American national parks have spectacular scenery enjoyed by hikers worldwide. It’s one way people can enjoy some of the preserved wild places in North America. Due to this intersection of humans and wild animals, a bacterium that is endemic to the southwestern United States has infected a few humans after trips to Yosemite National Park, sparking many news headlines about the plague and closure of a few camping sites for chemical treatment to reduce local flea populations. In total, this summer has seen six cases of infection and unfortunately, three deaths from the plague.
Yersina pestis has never gone away. There are rodents that carry it, fleas that bite the infected animals and spread the bacteria to the next host and thus, the cycle keeps perpetuating itself. This provides an ongoing reservoir of the bacteria is unlikely to ever be eliminated due to rodents being wily little buggers. And if a flea carrying Y. pestis happens to bite a human? After two to six days, symptoms such as fever, fatigue, nausea, and muscle aches appear, and if antibiotics are given within 24 hours of symptoms, Y. pestis infection is easy to treat. Most modern cases are the bubonic plague with swollen lymph nodes, a more localized disease, rather than pneumonic plague that infects the respiratory system and devastated human populations over the last 1,500 years.
In the United States, there are a median number of eight cases a year and the human infections that have been traced back to Yosemite are well within that yearly number. The numbers suggest the risk of picking up the disease is low. To reduce your chances even further, educate yourself about the probability of infection (e.g., Y. pestis is endemic to Colorado, New Mexico, Arizona and California), keep away from rodents whether dead or alive, and use insect repellent on you and any furry companions that might join you on a walk. Although there has not been a human infected by plague in California since 2006, the recent infection of a resident reminds everyone that Y. pestis respects no boundaries and will take its opportunistic chances where it can.
Resources: CDC web site on Plague