Authorities in Oregon have confirmed a case of the bubonic plague in a teenage girl who was believed to have contracted the disease from a flea bite.
Plague is rare and treatable with antibiotics if caught early, but federal authorities have been puzzled by an increase in cases this year.
In a statement, state and local health officials in Oregon said they thought the girl was infected during a hunting trip on Oct. 16 near Heppner, a city located at the foothills of the Blue Mountains in the northeastern region of the state.
She fell ill on Oct. 21 and was hospitalized days later. She is now in the intensive care unit.
There have been no other reported recent cases, the statement said.
Plague is an infectious bacterial disease that is carried by wild rodents and transmitted to their fleas, who then carry the infection to other animals or humans through bites. Symptoms include fever, chills, headache, weakness and a cough.
Bubonic plague affects the lymph nodes. Two other types of plague are septicemic, a blood infection, and the most contagious form, pneumonic, which infects the lungs. It is not transmitted from human to human unless the patient also has a lung infection and is coughing.
Antibiotics can beat all forms of plague if an infection is caught early. Untreated, it is fatal in 66 percent to 93 percent of cases. With treatment, mortality has been reduced to about 16 percent, according to the Centers for Disease Control and Prevention.
In recent decades, an average of seven human plague cases have been reported each year, according to the disease centers. Since April 1, there have been at least 11 cases in the United States of plague in humans, three of them fatal, affecting residents of Arizona, California, Colorado, Georgia, New Mexico, and Oregon, the CDC said in August.
"It is unclear why the number of cases in 2015 is higher than usual," a statement from the disease centers said.
Two of the reported cases were linked to Yosemite National Park.
The statement from Oregon's health authorities said only eight human cases had been diagnosed in the state since 1995, and no deaths have been reported.