The Plague Never Went Away: What to Know

A scanning electron micrograph of <em>Yersinia pestis </em>bacteria in the foregut of a flea. Credit - BSIP/Universal Images Group/Getty Images/NIAID

The plague sounds like something out of a history book. But the disease—nicknamed the “Black Death” or “Great Pestilence”—that killed more than 25 million people, about a third of Europe, in medieval times is very much still with us today.

Colorado officials confirmed Tuesday a human case of the plague was detected in Pueblo County. It comes after another human case in Oregon in February.

Caused by the bacterium Yersinia pestis, which is often transmitted by fleas and passed through small animals like rodents or cats, the plague has been responsible for more than 200 million deaths throughout history, dating as far back as 3,800 years ago, according to an article published in the American Journal of Medicine. While the bulk of its casualties came during three major pandemics—in the 6th century in and around Constantinople, in 14th century Europe, and in 19th century Asia—outbreaks have persisted to modern day.

The U.S. Centers for Disease Control and Prevention says an average of seven cases are reported in the country each year, mostly in the western and southwestern states. Globally, there are about 1,000–3,000 cases per year, with the three most endemic countries being the Democratic Republic of Congo, Madagascar, and Peru, according to the World Health Organization.

There are two main forms of plague infection: bubonic, which is caused by a flea bite or blood contact with another infected animal or material and is characterized by swollen lymph nodes or “buboes”; and pneumonic, a severe lung infection caused by inhaling droplets, such as the coughs of infected humans or cats. Over 80% of plague cases in the U.S. have been the bubonic form, according to the CDC, though the pneumonic form is more dangerous.

There is currently no vaccine available in the U.S. that can prevent plague infection, though there are steps you can take, including wearing insect repellent and applying flea control products to pets, to reduce the risk of infection. Today, however, most plague cases don’t result in death because of advances in treatment, including with commonly available antibiotics—though untreated cases can be fatal. The overall risk of death for all types of plague in the U.S., according to Mayo Clinic, is around 11%.

The most important factor for survival is that medical attention begins promptly. Symptoms to watch out for include swollen lymph nodes, sudden fever, head and body aches, weakness, vomiting and nausea, shortness of breath, chest pain, and cough, particularly with bloody mucus.

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