Person in Colorado infected with bubonic plague. Here's what to know.

A person in Pueblo County, Colorado, about 100 miles south of Denver, has been infected with bubonic plague, local health officials said Monday.

Last week, state and local officials identified the case based on preliminary test results. Trysten Garcia, a spokesperson for the Pueblo Department of Public Health and Environment, said in an email Tuesday morning it was bubonic plague. Earlier announcements had been more general, stating it was "plague." The infection was initially reported on Friday. The department said the person was hospitalized for bubonic plague but their condition improved. Because plague is endemic locally, it's hard to pinpoint the source of infection, Garcia said.

Bubonic plague, which wreaked havoc during historic pandemics across Europe and Asia, is caused by the Yersinia pestis bacterium. It is transmitted by fleas often carried by rodents in the wild, including rats and prairie dogs. Plague occurs when infected fleas bite people, or when humans touch or skin an infected animal.

Most human cases in the U.S. have occurred in the Southwest – in northern New Mexico, northern Arizona and southern Colorado – and the West – in California, southern Oregon and far western Nevada. The U.S. has an average of seven human plague cases per year, according to the Centers for Disease Control and Prevention.

In March, a New Mexico man died from plague, state health officials announced. Oregon officials identified a human case of plague in February. The Oregon case likely stemmed from an infected pet cat.

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What are the symptoms of bubonic plague?

Symptoms can develop after an incubation period lasting between a day and a week, according to the World Health Organization. Plague typically causes sudden fever and chills, severe headache, muscle aches, nausea and vomiting.

A common symptom is swollen, painful lymph nodes, called buboes which give the most common form of the disease its name, bubonic plague. These manifest in the body as swelling in the armpits, groin and neck, the Mayo Clinic said. Buboes vary in size from less than half an inch to about 4 inches. Bubonic plague doesn’t spread from person to person, the CDC said.

Other forms of plague include pneumonic, which happens when the bacteria infects the lungs; and septicemic, when the bacteria infects the blood. Pneumonic plague can spread when someone breathes air droplets from an infected person. These droplets can remain in the air an hour after an infected person coughs. Pneumonic plague can also occur when the bacteria from untreated bubonic or septicemic plague spreads to the lungs. Septicemic plague doesn’t spread from person to person.

The WHO estimates that 30% to 60% of people die of bubonic plague. Pneumonic plague is fatal when left untreated.

There is no vaccine for plague in the U.S., the CDC said. People who develop symptoms of plague should immediately see a health provider. Antibiotics can treat plague, but a person must be seen immediately to avoid serious illness or death, said Alicia Solis, a communicable disease and emergency preparedness program manager in the Pueblo County public health department, in a statement.

How can you avoid it?

Wild rodents in the American West commonly carry plague. With that in mind, Pueblo County health officials warned people to clear areas where rodents can hide and breed near homes, garages, sheds or recreational areas. People should not let pets hunt or roam in rodent areas, including prairie dog colonies, and they should treat dogs and cats for fleas regularly. Officials warned that flea collars have not been proven effective against plague-infested fleas. Officials also warned people to avoid letting their pets sleep with them.

People should also avoid contact with dead animals. If you must handle sick or dead animals, use insect repellant with 20 to 30% DEET to protect against fleas, officials said. Use a long-handled shovel to pick up an animal and place it in an outdoor garbage bag.

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'Black Death'

Plague has been found in all continents except Oceania, but the most endemic countries are the Democratic Republic of Congo, Madagascar and Peru. Historically, the disease decimated global populations. In the 14th century, bubonic plague infamously brought the Black Death pandemic, which caused an estimated 50 million deaths, WHO said. More than a quarter of Europe’s population died, although some estimates are higher. Outbreaks later occurred in China and India.

Past U.S. outbreaks, misperceptions

The U.S. has not seen the same level of deaths from plague as other regions, although outbreaks have occurred over the decades. In 1900, plague was introduced on rat-infested ships that sailed from affected areas, causing epidemics in port cities such as San Francisco, where racist public health policies wrongly blamed the Chinese community for bringing disease and being uniquely susceptible to it, as the journalist David K. Randall wrote in “Black Death at the Golden Gate.” In the mid-1920s, Los Angeles had the nation’s largest urban epidemic with more than 30 deaths. In Southern California at the time, public health officials blamed the “Mexican district” just east of downtown.

But plague-infested fleas on urban rat species were to blame, and they’d go on to infect rural rodent species in the West with plague to create a reservoir of infestation that continues to this day.

This article originally appeared on USA TODAY: Bubonic plague infection in Colorado person. What are the symptoms?