Campgrounds in southern California were shut down this week after a trapped ground squirrel tested positive for the plague, Los Angeles County health officials said.
Parts of the Los Angeles National Forest were closed as of 1 p.m. on Wednesday, including Broken Blade, Pima Loops and Twisted Arrow, the Los Angeles Times reported. An advisory from Jonathan E. Fielding, head of the Department of Public Health, said the areas will be closed for at least a week.
"Plague is a bacterial infection that can be transmitted to humans through the bites of infected fleas, which is why we close affected campgrounds and recreational areas as a precaution while preventive measures are taken to control the flea population," the advisory said.
Rodents with a bacterial infection from Yersinia pestis are bitten by fleas. When those fleas bite humans, the human contracts the bubonic plague.
The advisory tells campground visitors to take precautions and avoid feeding animals so they are not exposed to fleas. They advise visitors to wear the insect repellant DEET on their body.
Ground squirrels in the San Gabriel Mountains have been known to have the plague. Officials said the squirrel population in the affected zone will be dusted for flears.
"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," Fielding wrote.
The plague wiped out 60 percent of the population in Europe from 1348 to 1420. Some scholars theorize the plague – called the Antonin Plague in 165 A.D. – was brought home by soldiers from the Persian Gulf and led to the fall of the Roman Empire.
According to the Centers for Disease Control and Prevention, there are seven cases of plague each year in the United States. The illness has a rapid onset.
“Patients develop sudden onset of fever, headache, chills and weakness and one or more swollen, tender and painful lymph nodes [called buboes],” reports the CDC. “This form usually results from the bite of an infected flea. The bacteria multiply in the lymph node closest to where the bacteria entered the human body. If the patient is not treated with the appropriate antibiotics, the bacteria can spread to other parts of the body.”