There are about seven cases of the plague each year in the United States, according to the Centers for Disease Control and Prevention. Most are in the West, where the Yersinia pestis bacteria that causes plague lives in rats, squirrels and other rodents and the fleas that infest them.

While the Black Death may have wiped out one-third of Europe’s population in the 1300s, it couldn’t happen today. Antibiotics are an effective treatment. Today, about 90 percent of plague victims who get prompt medical attention survive.

The discovery of the infected squirrel was routine and part of ongoing public-health surveillance, says Ken Gage, chief of CDC’s flea-borne diseases section in Fort Collins.

States where plague is known to exist “are quite good at responding quickly,” Gage says.

In the United States, plague is found regularly in the West. Since 1970, cases have been reported in Colorado, New Mexico, Utah, Arizona, Texas, Nevada, Idaho, California, Oregon and Washington. States where the plague exists began testing rodents for the disease the 1930s, and today have effective programs in place to control it, Gage says.

The plague-infected squirrel in Wrightwood, Calif., was found July 16 by the California Plague Surveillance and Control Program. As soon as tests for plague came back last week, health officials closed three nearby campgrounds in the Angeles National Forest to protect campers. They also posted notices in the area to warn residents to avoid dead animals that might carry fleas, Gage said.

Health officials now will track down the squirrel’s burrows and dust them for the fleas that actually carry the plague bacteria. The campgrounds will be reopened after testing shows they’re plague-free.

The only way to get plague is to be exposed to infected fleas or rodents or to have the plague bacteria get into an open wound or cut, the CDC says. With modern housing and pest control, that’s a lot less common than it was in 1350, when entire villages died from the disease.

About 80 percent of plague cases in the United States occur when people come into contact with infected fleas jumping from dead animals or animal burrows to humans, Gage said.

Last summer, a 7-year-old girl was camping with her family in Colorado and got the plague from a dead squirrel. After weeks in the hospital, she survived.

Plague symptoms include fever, chills, headache, weakness and swollen and tender glands in the neck, underarms or groin.

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