerous infection".

US Secretary of State Marco Rubio said on Monday he doesn't think there is cause for alarm, but the United States is watching the case closely.

The most famous outbreak of the bubonic plague was "The Black Death", a pandemic in Europe that lasted from 1346 to 1353.

While historians still debate the Black Death's origin in Europe, it is thought to have arrived on ships carrying rats and fleas, and killed over 50 million people, according to the World Health Organization (WHO).

While the Black Death pandemic is named after the bubonic plague, the pneumonic plague, which had a higher mortality rate, was also believed to have contributed to the pandemic, according to the WHO.

Between 2019 and 2025, the WHO reported 3,847 suspected cases of plague and 423 deaths from 10 countries.

Australia has not recorded a human case since the 1920s.

The US has not recorded a case of person-to-person infection since 1924, according to its Centers for Disease Control.

WHO said the plague is found in animal populations on all continents except Oceania.

Today, bubonic plague is easily treated with antibiotics and the use of standard precautions to prevent acquiring infection.

However, the pneumonic plague has a 100 per cent fatality rate if left untreated.

If patients are diagnosed early, antibiotics and supportive therapy are effective.

If not, the disease can progress rapidly and can be fatal within 18 to 24 hours of infection.

Preventive measures include informing people when animal-detected plague is present in their environment and advising them to take precautions against flea bites and to not handle animal carcasses.

WHO does not recommend vaccination, except for high-risk groups such as laboratory personnel who are constantly exposed to the risk of contamination.

Confirmation of plague requires lab testing.

The best practice is to identify Yersinia pestis from a sample of pus from a bubo, blood or sputum.

A specific Yersinia pestis antigen can be detected by different techniques.

One of them is a laboratory-validated rapid dipstick test now widely used in Africa and South America with the support of WHO.