Plague (Yersinia Pestis)
Key points
- Yersinia pestis is a species of bacteria that causes plague, an infection that leads to death quickly and that has caused several major epidemics in Europe and Asia over the last 2,000 years.
- Plague occurs in three different forms — bubonic, septicemic and pneumonic.
- Because plague is so rare in the United States, a physician at first may miss the diagnosis, especially if the person becomes ill outside the Southwestern United States.
- With proper antibiotic treatment, most symptoms of uncomplicated bubonic plague will subside within two to five days, although swollen buboes can remain for several weeks.
What Is It?
Yersinia pestis is a species of bacteria that causes plague, an infection that leads to death quickly and that has caused several major epidemics in Europe and Asia over the last 2,000 years. One of the best known was called the Black Death because it turned the skin black. This plague epidemic in the 14th century killed more than one-third of the population of Europe within a few years. In some cities, up to 75 percent of the population died within days, with fever and ulcerated swellings on their skin.
The last urban plague epidemic in the United States occurred in Los Angeles in 1925. Since then, an average of 13 cases of plague have been diagnosed each year, primarily in the Southwest, with about 80 percent occurring in the desert areas of New Mexico, Arizona or Colorado and about 9 percent in California. Worldwide, up to 3,000 cases of plague are reported to the World Health Organization each year.
Plague affects many species of wild rodents, and it usually is transmitted by the bite of infected rat fleas (Xenopsylla species). Less commonly, humans become infected in other ways: 1) when the organism enters through a break in the skin after direct contact with the tissue or blood of an infected animal (for example, if a hunter is skinning an animal) or 2) by direct inhalation of infected droplets if they are in close contact with a person or animal infected with the pneumonic form of the illness (plague infection of the lungs).
In the United States, plague usually is transmitted in one of four ways:
- Contact with infected wild rodents, especially ground squirrels, rock squirrels, prairie dogs or chipmunks
- Contact with carnivores (especially pet cats) that eat these wild rodents
- The bite of a flea that lives on one of these animals
- Scratches or bites from infected pet cats
People who are most likely to be infected include hunters, veterinarians and those who camp or hike in areas where animals are infected with plague. Domestic cats or dogs also can spread the disease to their owners by bringing infected fleas into the home. In the United States, 78 percent of plague infections occur after a flea bite, and 20 percent develop after direct contact with an infected animal (touching a carcass, skinning a dead animal). Another 2 percent occur after inhaling airborne droplets that contain Y. pestis bacteria from an animal that has plague infecting the lungs.
Symptoms
Plague occurs in three different forms — bubonic, septicemic and pneumonic. In each form, Y. pestis bacteria are transmitted in a different way, and they cause slightly different symptoms:
Written and revised by
Andrey Nailor, M.D.
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