Ticks are placed in a container to be analyzed in Madrid, Spain, Mar. 16, 2017. Getty Images

Think the plague is just a thing of the past? Think again. Health officials in Arizona confirmed Friday that fleas in one county tested positive for the medieval disease. Authorities in Navajo County said fleas collected from the town of Taylor were sent for testing at Northern Arizona University and found to have been carrying the plague.

“Navajo County Health Department is urging the public to take precautions to reduce their risk of exposure to this serious disease, which can be present in fleas, rodents, rabbits and predators that feed upon these animals,” the department said in a Facebook post Friday.

It’s not the first time the plague has been found in Arizona fleas: Just last week, officials found plague-carrying fleas on prairie dogs in Coconino County.

While the plague gained notoriety in the Middle Ages when it killed millions of people, it’s not unheard of for the bacterium to crop up in the present-day United States. Outbreaks occasionally occur in the southwestern part of the country during cool summers that come after wet winters.

The disease can be transmitted to humans through the bite of an infected flea or through contact with an infected animal. Residents in Arizona were warned to avoid rodent burrows and keep dogs on a leash to avoid coming into contact with the disease.

“An abundance of active prairie dogs doesn’t indicate disease is present,” Najavo County health officials said. “However, a sudden die-off of prairie dogs and rodents may be an indicator of plague.”

Symptoms of the plague typically pop up in an infected person within two to six days of contraction and can include fever, chills, swollen lymph nodes, headache, muscle pain and weakness. The disease can spread to the bloodstream or to the lungs. Modern antibiotics, however, are typically effective in treating it, according to the Centers for Disease Control and Prevention. But without prompt treatment, the plague can turn deadly.

The Navajo County Health Department said it was working to determine what steps it would take to rid the area of plague-carrying fleas. In the meantime, the department outlined precautions residents should take including avoiding sick or dead animals, keeping pets leashed and de-flead, using insect repellents and avoiding rodent burrows, among other things.