Plague is caused by the bacteria Yersinia pestis. Rodents, such as rats, carry the disease. It is spread by their fleas.
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.
A plague lung infection called pneumonic plague can spread from human to human. 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 may be started this way.
In the Middle Ages in Europe, massive plague epidemics killed millions of people. Plague 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.
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 7 days, but may 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 after 2 - 5 days of exposure to the bacteria. Symptoms include:
People with the plague need immediate treatment. If treatment is not received within 24 hours of when the first symptoms occur, death may occur.
Antibiotics such as streptomycin, gentamicin, doxycycline, or ciprofloxacin are used to treat plague. Oxygen, intravenous fluids, and respiratory support usually are also needed.
Patients with pneumonic plague should be strictly 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 people 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 watching for 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.
Dennis DT, Mead PS, Yersinia species, including plague. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 229.
Gage KL. Plague and other Yersinia infections. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007: chap 333.
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.