Bubonic plague strikes person in Colorado

Six fluorescent yellow tube-like blobs are shown sprawled across an undulating fluorescent green surface
Plague is caused by infection with a particular type of bacterium, illustrated above. (Image credit: SCIENCE ARTWORK/SCIENCE PHOTO LIBRARY via Getty Images)

A person in Colorado has contracted the plague, health officials have confirmed. 

The news came four days after officials announced that there was a suspected case of the disease, based on preliminary test results. In a statement published Tuesday (July 9), The Pueblo Department of Public Health and Environment (PDPHE) then confirmed a "human case of plague in a Pueblo County resident."

In an email to Live Science on July 12, a PDPHE spokesperson verified that the person contracted bubonic plague and not another form of the disease. The exact source of the infection is currently unknown.

Plague is an infection caused by the bacterium Yersinia pestis. This microbe naturally circulates among wild rodents and is transmitted through flea bites. Humans can catch the disease if they are bitten by an infected flea or if they handle the tissue or body fluids of an infected animal, which can include household pets

Related: 'Black death' survivors had plague-resistant genes that may boost their descendants' risk of autoimmune disease

The most common type of plague is known as bubonic plague. In these cases, the lymphatic system, or drainage system that helps rid the body of waste and toxins, becomes infected with Y. pestis. This causes lymph nodes to become inflamed and swell into characteristic "buboes," which give bubonic plague its name. Other symptoms of bubonic plague include a fever, headache and chills, which usually develop within two to eight days after infection. In late stages of the disease, buboes can transform into open, pus-filled sores.  

In some cases, Y. pestis can infect the lungs and cause pneumonic plague, which is considered more severe than bubonic plague. Plague can sometimes start out bubonic and then spread to the lungs, sparking a pneumonic infection. Unlike bubonic plague, the pneumonic infection can be transmitted person-to-person through the air. For instance, a person can catch it if they inhale bacteria-containing droplets that have been expelled by an infected person's coughs or sneezes. However, such transmission has not been reported in the U.S. since 1924

Throughout history, plague has caused widespread pandemics with high casualty rates. The most famous of these was "The Black Death'' in the 1300s, which killed more than 50 million people in Europe

If left untreated, pneumonic plague is always fatal, while untreated bubonic plague has a lower death rate of around 30% to 60%. These days, however, plague can be successfully treated with antibiotics if caught early. 

PDPHE has not yet disclosed how the individual in Colorado is responding to treatment. 

"If you develop symptoms of plague, see a health care provider immediately," Alicia Solis, the program manager of the Office of Communicable Disease and Emergency Preparedness at PDPHE, said in the statement. 

"Plague can be treated successfully with antibiotics, but an infected person must be treated promptly to avoid serious complications or death." Possible complications of plague include meningitis, an infection of the membranes that cover the brain and spinal cord, and septic shock, which results in a dangerously low drop in blood pressure. 

Plague was first introduced into the U.S. in 1900 when infected rats aboard ships sparked outbreaks in port cities. However, no epidemics have been reported in cities since 1925. Nationwide, around seven human cases of plague are reported to the Centers of Disease Control and Prevention every year; more than 80% are the bubonic form of the disease. These infections usually occur in northern New Mexico, northern Arizona, southern Colorado, California, southern Oregon and far western Nevada.

Between 2005 and 2021, 67 cases of human plague were reported in Colorado.

In its latest statement, PDPHE noted several precautionary measures that the public can take to protect themselves against plague. This advice includes eliminating places in the home where rodents can hide and breed, avoiding contact with dead animals and using insect repellent that contains at least 20% to 30% DEET, to help prevent flea bites. 

Editor's Note: The article was updated on July 12, 2024, to confirm that the individual has bubonic plague. 

This article is for informational purposes only and is not meant to offer medical advice.

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Emily Cooke
Staff Writer

Emily is a health news writer based in London, United Kingdom. She holds a bachelor's degree in biology from Durham University and a master's degree in clinical and therapeutic neuroscience from Oxford University. She has worked in science communication, medical writing and as a local news reporter while undertaking journalism training. In 2018, she was named one of MHP Communications' 30 journalists to watch under 30. (emily.cooke@futurenet.com