DENVER – The parents of 7-year-old Sierra Jane Downing thought she had the flu when she felt sick days after camping in southwest Colorado.

It wasn’t until she had a seizure that her father knew something was seriously wrong and rushed her to a hospital in their town of Pagosa Springs. She had a 107-degree fever, and doctors were baffled by the cause.

“I didn’t know what was going on. I just reacted,” Sean Downing said. “I thought she died.”

The Downings eventually learned their daughter was ill with one of the last things they would have thought: bubonic plague, a disease that wiped out one-third of Europe in the 14th century but is now exceedingly rare — it hasn’t been confirmed in Colorado since 2006 — and treatable if caught early.

Federal health officials say they are aware of two other confirmed and one probable case of plague in the U.S. so far this year — an average year. The other confirmed cases were in New Mexico and Oregon, and the probable case also was in Oregon. None was fatal.

Plague is generally transmitted to humans through the bites of infected fleas but also can be transmitted by direct contact with infected animals, including rodents, rabbits and pets.

Darcy Downing said her daughter may have been infected by insects near a dead squirrel she wanted to bury at their campground on U.S. Forest Service land, even though Darcy had warned her daughter to leave it alone. She remembered catching her daughter near the squirrel with her sweat shirt on the ground. Her daughter later had the shirt tied around her torso, where doctors spotted insect bites.

Officials with the Centers for Disease Control and Prevention acknowledged that a series of frightening illnesses linked to insects and pests have been surfacing lately across the country, including mosquito-borne West Nile virus outbreaks in Texas and deadly hantavirus cases linked to Yosemite National Park. But with some of the illnesses — like plague — this is not an unusually bad year; it’s just getting attention.

In Sierra Jane’s case, a Pagosa Springs emergency room doctor who saw her late on Aug. 24 called other hospitals, some of whom thought she’d be fine the next day, before the girl was flown to Denver, Sean Downing said.

There, a pediatric doctor at Rocky Mountain Hospital for Children got the first inkling that Sierra Jane had bubonic plague. Dr. Jennifer Snow suspected the disease based on the girl’s symptoms, a history of where she’d been, and an online journal’s article on a teen with similar symptoms.

Dr. Wendi Drummond, a pediatric infectious disease specialist at the hospital, agreed and ordered a specific antibiotic for Sierra Jane while tests were run, later confirming their rare diagnosis.

It was the first bubonic plague case Snow and her colleagues had seen. “If she had stayed home, she could’ve easily died within 24 to 48 hours from the shock of infection,” Snow said.