How Did Two Yosemite Park Campers Catch the Plague?

In the last three weeks, two separate cases of human plague have been reported in visitors to Yosemite National Park. Luckily, both the child from Los Angeles who became ill last month and the unidentified visitor from Georgia who recently contracted the plague are reportedly recovering.

The plague is probably one of the most alarming-sounded infections out there, at least for anyone who has taken a sixth-grade history class, but are these two cases any cause for concern?

How did these two people get the plague?

The California Department of Public Health (CDPH) says both people were probably infected by a flea bite. The plague is caused by a bacteria called Yersinia pestis that mostly infects small animals and their fleas, and two dead squirrels found in the park tested positive for plague. As a precaution, the public health department has temporarily shut down the campground where the squirrels were found to spray for fleas around rodent burrows.

How does it spread?

The most common type of plague, bubonic, can't be spread from person-to-person. The only way to contract it is to be bitten by a flea carrying the bacteria or by handling the body of an infected animal. Pneumonic plague, a rarer form, can be spread person-to-person if you inhale infected droplets that the sick person has coughed up.

How dangerous is it? Will these people die?

Not likely. The plague is a serious illness and it can kill, but if treated early, patients these days often recover. There are actually three kinds of plague, and two are more life-threatening than the other. Bubonic plague, the most common form, is an infection of the lymph nodes, and is less dangerous. Pneumonic plague is an infection of the lungs and septicemic plague is an infection of the blood. Earlier this year, a Colorado teen and an unidentified adult both died after becoming infected with septicemic plague.

Do lots of people get the plague? Is this common?

No, human plague is quite rare in the US these days, though it's not unheard of. In fact, the last time there was a case of human plague in Yosemite was 1959. The Centers for Disease Control and Prevention says there are an average of seven cases of human plague reported in the US each year, though some years it's as many as 17. These two cases, and the two in Colorado, are the only ones that have been reported so far this year.

Is this a plague outbreak?

For the squirrels in Yosemite, maybe, although only two that died after being infected with the disease have been found. Among humans, no. The plague usually infects a handful of Americans each year.

How can I avoid catching the plague?

The CDPH and the CDC both have a few tips to protect yourself if you're going to be hanging out, hiking, or camping in rural areas this summer, particularly in the western states (there was only one case of the plague east of the Mississippi between 1970 and 2012):

• don't touch, feed, or get too close to rodents like squirrels, even if they look healthy
• wear long pants tucked into your socks or boots (so stylish, I know)
• use insect repellent with DEET, so if an infected flea does come close, it will be less likely to bite you
• be careful with pets: cats can get the plague and spread it to humans by coughing up bacteria-laced droplets, while both dogs and cats can carry plague-infected fleas