Plague is a severe and potentially deadly bacterial infection.
Plague is caused by the bacteria Yersinia pestis. Rodents such as rats carry the disease. It is spread by their fleas.
People can get plague when they are bitten by a flea that carries the plague bacteria from an infected rodent. In rare cases, people get the disease when handling an infected animal.
Plague lung infection is called pneumonic plague. It can be spread from person to person. When someone with pneumonic plague coughs, tiny droplets carrying the bacteria move through the air. Anyone who breathes in these particles may catch the disease. An epidemic can be started this way.
In the Middle Ages in Europe, massive plague epidemics killed millions of people. Plague has not been eliminated. It can still be found in Africa, Asia, and South America.
Today, plague is rare in the United States. But it has been known to occur in parts of California, Arizona, Colorado, and New Mexico.
The 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 8 days. But the time can be as short as 1 day 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 2 to 5 days after exposure to the bacteria. Symptoms include:
- Fever and chills
- General ill feeling (malaise)
- Muscle pain
- Smooth, painful lymph gland swelling called a bubo that is commonly found in the groin, but may occur in the armpits or neck, most often at the site of the infection (bite or scratch); pain may start before the swelling appears
Pneumonic plague symptoms appear suddenly, typically 2 to 3 days after exposure. They include:
- Severe cough
- Difficulty breathing and pain in the chest when breathing deeply
- Frothy, bloody sputum
Septicemic plague may cause death even before symptoms occur. Symptoms can include:
- Abdominal pain
- Bleeding due to blood clotting problems
People with the plague need immediate treatment. If treatment is not received within 24 hours of when the first symptoms occur, death can result.
People with pneumonic plague must be isolated from caregivers and other patients. People who have had contact with anyone infected by pneumonic plague should be watched carefully and given antibiotics as a preventive measure.
Without treatment, about 50% of persons with bubonic plague die. Almost everyone with pneumonic plague dies if not treated. Treatment reduces the death rate to 50%.
When to Contact a Medical Professional
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 watching for the disease in the wild rodent population are the main measures used to control the risk of epidemics. The plague vaccine is no longer used in the U.S. New vaccines are being developed.
Bubonic plague; Pneumonic plague; Septicemic plague
Mead PS. Yersinia species (including plague). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 231.
Shandro JR, Jenkins JG. Wilderness-acquired zoonoses. In: Auerbach PS. Wilderness Medicine. 6th ed. Philadelphia, PA: Elsevier Mosby; 2012:chap 59.
Update Date 5/1/2015
Updated by: 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, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.