A 10-year-old girl's death has been linked to the plague as the rare disease has been recorded in at least six areas of the USA.
Laboratory tests have confirmed that animals and fleas have been detected in La Plata County in Colorado, where the youngster lived.
Plague was also detected in San Miguel, El Paso, Boulder, Huerfano and Adams counties, a spokeswoman for the Colorado Department of Public Health and Environment has confirmed.
Humans typically get plague from fleas carrying the plague bacterium or by handling infected animals, according to the Centers for Disease Control and Prevention.
Jennifer House, deputy state epidemiologist and public health veterinarian for Colorado Department of Public Health and Environment, said: “In Colorado, we expect to have fleas test positive for plague during the summer months.
"Awareness and precautions can help prevent the disease in people.
"While it’s rare for people to contract plague, we want to make sure everyone knows the symptoms.
"The disease is treatable if caught early.
"Let a medical provider know if you think you have symptoms of plague or if you think you’ve been exposed."
Symptoms for the plague include sudden fever, headache, chills, weakness as well as painful lymph nodes.
There is no vaccine for the disease, but it can be treated with antibiotics if detected early.
People are also warned not to touch wildlife, especially dead rodents and rabbits, and keep their pets away from them too.
Two people became infected with plague in the US last year but both survived.
Details about the 10-year-old and how she may have contracted the disease have not been released.
