It's a disease carved into human history, with a deadly reputation.
"The plague is basically what's been here for centuries," said Medical Expert Dr. John Torres, in an interview with our sister station KUSA. "It's what caused the Black Death back in the Middle Ages."
Even though it doesn't kill people in large numbers like it once did, it is a serious disease. One man from Adams County is in the hospital recovering from a form of Plague.
The disease is part of the fabric of nature in Colorado now, found in rodents-- mainly prairie dogs. It's transmitted through the fleas they carry.
"When the prairie dogs actually die, the fleas need somewhere to go. So once there is a prairie dog die-off, the fleas are out looking for somewhere to get a meal from," said Jennifer House of the Colorado Department of Public Health and Environment.
In the latest case, doctors discovered the owner of a dog contracted plague. Tests later showed the dog, which had died unexpectedly, also had the disease.
There are three types of plague; all can be potentially deadly, if not treated.
The first is bubonic, which causes lymph nodes to swell. There is also septicemic, which comes about when the plague gets into the bloodstream. Finally, there is pneumonic, which is the kind the patient in Colorado has. Doctors said it can be especially worrisome.
"It's a type of pneumonia," Dr. John said. "It can be spread from person to person, and that's what makes it kind of scary and kind of dangerous."
The Colorado Department of Public Health and Environment said there have been 12 cases of plague in Colorado in the past decade. The last case of pneumonic plague was in 2004.
"In humans, it's actually become fairly rare," House said. "We don't see a lot of cases."
Still, experts said to protect yourself, insect repellent with DEET helps. They also recommend staying away from wildlife and making sure your pets do as well. The key is to make sure fleas that carry plague don't land on you.
To treat the plague, doctors give patients specific antibiotics. As for how exactly the latest patient and the dog contracted the plague, the department of health said that was still under investigation.