Before this year, the last time a human case of plague was reported in the Yosemite Valley was in 1959.
Now, the California Department of Public Health is investigating a second case of plague it believes was contracted by a Georgia native during a recent visit to Yosemite National Park. It comes nearly two weeks after health officials announced a child had contracted it while visiting the park with family in mid-July.
The health department has contacted the park, the National Forest Service and the Centers For Disease Control and Prevention to examine areas where the person from Georgia visited.
Despite its reputation as a mass killer of humans throughout history, plague — which wiped out about 30% of the European population in the 1300s — has become a vastly more reliable killer of wildlife than people. It nearly eradicated the black-footed ferret and prairie dogs in the U.S.
Modern medicine has mostly eliminated the threat to humans from plague, said Dr. Danielle Buttke, epidemiologist for the National Park Service.
In California, there have been 42 human cases of plague since 1970, and nine were fatal.
Health officials are warning the public about the risk of the infectious disease spread by fleas.
"The California Department of Public Health and Yosemite National Park were very proactive in their campaign to educate visitors about plague," Dr. Karen Smith, director of the state health department, said in a statement. "Warnings issued in California regarding plague were useful all the way across the country in Georgia. Those warnings helped the patient get the prompt medical attention necessary to recover from this illness."
After evidence of the plague was discovered, health officials closed two park campgrounds in Yosemite National Park.
The infected child, who lives in Los Angeles County, was camping with family at the Crane Flat Campground. The campground was closed for four days and reopened Friday.
Several squirrels and chipmunks were trapped and combed for fleas during an environmental survey of the campground. The fleas tested positive for plague.
The Tuolumne Meadows Campground closed at noon Monday after the plague was discovered in two dead golden-mantled ground squirrels. The campground is scheduled to reopen at noon Friday.
Rodent burrows at the campgrounds were dusted with a flea insecticide to kill any remnants of plague.
Symptoms of plague may include high fever, chills, nausea, weakness and swollen lymph nodes in the neck, armpit or groin. If left untreated, it can be fatal.
Knowing the symptoms and seeking prompt treatment is critical to surviving the disease, Buttke said. Chances of survival also depend on how the person contracted the disease. Inhaling the bacteria, which is rare, can aggravate symptoms and the disease can spread to the lungs quickly, she said.
Plague-infected animals usually are found in the foothills and mountains and sometimes along the coast of California.
In 2014, plague activity was detected in animals in El Dorado, Mariposa, Modoc, Plumas, San Diego, Santa Barbara and Sierra counties.
There has been a recent reemergence of plague in humans in the Western U.S., which is unusual, Buttke said.
Health officials don't know what is causing the outbreak, she said. Drought is probably not a factor, Buttke said, because unlike the parched conditions in California, Colorado has been wet. In Colorado, the plague was blamed for the deaths of two people this year.
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