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 is 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 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 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 after 2 to 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 can result.
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 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.
Dennis DT, Mead PS. Yersinia species, including plague. In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa.: Elsevier Churchill-Livingstone; 2009:chap 229.
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, Bethanne Black, and the A.D.A.M. Editorial team.