Plague never left. The bacterium that caused the Black Death still circulates among wild rodent populations on several continents, and hundreds of people are infected every year. But modern antibiotics have transformed plague from a civilization-ending catastrophe into a treatable infection, and the risk to most people remains extremely low.
Where Plague Still Occurs
The three most endemic countries today are the Democratic Republic of the Congo, Madagascar, and Peru. Since the 1990s, most human cases have occurred in Africa. Madagascar alone reports between 200 and 400 cases per year, mostly in the bubonic form, with a regular epidemic season running from September through April. A 2021 outbreak there killed 8 out of 22 confirmed cases, a fatality ratio of 37%, partly because some developed the more dangerous pneumonic form before reaching treatment.
In the United States, plague became established in western rodent populations after arriving in port cities in the early 1900s. It has persisted in the rural West ever since. Most American cases cluster in two regions: northern New Mexico, northern Arizona, and southern Colorado in one zone, and California, southern Oregon, and far western Nevada in the other. Cases are rare, typically only a handful per year, but they do happen. In January 2024, an Oregon man was hospitalized with confirmed plague, likely transmitted by his infected cat. It was the earliest case in the calendar year Oregon had seen in 90 years of records.
How People Get Infected
The bacterium Yersinia pestis lives in a natural cycle between wild rodents and their fleas. Rock squirrels, prairie dogs, ground squirrels, chipmunks, wood rats, mice, voles, and rabbits all carry it. When an infected flea bites a human, the bacteria enter the body and travel to the nearest lymph node, where they multiply rapidly.
Domestic cats pose a particular risk that many people don’t expect. Cats are highly susceptible to plague and can pick it up by hunting infected rodents or being bitten by infected fleas. They can then pass it to their owners through bites, scratches, or respiratory droplets if the infection reaches their lungs. Dogs are more resistant but can still carry infected fleas into your home. The 2024 Oregon case was linked to close contact with a symptomatic cat.
Three Forms, Three Levels of Danger
Plague presents in three distinct forms, each progressively more serious.
Bubonic plague is the most common. Symptoms appear 2 to 8 days after a flea bite: fever, headache, chills, weakness, and one or more swollen, painful lymph nodes called buboes. Without antibiotics, about two-thirds of people with bubonic plague die. With treatment, that drops to roughly 13%.
Septicemic plague occurs when the bacteria enter the bloodstream, either directly from a flea bite or as a complication of untreated bubonic plague. It causes fever, chills, extreme weakness, abdominal pain, and shock. Skin and tissue can turn black and die, especially on the fingers, toes, and nose. The incubation period is poorly defined but likely just days.
Pneumonic plague is the rarest and most dangerous form. It develops when bacteria reach the lungs, either from an untreated case spreading internally or from inhaling droplets coughed out by an infected person or animal. Symptoms include rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody mucus. The incubation period can be as short as one day. Untreated pneumonic plague is almost always fatal, and it is the only form that spreads person to person.
Why Plague Is No Longer a Mass Killer
Before antibiotics existed, the fatality rate across all forms of plague ranged from 66% to 93%. Today, several antibiotics are highly effective when given early. Treatment dramatically changes the outcome, cutting bubonic plague mortality from roughly two in three to about one in eight. The key variable is speed. People who recognize symptoms early and get to a healthcare provider quickly have a strong chance of recovery.
There is no plague vaccine available to the public. Over 21 candidates are in development worldwide, and seven have completed mid-stage clinical trials, but none has reached general use. For now, prevention and early treatment remain the primary defenses.
Practical Steps to Reduce Your Risk
If you live in, work in, or visit plague-endemic areas of the western United States, a few straightforward precautions go a long way.
- Control rodent habitat. Clear brush, rock piles, junk, and cluttered firewood around your home and outbuildings. Remove food sources like pet food left outdoors and unsecured garbage.
- Rodent-proof your home. Seal gaps and openings where rodents could enter.
- Use flea prevention on pets. Apply veterinary flea control products consistently. Pets that roam freely are more likely to encounter infected animals or fleas. Don’t let free-roaming dogs or cats sleep on your bed in endemic areas.
- Wear repellent outdoors. Products containing DEET work on both skin and clothing. Permethrin can be applied to clothing for longer-lasting flea protection. Follow label instructions.
- Wear gloves when handling wild animals. If you hunt, trap, or come across dead rodents or rabbits, gloves prevent direct skin contact with the bacteria.
If you develop a sudden high fever with painful, swollen lymph nodes after spending time in areas where plague is known to occur, or after contact with a sick or dead rodent, seek medical attention immediately. Early antibiotic treatment is what separates a modern plague case from a medieval one.