Plague is a severe and potentially deadly bacterial infection.
Bubonic plague; Pneumonic plague; Septicemic plague
Causes, incidence, and risk factors
Plague is caused by the organism Yersinia pestis. Rodents, such as rats, spread the disease to humans.
People can get the plague when they are bitten by a flea that carries the plague bacteria from an infected rodent. In rare cases, you may get the disease when handling an infected animal.
Certain forms of the plague can be spread from human to human. When someone with pneumonic plague coughs, microscopic droplets carrying the infection move through the air. Anyone who breathes in these particles may catch the disease. An epidemic may be started this way. In the Middle Ages, massive plague epidemics killed millions of people.
Today, plague is rare in the United States, but has been known to occur in parts of California, Utah, Arizona, Nevada, and New Mexico.
There three most common forms of plague are:
- Bubonic plague -- an infection of the lymph nodes
- Pneumonic plague -- an infection of the lungs
- Septicemic plague -- an infection of the blood
The time between being infected and developing symptoms is typically 2 to 10 days, but may be as short as a few hours for pneumonic plague.
Risk factors for plague include a recent flea bite and exposure to rodents, especially rabbits, squirrels, or prairie dogs, or scratches or bites from infected domestic cats.
Bubonic plague symptoms appear suddenly, usually after 2 - 5 days of exposure to the bacteria. Symptoms include:
- General ill feeling (malaise)
- High fever
- Muscle pain
- Severe headache
- Smooth, painful lymph gland swelling called a bubo
- Commonly found in the groin, but may occur in the armpits or neck, most often at the site of the initial infection (bite or scratch)
- Pain may occur in the area before the swelling appears
Pneumonic plague symptoms appear suddenly, typically 2 - 3 days after exposure. They include:
- Difficulty breathing
- Frothy, bloody sputum
- Severe cough
Septicemic plague may cause death even before its symptoms occur. Symptoms can include:
- Abdominal pain
- Bleeding due to blood clotting problems
- Low blood pressure
- Organ failure
Signs and tests
Tests that may be done include:
People with the plague need immediate treatment. If treatment is not received within 24 hours of when the first symptoms occur, death may be unavoidable.
Patients with pneumonic plague are strictly isolated from other patients. People who have had contact with anyone infected by pneumonic plague are watched carefully and are given antibiotics as a preventive measure.
Without treatment, about 50 - 90% of those with bubonic plague die. Almost all people with pneumonic plague die if not treated. Treatment reduces the death rate to 50%.
Calling your health care provider
Call your health care provider if you develop plague symptoms after exposure to fleas or rodents, especially if you live in or have visited an area where plague occurs.
Rat control and surveillance of the disease in the wild rodent population are the main measures used to control the risk of epidemics. A vaccination is available for high-risk workers, but its effectiveness is not clearly established.
Gage KL. Plague and other Yersinia infections. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007: chap 333.
Kool JL. Risk of person-to-person transmission of pneumonic plague. Clin Infect Dis. 2005 Apr 15;40(8):1166-72.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.