A squirrel infected by the plague has closed a California campground for at least a week. No people have been infected by the bubonic plague, also known as the "black death."

A squirrel was captured in a trap on July 16 and tested positive for the bubonic plague, CBS Los Angeles reported.

Three areas in the Table Mountain campgrounds in Los Angeles, including Twisted Arrow, Broken Blade and Pima Loops, have been closed since 1:00 p.m. Wednesday, according to the Los Angeles Times.

"It is important for the public to know that there have only been four cases of human plague in Los Angeles County residents since 1984, none of which were fatal," Los Angeles County Department of Public Health chief, Dr. Jonathan Fielding, said in a statement to Reuters.

About five to fifteen cases of plague in humans occur each year in the western United States, the Centers for Disease Control and Prevention (CDC) reports.

The campground sites will be closed for seven days while squirrel burrows are dusted for fleas.

According to NBC Los Angeles, Dr. Jonathan Fielding, Los Angeles County Director of Public Health and Health Officer, said the infected squirrel "had something like 12 fleas on it."

The last time an infected animal was found was in 2010, CBS LA reported. Squirrels in the surrounding San Gabriel Mountains, according to health officials, had tested positive for the plague in 2010 and 2007, as well as 1996 and 1995, The Daily Mail reports.

Bubonic plague, or the "black death," killed an estimated one-third of Europeans during the 14th century, CBS News reports. The infection is transferred to humans through bites from infected fleas, with symptoms including enlarged lymph glands near the flea bites, fever, and chills. Untreated, the plague can infect the blood and even the lungs, sometimes resulting in pneumonic plague.

If caught early, the infection can be treated easily with antibiotics.

"Early treatment -- within 24 hours of onset of symptoms -- is essential to reduce chances of death in patients with more advanced disease such as pneumonic plague," said Dr. Robert Glatter, an emergency medicine physician at Lenox Hill Hospital in New York City.

L.A. County health officials are urging campers to avoid contact with wild animals, especially squirrels and their burrows, ABC News reports.

Officials also said campers should wear DEET-containing insect repellent to ward off fleas and avoid taking pets into flea-infested areas.