A Los Angeles girl is being treated for plague, which experts think she may have caught in California's Yosemite National Park.
The case is generating headlines, along with two deaths from plague in Colorado, but health officials say the public should not be alarmed. While plague is unusual in the U.S., an average of seven cases are reported every year and people can die from it if they don't get treated.
Colorado officials said Wednesday that an unidentified adult died from plague. A 16-year-old Colorado boy died from plague in June after he developed an unusual and hard-to-treat septicemic infection. Two other Coloradans who caught plague this year were treated and recovered.
Just as in the Middle Ages, when plague swept across Europe and Asia, people catch the bacterial infection from fleas.
Plague is usually easily treated with antibiotics if doctors diagnose it in time. There are three forms: bubonic plague, which affects the lymph glands; septicemic plague, a body-wide infection that can develop if early plague infection isn't treated; and pneumonic plague, which is the only form that spreads from person to person.
Most people who catch it have handled or been near rodents. California officials say they're posting extra signs cautioning people not to feed animals and to stay away from dead animals.
The take-home message: don't feed rodents, don't touch dead rodents and keep your pet away from them.
"Although this is a rare disease, people should protect themselves from infection by avoiding any contact with wild rodents," state health officer Dr. Karen Smith said in a statement.
"Never feed squirrels, chipmunks, or other rodents in picnic or campground areas, and never touch sick or dead rodents. Protect your pets from fleas and keep them away from wild animals."
Pets can carry plague, too. Last year, a pet dog in Colorado caught plague and doctors believe it infected at least four people. Colorado health officials say three cats have tested positive for plague this year, although they are not known to have infected any people.
Symptoms include a sudden fever, a severe headache, nausea and chills. It can feel like flu.
Rodents carry more dangerous diseases than plague. In 2012, three campers in Yosemite died in an outbreak of hantavirus, which has no specific treatment. It was tracked down to mice living in insulated tents.
Plague is a bigger problem globally than it is in the United States. The U.S. was free of plague until about 1900, when steamships brought infected rats across the ocean.
This article originally appeared on NBCNews.com.