The Three Forms of Plague: Bubonic, Pneumonic, and Septicemic


By Dorsey Armstrong, Ph.D., Purdue University

When we talk of the plague, we tend to think of all the patients being affected similarly, as the infection was caused by the same bacillus. However, what we call the plague actually had three different forms: the bubonic, the pneumonic, and the septicemic. So how were these forms different?

A painting of a man and woman affected with the bubonic plague.
The European plague of the Middle Ages is generally thought of being a bubonic plague, but it had two more forms with different symptoms. (Image: Everett Collection/Shutterstock)

The Bubonic Plague: The Good News

The most common manifestation of the plague was the bubonic form. In most people who caught the plague, large swollen areas developed around the lymph nodes, usually at the neck, groin, and armpits.

These lumps were called buboes in Latin, and so it is from this word that we get the most common name we use for the Black Death: the bubonic plague.

First, let’s check the good news: If you got the bubonic form of the plague, you had around an 18% chance of surviving. While that doesn’t sound terribly encouraging, it’s much better than the chances you had of surviving the two other forms.

In this respect—the chances of survival—the bubonic plague is very similar to a modern zoonotic disease: Ebola.

‘Treatment’ of Bubonic Plague

Signaled by swelling in the neck, groin, and armpit area, human-to-human transmission seems to be almost impossible in the bubonic form of the plague.

Although, it may have occurred in some instances when doctors or caretakers tried to effect a cure by lancing the buboes. First-person accounts of this process indicate that the pus that came out when this operation was performed was disgusting not only in appearance, but also, and particularly, in terms of the smell.

A few accounts relate that the doctor and others in the room were so overcome by the stench that they often fainted or vomited. But, again, this seems to be the one form of plague that you might, just might, survive.

Learn more about the spread of the Black Death in Europe.

The Pneumonic Form of the Plague

Pneumonic plague was the second most common form of plague, and, as the name suggests, it affected the lungs. In this case, the Yersinia pestis bacteria would lodge in the sufferer’s respiratory system, rather than in the lymphatic system, as is the case with the bubonic form.

It started, usually, with a patient zero who’d been infected with the bubonic form of the disease, which then made its way from their lymphatic system into the respiratory system.

What was uniquely terrifying about this form of plague—and that’s not to say that the other forms aren’t also terrifying—is that it was easily transmissible. A doctor or friend or relative taking care of someone infected with the pneumonic form of plague was going to be coming in contact with blood, sputum, and saliva—all containing the bacterium—and they would usually themselves become infected.

This is a transcript from the video series The Black Death: The World’s Most Devastating Plague. Watch it now, Wondrium.

Hazmat Suits and Pneumonic Symptoms

A vintage pamphlet showing a physician with a bird-like mask for protection from the plague
Plague doctors often wore beak-like masks stuffed with herbs, which were thought to prevent the plague infection. (Image: I. Columbina, Paul Fürst/Public domain)

You might imagine that there was no such thing as a hazmat suit to prevent infection in the medieval ages. But, in fact, somewhat by accident, plague doctors did come up with an early form of hazmat suit. The most important part was a birdlike mask that covered the doctor’s face. The beak of this head covering was filled with fresh-smelling herbs and flowers. It was popularly believed that the plague infection was spread due to some sort of bad-smelling miasma, so a lot of people figured if they could hold something sweet-smelling in front of their faces, they could avoid infection.

But, for now, let’s get back to pneumonic plague and the terrifying fact of human-to-human transmission that this form brought with it. Also horrifying was the way one would die: usually because they were drowning in their own blood.

Now the good news here was that from the onset of symptoms to death was usually just two days. The bad news was that the suffering was intense, and the survival rate was less than 1%, and even that statistic might be a tad optimistic. So, if you caught the pneumonic version of the plague, you would die, and die quickly.

The Septicemic Form of the Plague

The third and least common form of plague is known as septicemic, which infected the blood. Like pneumonic plague, this form can start out as bubonic and then the infection can move to a different bodily system.

When plague bacteria enter the bloodstream, they cause something known as disseminated intravascular coagulation, or DIC. In these instances, tiny blood clots start to form throughout the body, which results in something called localized ischemic necrosis, which is just a fancy way of saying that portions of your body tissue start to die off due to lack of circulation.

If you’ve got septicemic plague, and it’s pretty well advanced, your blood starts to lose the ability to clot properly. If your blood doesn’t clot, it starts to seep into other parts of your body, like your skin and internal organs. This produces red and black patchy rashes and bumps on the skin that look rather like lots of pimples, but all over the body.

Learn more about the epidemiology of plague.

Plague and a Quick Death

Most scholars think that these visible indicators are what medieval people meant when they said of a dead person that he or she bore the sign of the plague.

A final common sign of advanced septicemic plague is the vomiting of blood. But, if you’ve contracted septicemic plague, you could die within 24 hours of showing symptoms. In some cases, people were reported as having been feeling fine at nine a.m., not so good at noon, and dead at four.

So, the bubonic form was the most common form, but the least likely to kill you; the pneumonic, though not as common, was not only almost certain to kill you, but was also highly infectious. Finally, the septicemic form of the plague was the rarest, but could kill you within a day of you becoming symptomatic.

Common Questions about Bubonic, Pneumonic, and Septicemic Plague

Q. How did bubonic plague get its name?

Bubonic plague got its name from the most visible symptom of the disease—swellings of the lymph nodes of the neck, groin, and armpits, which were known as buboes in Latin.

Q. How was the pneumonic plague different from other forms of the plague?

Pneumonic plague was the second most common form of plague, and it affected the lungs. This form of plague was easily transmissible, since the bodily fluids such as the blood, sputum, and saliva would carry the infection.

Q. What were the symptoms of septicemic plague?

In septicemic plague, blood would start to lose the ability to clot properly. It would seep into other parts of the body, like the skin and internal organs. This produced red and black patchy rashes and bumps on the skin that looked like pimples.

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