What is pneumonic plague and why is it considered the most dangerous?

A 28-year-old laboratory researcher at a Russian institute dedicated to studying plague and other dangerous pathogens died of pneumonia of unknown origin. The Irkutsk Plague Research Institute is based in Siberia, where a number of other people are under quarantine.

Russia's infectious disease monitoring agency downplayed the link between the researcher's death and her work, but the incident raised questions about what type of plague can cause pneumonia. The US State Department and US Centers for Disease Control (CDC) said they were closely monitoring the situation.

The World Health Organization announced on Monday that it is in contact with the Russian health authorities to verify the incident, and to find out what tests are currently being conducted and any potential repercussions on public health internationally. “Based on available informal information, the public health risk to the general population appears to be low,” a WHO spokesperson said, adding that the organization would update its risk assessment once more information was available.

Pneumonic plague is a rare and fatal lung infection, caused by the bacterium Yersinia pestis. Scientists consider it the most dangerous form of plague infection.

There are other forms of plague caused by the bacteria "Yersinia pestis" and attack different parts of the body. Bubonic plague is the most common form, and often occurs after a flea bite or the bacteria entering through a wound or break in the skin.

The infection causes painful swelling of the lymph nodes and may develop into septicemic plague. Septicemic plague infects the bloodstream, can lead to organ failure, and can also be transmitted directly through the bite of a flea.

As for pharyngeal plague, it affects the throat after eating contaminated meat. Pneumonic plague is the only form of bacterial infection that is transmitted directly from one person to another through respiratory droplets, when an infected person coughs or sneezes.

It can also be transmitted through droplets from infected animals. The last documented case of person-to-person transmission of pneumonic plague in the United States was recorded in 1924, during an outbreak in Los Angeles.

In pneumonic plague, the bacteria settle in the lungs and may cause severe pneumonia, making breathing difficult. Symptoms may begin within 24 hours of infection.

Other symptoms include: Without treatment, the disease is fatal in most cases. Doctors can treat plague with antibiotics for a minimum of 10 to 14 days.

The most commonly used are: Patients who receive antibiotics within the first 24 hours of infection have a better chance of survival. Doctors may also provide supportive treatment, such as oxygen and fluids, while encouraging the patient to rest.

Although plague vaccines have been used since the 19th century, it has not been clear whether they provide protection against pneumonic plague. The World Health Organization does not recommend vaccination, except for the most vulnerable groups, such as laboratory workers who are constantly exposed to the risk of infection.

Why has the plague not been eradicated to this day? People may be most familiar with the plague through literature and history, or using it metaphorically to describe epidemics and poverty, but it still exists today.

The plague was known as the "Black Death" in the fourteenth century, and caused the death of more than 50 million people in Europe. Despite the effectiveness of antibiotics in treating it, the disease is still present on all continents except Oceania, and most human cases since the 1990s have been recorded in Africa, according to the World Health Organization.

The last death from pneumonic plague in America was recorded in July 2025, in Arizona, for a young man believed to have been infected by sick cats. Infectious disease expert Dr. Tyler Evans warns that environmental changes and declining public health measures may increase the risk of plague, but he points out that antibiotics are very effective in treating it.

The World Health Organization said the risk of infection to the general population appears low. People with pneumonic plague feel sick very quickly, which may limit the chances of spreading the infection, according to Dr. Rutul Dalal, an infectious disease specialist at Penn State Health St. Joseph Medical Center.

“It is very difficult for a person to even walk or do their daily activities, let alone travel,” Dalal said. Symptoms may appear within 24 hours of exposure.

He added that there are no direct flights between Russia and the United States, so it is likely that symptoms will appear on the infected person before arriving in the United States. He continued: “Of course, we must be careful and keep this matter in our minds.

The world has become a small village, I say, and we are all interconnected. But at the present time, compared to what we witnessed during the “Covid-19” pandemic, for example, the situation is not of this magnitude yet, and we hope that it will remain limited in this way.

For people who are near plague patients, the World Health Organization recommends avoiding direct contact with infected people, and exercising caution when handling their bodily fluids. Staff caring for pneumonic plague patients should wear usual personal protective equipment and may also take prophylactic antibiotics.

In the event of exposure, health authorities closely monitor family members and other close contacts and provide them with antibiotics before symptoms appear. It also recommends washing hands regularly with soap and water.