The Black Plague — yes, the one that killed off close to 60 percent of Europe in the Dark Ages — is still around, and two pet dogs have fallen ill with the bacterial infection. The Bubonic Plague is caused by the bacteria Yersinia pestis, and is spread by fleas present on rodents and rabbits. With proper antibiotic treatment, the infection is curable, but still poses a serious public health threat.

"It is the plague," said Dr. Mark Dimenna from the Environmental Health Department. "It is the bubonic plague, the Black Death. It's the same organism that it always has been."

The disease was unknown in the United States until 1900 when rat-infested ships brought the bacteria to American shores. Since then, 999 human cases have appeared, and most of the cases have been in New Mexico, Arizona, Colorado, Nevada, Oregon, and California.

Health officials in California are also warning people to be careful outside this summer. "Plague is naturally present in many parts of California, including higher elevation of El Dorado County, so we all need to be cautious around animals that can carry it," said Dr. Alicia Paris-Pombo, the county's public health officer.

According to the Centers for Disease Control and Prevention, people develop fever, headache, chills, and weakness, as well as swollen and painful lymph nodes. People can be infected by being bitten by an infected flea or by coming into contact with infected fluids and tissues of a sick or dead animal.