A squirrel found to be infected with the plague has caused parts of a national forest in California to be evacuated and shut down.
Campsites in sections of the Angeles National Forest have been closed while more squirrels are tested for the infection.
Los Angeles health authorities have decided to keep the park open only for those hiking through. In the meantime the campsites will remain closed.
Visitors who do decide to take the risk are being advised to use insect repellent and make sure their pets are wearing flea collars.
Although its been centuries since the plague - known as the Black Death - killed in large numbers, the very mention of it can still strike fear into people.
The bacterial infection killed as many as 25 million people in Europe during the Middle Ages and although today it can be treated successfully with antibiotics, it remains a serious condition. If left untreated, victims can die within four days.
The infected squirrel in the Angeles National Forest was discovered during a routine check.
It is believed that no human in the area has been infected.
Chief of Los Angeles County Department Public Health, Dr Jonathan Fielding, said in a statement: "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."