In a press release, the Health Department said that "Plague has historically been found in wildlife in both states", and that "since 1990, eight human cases were confirmed in OR and two were confirmed in Idaho".
The most common type is the bubonic plague, which represents 80 to 95 percent of cases.
One of the oldest identifiable diseases known to man, the plague is still widely distributed in the warm parts of the world.
According to the state's health department, it is unknown whether the child was exposed to the plague in Idaho, or if the illness was picked up during a recent trip to Oregon. Human-to-human transmission is extremely rare. However, this season, no ground squirrel die-offs or unusual behavior has been reported by state wildlife officials.
Christine Myron, a spokeswoman for the Central District Health Department, said Wednesday that the child, who has not been publicly identified, is back home in Elmore County, Idaho, and "doing well" after being treated with antibiotics in the hospital.
According to the U.S. Centers for Disease Control and Prevention (CDC), the bacteria that causes plague can be found in rodents and fleas.
Sick pets should be examined promptly by a veterinarian, especially if they may have had contact with sick or dead rodents in the desert areas south and east of Boise. The Idaho Central District Health's statement said that since 1990, there have been two cases in Idaho and eight in Oregon.
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Still, the United States only gets a handful of cases - usually between one and 17 every year. Humans get the plague through direct contact with infected animals or fleas.
In wild rodent populations that harbor the bacteria, plague can thrive for a long time before humans come into contact with it.
In the 1400s, approximately 50 million people died of the Black Death.
In the USA, people can contract the plague when disposing of squirrels or mice that died from the infection or traveled to an area where infected animals live. Plague is still one of the scarier infectious diseases out there, with a mortality rate between 30% and 60% if untreated.
It is most commonly transmitted through fleas, which contract the disease from rodents.
According to the most recent data, there were no deaths from plague in 2016, but four in 2015.