Plague is a severe and potentially deadly bacterial infection which affects rodents, certain animals and humans. Caused by the bacterium Yersinia pestis, the disease cycles among wild rodents such as rats and spreads via their fleas. People are at risk if they are bitten by a flea carrying the bacteria from an infected rodent, if they are scratched or bitten by infected domestic cats or if they handle or skin infected animals such as prairie dogs, squirrels, rats and rabbits.

In the Middle Ages, massive plague epidemics spread through Europe. The “Black Death” killed 50 million people during the 14th century. Plague still occurs in Africa, Asia and South America. It is rare in the United States but has occurred in rural and semi-rural parts of Arizona, California, Colorado and New Mexico.

Plague occurs any time of year; most U.S. cases happen in late spring to early fall. Plague first arrived in the United States in 1900 via rat-infested steamships sailing from affected areas, mostly Asia, causing epidemics in port cities. Today, about seven human plague cases are reported here each year. People of all ages are susceptible, but 50 percent of cases occur in those between the ages of 12 and 45. Worldwide, between 1,000 and 3,000 plague cases each year are reported to the World Health Organization, although the actual number is likely higher.

The use of antibiotics has greatly reduced mortality, which is now about 11 percent; however, plague can still be fatal. It is difficult to assess the mortality rate in developing countries as few cases are reliably diagnosed and reported.

Pneumonic plague, an infection of the lungs, spreads from person to person. When a person or animal, especially a cat, with pneumonic plague coughs, tiny droplets carry the bacteria through the air. Anyone who breathes in these particles may catch the disease; this can start an epidemic.

Symptoms appear suddenly two to three days after exposure and include severe cough, fever, frothy and bloody sputum, pain in the chest or difficulty breathing.

More than 80 percent of U.S. plague cases are bubonic, an infection of the lymph nodes which is not transmitted person to person. Symptoms appear suddenly within two to five days and include chills, fever, a general sick feeling, headache, muscle pain and seizures. A painful swelling of lymph glands called a bubo may appear, commonly in the groin but also in the armpits or neck, frequently at the site of a bite or scratch. Pain may occur before swelling appears.

Septicemic plague, a plague infection of the blood, may cause death before symptoms occur. Symptoms include abdominal pain, bleeding due to clotting problems, diarrhea, fever, nausea and vomiting.

Call your health care provider if you develop symptoms after exposure to fleas or rodents, especially if you live in or visited an area where plague occurs. Tests include culture of the blood, lymph node aspirate (fluid from lymph nodes) and sputum. Preliminary results are available in less than two hours; confirmation takes 24 to 48 hours.

Seek immediate treatment if plague is suspected; death can result if treatment is not received within 24 hours of the first symptoms. About 50 percent of persons with bubonic plague and almost everyone with pneumonic plague dies if not treated. Antibiotics to treat plague include streptomycin, gentamicin, doxycycline and ciprofloxacin. Patients may require oxygen, intravenous fluids, respiratory assistance and supportive care in a hospital critical care unit.

Patients with pneumonic plague should be strictly isolated from caregivers and other patients. All health care staff must wear gowns, gloves and masks and observe strict isolation techniques to avoid accidental contamination and spread of the disease. Anyone in contact with a person with pneumonic plague should be watched carefully and given antibiotics.

Immediately notify local and state health departments so they can investigate and control the problem. There is concern about pneumonic plague being used as a bioweapon since it can spread through an aerosol attack. If bioterrorism is suspected, the health departments will notify the Centers for Disease Control and Prevention, the FBI and other authorities. National and state public health officials stock large supplies of medications which can be sent anywhere in the United States in 12 hours. The U.S. Department of Defense, the CDC, the U.S. Department of Energy and the National Institute of Allergy and Infectious Diseases are working together to develop a vaccine to protect against inhalationally acquired pneumonic plague, as well as antibiotics and interventions to treat and prevent infection.

Although sunlight and drying destroy plague bacteria, it can survive for an hour when released into the air. Currently, no plague vaccine is available in the United States. Rat control and watching for the disease in the wild rodent population are the main control measures.

Concern for travelers is generally low except in rural areas or regions at risk, particularly if camping or hunting or if there is contact with rodents. The three most endemic countries are Madagascar, the Democratic Republic of Congo and Peru. Madagascar experienced an outbreak in November 2014, with 119 confirmed cases, including 40 deaths. The WHO publishes a global alert in response to plague outbreaks.

The content of this article is for informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition.