Scary headlines proclaim the return of the killer bacterial infection. We asked an infectious disease expert to separate the hype from the facts.


Turns out the plague—or Black Death, as it was called by the Europeans who survived this fearsome killer in the Middle Ages—isn’t a disease of the past. In the last two weeks, public health officials have confirmed that fleas in two Arizona counties have tested positive for the infectious disease. The affected counties are Navajo County and Coconino County, where plague-infested fleas were found on prairie dogs near the town of Taylor, the Associated Press reported.

The news comes on the heels of three cases of the plague reported in humans in Santa Fe County, New Mexico, earlier this summer. The first case, identified in a 63-year-old man, was reported in early June. Later in the month, the New Mexico Department of Health confirmed that two women (ages 52 and 62) also had the illness. All three victims spent days in the hospital but have since been released, according to media reports.

The plague, which is caused by the bacterium Yersinia pestis, doesn't usually make headlines, at least not in the United States. The recent infections in fleas in Arizona and in people in New Mexico raise questions—such as how do you even get the plague? And should you be worried about it? We spoke to an infectious disease specialist for answers.

What exactly is plague?

“Plague is a very virulent infectious disease that’s often transmitted from animal host to human by the bite of a flea carrying the bacteria,” explains Claire Panosian Dunavan, professor of medicine emeritus in the division of infectious diseases at the David Geffen School of Medicine at UCLA. “It can also be acquired if a human handles an infected rodent, a common reservoir for the Yersinia pestis bacterium.”

Three types of plague infect humans: bubonic, septicemic, and pneumonic. The bubonic form is the most common type; patients develop "buboes," which are swollen, typically painful lymph glands that become inflamed near the site of the flea bite. From there, bacteria can enter the bloodstream, causing the often-lethal blood infection sepsis.

These three types of plague aren’t mutually exclusive, explains Dr. Dunavan. For example, someone may not notice that they have large buboes before the disease has progressed to their lungs, resulting in pneumonic plague. “All of these complications can occur in different patterns, it just depends on the case,” she says.

Who is at risk?

Everyone, basically—though you have to have been bitten by the bacteria-carrying flea or come into close contact with a rodent who is hosting a carrier flea. Once infected, a person will typically come down with a high fever within a day, and it’s imperative to get medical care as fast as possible, ideally within 24 hours.

Antibiotics are “the most common lifesaving interventions for plague,” says Dr. Dunavan, but they have to be administered in a short window of time or the plague can be deadly. Thanks to antibiotics, it’s unlikely a person will die from plague, if he or she sees a doctor when symptoms first appear.

What precautions should I take?

To stay safe, keep your home and workplace rodent-proof by cleaning up garbage and clutter and getting rid of old firewood, all of which could attract them. Always wear gloves if you’re handling an animal that could be infected, and use flea repellents to safeguard you and your pet if you’re out hiking or camping.

Above all, put plague in perspective, says Dr. Dunavan. “I’m all for people becoming educated about different infectious diseases, but a report reminded me that in 2015, a ‘banner year’ for plague, we had 15 cases and 4 deaths throughout the U.S.,” she says. “That’s a significant mortality rate, but the number of total cases is also quite small. In terms of what kills people day in and day out, plague is very, very rare.”

According to the Centers for Disease Control, plague strikes seven people on average in the U.S. each year, often occurring in Northern New Mexico, where Santa Fe is, as well as parts of Arizona, Colorado, California, Oregon, and Nevada. That's not to say it couldn't happen in other states. But as long as you take a few precautions and see a doctor if you have any reason to suspect you've been infected, there's no reason to panic.