A child who was camping in Yosemite National Park has contracted the plague. The California Department of Public Health have launched an investigation and are monitoring other members of the camping party. This case comes in the wake of the recent death of an adult in Colorado who also contracted the incredibly rare disease.

Yes, I’m talking about that plague, the one that killed millions across Europe in the 1300s. While the disease was devastating centuries ago, it’s become incredibly rare since the advent of modern medicine. According to the World Health Organization (WHO), most human cases of the disease have occurred in Africa, but there continues to be scattered cases in the United States. The WHO estimates there were 783 cases, including 126 deaths, reported worldwide in 2013.

California health officials announced on Thursday that the child is currently recovering and that no one else from the camping party has reported symptoms. The last time a human case of the plague occurred in California was in 2006. There have been 42 human cases of plague since 1970 in California, of which nine were fatal.

The plague is caused by the bacteria Yersinia pestis and is mostly spread through the bite of an infected flea, though it can also be spread when the body fluids of an infected animal have contact with cuts or breaks in the skin. The Centers for Disease Control and Prevention report that the plague can take different forms, but the most common are bubonic, pneumonic and septicemic.

The plague is not transmitted from human-to-human contact, unless an infected person has a lung infection and is coughing. The last recorded case of the plague being transmitted in this way in California was in 1924.

Plague-infected animals in California are most likely to be found in the region's foothills and mountains. Health officials regularly monitor these areas by testing animals and flies for infection.  

A person infected with the disease may experience flu-like symptoms such as a high fever, chills and nausea. The plague is treatable with commonly available antibiotics, but there is a case-fatality ratio of 30% to 60% if the disease is left untreated.

“Although this is a rare disease, people should protect themselves from infection by avoiding any contact with wild rodents. Never feed squirrels, chipmunks, or other rodents in picnic or campground areas, and never touch sick or dead rodents. Protect your pets from fleas and keep them away from wild animals,” Director and State Health Officer Dr. Karen Smith said in a statement.  

California health officials are working with the CDC, Yosemite National Park and the U.S. Forest Service to find the source of the infection and to look into the patient’s travel history during the incubation period.