Plague is an infectious disease caused by Yersinia pestis bacteria, usually found in small mammals and their fleas. The disease is transmitted between animals via their fleas and, as it is a zoonotic bacterium, it can also transmit from animals to humans.

Humans can be contaminated by the bite of infected fleas, through direct contact with infected materials, or by inhalation. Plague can be a very severe disease in people, particularly in its septicaemic and pneumonic forms, with a case-fatality ratio of 30% - 100% if left untreated.

Types of plague

There are three basic forms of plague:

Bubonic plague

The most common form of the plague is bubonic plague. It’s usually spread by the bite of an infected flea. In very rare cases, you can get the bacteria from material that has come into contact with a person who has the infection.

Bubonic plague infects your lymphatic system (a part of the immune system), causing inflammation in your lymph nodes. Untreated, it can move into the blood (causing septicemic plague) or to the lungs (causing pneumonic plague).

Septicemic plague

When the bacteria enter the bloodstream directly and multiply there, it’s known as septicemic plague. When they’re left untreated, both bubonic and pneumonic plague can lead to septicemic plague.

Pneumonic plague

When the bacteria spread to or first infect the lungs, it’s known as pneumonic plague — the most lethal form of the disease if untreated.

When someone with pneumonic plague coughs, the bacteria from their lungs are expelled into the air. Other people who breathe that air can also develop this highly contagious form of plague, which can lead to an epidemic.

While pneumonic plague can be fatal if left untreated, recovery rates are typically very high if treated within the first 24 hours when symptoms present themselves.

Pneumonic plague is the only form of the plague that can be transmitted from person to person.


Transmission of Y. pestis to an uninfected individual is possible by any of the following means:

  • droplet contact: coughing or sneezing on another person
  • direct physical contact: touching an infected person, including sexual contact
  • indirect contact: usually by touching soil contamination or a contaminated surface
  • airborne transmission: if the microorganism can remain in the air for long periods
  • fecal-oral transmission: usually from contaminated food or water sources
  • vector borne transmission: carried by insects or other animals.


Plague is divided into three main types i.e.,  bubonic, septicemic and pneumonic, depending on which part of your body is involved. Signs and symptoms vary depending on the type of plague.

Bubonic plague

Bubonic plague is the most common variety of the disease. It's named after the swollen lymph nodes (buboes) that typically develop in the first week after you become infected. Buboes may be:

  • Situated in the groin, armpit or neck
  • About the size of a chicken egg
  • Tender and firm to the touch

Other bubonic plague signs and symptoms may include:

  • Sudden onset of fever and chills
  • Headache
  • Fatigue or malaise
  • Muscle aches
  • Septicemic plague

Septicemic plague occurs when plague bacteria multiply in your bloodstream. Signs and symptoms include:

  • Fever and chills
  • Extreme weakness
  • Abdominal pain, diarrhea and vomiting
  • Bleeding from your mouth, nose or rectum, or under your skin
  • Shock
  • Blackening and death of tissue (gangrene) in your extremities, most commonly your fingers, toes and nose

Pneumonic plague

Pneumonic plague affects the lungs. It's the least common variety of plague but the most dangerous, because it can be spread from person to person via cough droplets. Signs and symptoms can begin within a few hours after infection, and may include:

  • Cough, with bloody mucus (sputum)
  • Difficulty breathing
  • Nausea and vomiting
  • High fever
  • Headache
  • Weakness
  • Chest pain

Pneumonic plague progresses rapidly and may cause respiratory failure and shock within two days of infection. Pneumonic plague needs to be treated with antibiotics within a day after signs and symptoms first appear, or the infection is likely to be fatal.


To diagnose plague, your healthcare provider will take a sample of your blood, your spit (mucus or phlegm) or fluid from a lymph node. They’ll send your sample to a lab to look for signs of Y. pestis bacterium.

Note: Rate under the appropriate body system any residual disability of infection.

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