Future Tense

You Do Not Need to Worry About the Bubonic Plague Squirrel in Colorado

A squirrel sitting on a deck ledge eats an acorn.
This Pennsylvania squirrel probably does not have the plague. Caleb Martin/Unsplash

On Monday, public health officials in Morrison, Colorado, announced that a squirrel had tested positive for the bubonic plague, aka the Black Death. In a world attuned to the danger of animal reservoirs for human disease (COVID-19 appears to have jumped species from bats; plague usually hitches a ride from rodent to person in the stomach of a flea), that story was going to raise fears. Sure enough, the plague squirrel has become famous, doubtless hoping to outshine 2015’s breakout rodent, pizza rat. This follows breathless reporting earlier in the month about a human case of plague in the city of Bayannur, China. But the plague threat is overdone—and misplaced. And the squirrel menace lies elsewhere.

The plague has a storied history steeped in mass mortality. Analysis of ancient cadavers suggests an outbreak might have killed much of the population of Europe in 3000 B.C. as people riding newly domesticated—and possibly infected—horses swept in from the Russian steppe and replaced them. It reappeared in the waning years of the Roman Empire and struck down perhaps 9 million people. In the 14th century, the Black Death carried off one-third to half of Europe’s population. And then at the end of the 19th century and into the early 20th, a global pandemic spread from Yunnan, China, to cities including Bombay, Singapore, Buenos Aires, and San Francisco. The disease is generally harbored in rodents—like squirrels, rats, and prairie dogs—and then transmitted via flea bite.

The bubonic plague is a hideous disease. A subheading from one report on the unfortunate Morrison squirrel helpfully notes that symptoms include “sudden high fever, chills, headache, and nausea.” That’s to say nothing of the painful pus-filled swellings in the armpits and groin, muscle cramps and seizures, gangrene, coma, and death. Untreated, mortality rates can reach above 50 percent.

But here’s the good news: Most people who have fever, chills, headache, and nausea are not suffering from bubonic plague. And even if by a 1 in a lot less than a million chance you are down with the disease that helped bring down empires, that’s still OK: We have a cure.

Worldwide, there were only 243 cases of plague and 41 deaths in 2018. “The global incidence of human plague is the lowest reported in 30 years,” suggested the World Health Organization last year. In the U.S., plague does present a real if minor threat to both humans and pets. It has been circulating in the wild in the Southwest for about a century, ever since the global pandemic. There are about seven human cases in the average year. (In parts of the American West, you may come across signs that say, “Caution: Prairie Dogs Have Plague!,” italics and exclamation point in the original.)

As the Centers for Disease Control and Prevention notes, “Plague is a very serious illness, but is treatable with commonly available antibiotics,” which includes streptomycin, gentamicin, levofloxacin, ciprofloxacin, doxycycline moxifloxacin, and chloramphenicol. If you think you might have been bitten by a plague-infected flea, you can take some of these drugs before any symptoms emerge, and that will stop the painful buboes appearing in the first place. In addition, CNN has helpfully reported that, last year, a couple died from plague after eating the raw kidney of a marmot. That suggests part of any household safety plan you develop in response to bubonic squirrel concerns should probably include “don’t eat raw squirrel innards.”

If you want rodent-related existential angst, squirrels armed with bubonic plague rank far below squirrels assaulting our power grids as a threat to national security. In their book Clear and Present Safety, Michael A. Cohen and Micah Zenko report on a database of disruptive attacks against critical infrastructure systems, mostly within the United States. There were 2,436 attacks listed as of mid-2018. Forty-nine percent of those attacks came from squirrels, which is 394 times the number of incidents in the database caused by humans. Headlines about a plague mortality threat similar in magnitude to that presented by paper cuts are missing this far bigger story.

For another unusual animal story, listen to this week’s episode of How To! With Charles Duhigg.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.