When you hear the word plague, it’s easy to imagine dark streets in medieval Europe, black-cloaked doctors, and a disease that wiped out nearly half the population centuries ago. But here’s the shocking truth: plague is not a relic of history. It still exists today—and it has been confirmed in Arizona, California, and New Mexico in 2025.
The recent cases have startled many people who assumed plague had vanished long ago. In reality, the bacteria that cause the disease—Yersinia pestis—have never gone away. They live quietly in the wild rodent populations of the American Southwest, carried by fleas that can occasionally bite humans and transmit the infection. While cases are rare, their appearance in three states this year raises an urgent question: is plague spreading in the United States?
Where the Cases Are Showing Up
So far this year, health departments have reported confirmed plague infections in Arizona, California, and New Mexico:
- In California, a camper near Lake Tahoe tested positive after likely being bitten by an infected flea. Officials later confirmed that dozens of wild rodents in the region had evidence of plague.
- In New Mexico, a man in Valencia County fell ill with plague, marking the state’s first human case of 2025.
- In Arizona, officials announced earlier this summer that plague bacteria were detected in prairie dog colonies, with at least one suspected human exposure under investigation.
These are not isolated, freak events. Instead, they are part of an ongoing pattern. On average, the U.S. reports about seven plague cases every year, most of them in the rural West.
Why Plague Still Exists
The reason plague hasn’t disappeared is simple: nature holds onto it. Wild animals such as prairie dogs, squirrels, chipmunks, and rats serve as reservoirs for Yersinia pestis. Fleas bite these animals, pick up the bacteria, and then can transmit it to humans—or to household pets who later come into contact with people.
For most Americans, the idea of plague seems like something out of a horror story. But for public health experts in the Southwest, it’s a well-known reality. The disease simmers at low levels in the environment, flaring up occasionally when people or pets cross paths with infected fleas.
How Dangerous Is It?
Make no mistake: plague is dangerous. Without treatment, it can be deadly. There are three main forms:
- Bubonic plague, the most common, causes painful swollen lymph nodes, fever, and chills.
- Septicemic plague spreads in the bloodstream and can cause shock and organ failure.
- Pneumonic plague, the rarest but most severe, infects the lungs and can be transmitted person-to-person through respiratory droplets.
The good news is that unlike in medieval times, plague is highly treatable today with antibiotics. When caught early, patients usually recover fully. That’s why awareness and prompt medical attention are critical.
Is It Spreading?
Here’s the key point: plague is not spreading person-to-person in the U.S. Instead, it lingers in the environment, and sporadic cases appear when unlucky encounters happen with fleas or infected animals.
So while plague has now been detected in three states in 2025, experts stress that this doesn’t mean a nationwide epidemic is underway. Instead, it’s a reminder that plague never left the Southwest and that people living in or traveling to these regions should take precautions.
What You Can Do
Health officials recommend a few commonsense steps:
- Avoid contact with wild rodents such as squirrels, prairie dogs, and chipmunks.
- Use insect repellent when hiking or camping in affected regions.
- Keep pets safe—don’t let cats or dogs roam freely in rodent habitats where they can pick up infected fleas.
- Seek medical care immediately if you develop sudden fever, chills, and swollen lymph nodes after possible exposure outdoors.
The Bottom Line
The word plague carries enormous fear, and for good reason—it once reshaped human history. But while the disease still exists, it does not pose the same catastrophic threat today. Cases in Arizona, California, and New Mexico show that plague is still quietly circulating in the American Southwest.
Should you be concerned? Yes, enough to be informed and cautious. But should you panic? No. Thanks to antibiotics, vigilant public health systems, and modern science, the plague is no longer the unstoppable force it once was.
Still, its presence is a chilling reminder: sometimes the most ancient threats are closer than we think.
