Justin Sullivan/Getty Images A child falls ill with the plague while camping in California’s Yosemite National Park.

“When an infected rodent becomes sick and dies, its fleas can carry the infection to other warm-blooded animals or humans”, reads as statement put out Thursday by the state Department of Public Health. In June the Denver Post reported on the septicemic plague death of a Larimer County, Colorado high school athlete.

Plague is an infectious disease caused by bacteria carried by wild rodents, including chipmunks and squirrels, and their fleas. Test results on the child came back positive for the disease on Wednesday.

Most recently, an unidentified person from Pueblo County, Colo., died from the plague on Tuesday. Proximity to certain plant habitats endemic to the West, such those dominated by juniper and pine, also amp up plague risk.

An estimation of the “plague line” in the American West. To the west of the plague line, outbreaks happen. It corresponds with the 100th meridian longitudinally, along with prairie dog habitats.

A child from Los Angeles County has been diagnosed with human plague. “We typically have an average of seven cases in the United States every year”.

“They have dispersed throughout the western U.S. and there is a rough “plague line” where cases occur, based on rodent migration patterns”, he says. The U.S. was free of plague until about 1900, when steamships brought infected rats across the ocean.

California health officials are looking into a case of the human plague.

But … didn’t this die out in the Middle Ages? People who develop these symptoms should seek immediate medical attention and notify their health care provider that they have been camping or out in the wilderness and have been exposed to rodents and fleas. Searching for fresh blood, fleas abandon their dead animal hosts and bite humans.

Most people who catch it have handled or been near rodents.

It was the second fatal case of plague in Colorado in less than three months. The last case of such a transmission in California occurred in 1924.

In California, infected animals will likely be found in the mountains, foothills and sometimes the coast. Signs embrace enlarged lymph glands close to the flea chew, fever and chills, based on the federal Facilities for Illness Management Prevention.