Campgrounds at the Angeles National Forest were forced to close down following reports that a trapped squirrel tested positive for the bubonic plague, CBS News reported. Though no people have been found to be infected with the plague, the campsite will be restricted as investigations are ongoing and camp officials dust squirrel burrows for fleas.

According to the same report by CBS News, Los Angeles County Department of Public Health chief, Dr. Jonathan Fielding, said in a statement to Reuters, "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."

In the Western United States, the Centers for Disease Control and Prevention reports that there are about 5 to 15 recorded cases of people infected with the plague each year. In the 14th century, about one-third of people in Europe were wiped out by the plague.

Also known as the "black death", the plague is caused by a bacteria called Yersinia pestis, mostly found in rats. Once infected fleas and rodents come in contact with a human through a bite, the disease is contracted.

Though fatal, experts say early detection may save lives.

"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. Admission to the hospital, with respiratory isolation is required," explained Dr. Robert Glatter, an emergency medicine physician at Lenox Hill Hospital in New York City, in a report by CBS News.

The plague manifests in three forms: the bubonic plague, septicemic plague, and pneumonic plague. All are potentially harmful to human health and may lead to death if not properly addressed. Specialized antibiotics and medical treatment are necessary.

Campsites at the Angeles National Forest are expected to be closed to the public for seven days as investigations take place.