Plague is a serious bacterial infection that's transmitted by fleas. Known as the Black Death during medieval times, today plague occurs in fewer than 5,000 people a year worldwide. It can be deadly if not treated promptly with antibiotics.

The organism that causes plague, Yersinia pestis, lives in small rodents on every continent except Australia. The organism is transmitted to humans who are bitten by fleas that have fed on infected rodents or by humans handling infected animals.

The most common form of plague results in swollen and tender lymph nodes — called buboes — in the groin, armpits or neck. The rarest and deadliest form of plague affects the lungs, and it can be spread from person to person.

Symptoms Causes Risk factors Complications Prevention

Plague is divided into three main types — 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 buboes — swollen lymph nodes — which typically develop within a week after an infected flea bites you. Buboes may be:

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

Other 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
  • 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 sputum
  • Difficulty breathing
  • High fever
  • Nausea and vomiting
  • Weakness

Pneumonic plague progresses rapidly and may cause respiratory failure and shock within two days of infection. If antibiotic treatment isn't initiated within a day after signs and symptoms first appear, the infection is likely to be fatal.

When to see a doctor

Seek immediate medical attention if you begin to feel ill and have been in an area where plague has been known to occur. This includes parts of several states in the western portion of the United States — primarily New Mexico, Arizona and Colorado.

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