Pneumonic Plague Explained: How Dangerous is the Rare Infection?

Pneumonic plague is a rare but potentially deadly bacterial infection that affects the lungs and, unlike other forms of plague, can spread directly from person to person. Recent concern surrounding a laboratory worker in Russia has brought renewed attention to the disease, but experts stress that modern antibiotics and the relatively limited ease of transmission make today’s situation very different from the plague outbreaks of the past.

What is pneumonic plague?

Plague is caused by the bacterium Yersinia pestis and can appear in several forms.

The most familiar is bubonic plague, which typically affects the lymph nodes. Septicemic plague occurs when the bacteria spread into the bloodstream, while pneumonic plague develops when the infection involves the lungs.

According to infectious disease experts interviewed by CNN, pneumonic plague is considered the most dangerous form because it can cause severe pneumonia and can be transmitted directly between people.

How does it spread?

Unlike bubonic plague, which is commonly associated with infected animals and flea bites, pneumonic plague can spread through respiratory droplets.

Transmission can occur when a person with the disease coughs or sneezes and another person is in sufficiently close contact to inhale bacteria.

However, experts emphasise that pneumonic plague does not spread as easily as respiratory viruses such as Covid-19. Transmission generally requires close and prolonged exposure, making household and healthcare settings more relevant than casual contact.

What symptoms can occur?

Pneumonic plague can resemble other severe respiratory infections, which can make diagnosis challenging.

Symptoms can include fever, chills or shaking, severe coughing and rapidly developing pneumonia-like illness. Imaging of the lungs may show widespread signs of infection.

One important clue is how quickly the illness develops, combined with information about possible exposure to infected animals, rodents, laboratory material or a known case of plague.

Why rapid treatment is essential

Pneumonic plague can become life-threatening very quickly if it is not treated.

The major difference between plague today and during historical epidemics is the availability of effective antibiotics. Experts interviewed by CNN stress that treatment should begin as rapidly as possible after infection or suspected exposure.

Antibiotics may also be given to people who have been exposed to the bacterium in order to prevent the disease from developing.

Why the recent case attracted attention

The disease came back into the spotlight after the death of a 28-year-old researcher at a Russian laboratory that studies plague and other infectious diseases.

Russian authorities described the cause as pneumonia of unknown origin, while reports raised questions about whether the researcher might have been exposed to Yersinia pestis or another dangerous pathogen.

Around 200 people were reportedly placed under medical observation or quarantine as a precaution. Experts interviewed by CNN said that contact tracing and monitoring would be appropriate following a potentially high-risk laboratory exposure.

At the same time, they stressed that important details about the case remained unconfirmed.

Is pneumonic plague still found today?

Although plague is strongly associated with medieval history and the Black Death, the disease has not disappeared.

Cases still occur in different parts of the world, including the United States and Russia. Modern cases are rare, however, and antibiotics have fundamentally changed the prognosis compared with historical outbreaks.

Experts therefore caution against viewing a modern case of plague in the same way as the devastating epidemics that occurred centuries ago.

How concerned should the public be?

CNN’s experts generally emphasise that pneumonic plague is a serious infection but is not easily transmitted through the wider population.

Its ability to spread from person to person makes it more concerning than other forms of plague, but close exposure is usually needed. Modern surveillance, contact tracing and antibiotic treatment also provide tools that were unavailable during historical plague epidemics.

Based on the information available about the recent case, the World Health Organization told CNN that the risk to the general population appeared to be low.

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