Sierra Jane Downing, a 7-year-old Colorado girl, just survived a battle with a deadly disease that is extremely rare these days, but once wiped out more than a third of medieval Europe: The bubonic plague, or "Black Death." The girl was saved by a quick-thinking doctor at Denver's Rocky Mountain Hospital for Children. The doctor had never treated the potentially lethal bacterial infection, but recognized the mix of symptoms and promptly started treatment. Is this scourge from the 14th century coming back, or is this merely an isolated case? Here, a brief guide:

Is bubonic plague really still around?
Yes, but it's very, very rare. Worldwide, there are 1,000 to 3,000 cases a year, usually in Africa, Asia, and South America. There are 10 to 15 cases in the U.S. every year, according to the Centers for Disease Control and Prevention (CDC). It usually hits in parts of California, northern Arizona, northern New Mexico, or southern Colorado, where the Downing family lives. Still, doctors were caught by surprise by Sierra Jane's sudden illness — there hadn't been a confirmed case of bubonic plague in Colorado since 2006.  

Was it hard for doctors to diagnose?
Yes. At first, Sierra Jane's parents thought she had just come down with the flu. Then her temperature shot to 107 degrees, and she had a seizure. "I didn't know what was going on. I just reacted," her father, Sean Downing, said. "I thought she died." He rushed his daughter to a hospital in a small town in the San Juan Mountains of southwest Colorado. Doctors in the emergency room weren't sure what was wrong, and the girl was flown to Denver, 270 miles away. There, Dr. Jennifer Snow, considering Sierra Jane's symptoms and where she had been recently, came up with the diagnosis of bubonic plague.

What made the doctor suspect the plague?
Sierra Jane had many of the disease's classic symptoms — high fever, chills, headache, tender lymph nodes (or "buboes"), and seizures. (Snow had read an article in an online journal describing a teenager who had similar symptoms.) Another piece of the puzzle fell into place when Snow learned that the Downings had gone camping a few days earlier — the plague usually kicks in two to six days after exposure. Also, Sierra Jane had been near a dead squirrel that she wanted to bury.

What does the dead squirrel have to do with it?
Small rodents — such as rats, mice, and squirrels — can carry the plague. Fleas living on the sick animals can then transfer the disease from rodents to humans. In 14th century Europe, flea-ridden rats infested town after town. And back then, with no way to fight the disease, millions died.

How did the doctor cure Sierra Jane?
Today, if caught early, the plague can be treated effectively with antibiotics, such as streptomycin or tetracycline. If untreated, the shock of infection can cause organ failure and death within a day or two.

Should I be worried about the plague?
Bubonic plague is no joke — but there's no need to panic, says Salt Lake City's Deseret News in an editorial. This isn't the dark ages, and modern physicians can treat the disease quickly and effectively. The problem, in fact, is that the plague is now so rare that many doctors might not suspect it until they've ruled out everything else. "The hardest part of treating the plague is to diagnose it."

Sources: Babble, CBS News, Deseret News, National Institutes of Health