Prairie dogs can carry plague, and the fleas that live on them can pass it to people. But prairie dogs are rarely the whole story. Most people who get plague are infected by a flea bite, and in Colorado, pet cats and dogs and other rodents are common links too. For prairie dogs, plague is far more dangerous than it is for us. An outbreak can wipe out 90% or more of a colony.
Plague is rare in people, it’s treatable, and a few simple habits lower the risk. Here’s what the record shows.
At a glance
- Cause
- The bacterium Yersinia pestis, spread mainly by fleas
- U.S. cases
- About 7 a year on average (range 0–17), mostly in the rural West
- How people get it
- Flea bites cause about 85% of Colorado cases. Handling sick or dead animals and pets that carry fleas are other routes.
- Treatable?
- Yes, with antibiotics, if started early
- Vaccine
- None available in the U.S.
How people get plague
Plague is caused by the bacterium Yersinia pestis. In the western United States it circulates among wild rodents and their fleas. Colorado’s health department lists fleas, tree squirrels, ground squirrels (including prairie dogs), woodrats and domestic cats as the animals most often involved in human cases in the state.
Flea bites cause about 85% of reported cases in Colorado. Other routes include handling an infected animal, especially skinning one; bites or scratches from infected cats; and, rarely, breathing in droplets from a person or animal with plague in the lungs.
Risk rises during a die-off. When plague sweeps through a prairie dog colony or other rodent population, the hungry fleas leave the dead animals and look for new hosts. Large rodent and rabbit die-offs often come before human cases.
How often it happens
The U.S. averages about seven human plague cases a year, with a range of zero to 17. Most occur in two regions: northern New Mexico, northern Arizona and southern Colorado, and California, southern Oregon and far western Nevada.
A CDC review of every U.S. case from 1970 to 2017 found 482 cases. Three in four were bubonic plague, about one in five septicemic, and 3% pneumonic. Of the 465 patients whose outcome was known, 65 died, or 14%. More than half had contact with animals before getting sick. The most common wild animals were squirrels, prairie dogs and gophers, then rabbits and hares. Skinning an animal was the most common type of contact.
Cases in Colorado
A few Colorado cases show how people actually get exposed:
- 1996, Delta County: A 16-year-old girl died. Investigators concluded she was probably infected while caring for a sick cat.
- 2014, Adams County: Four people developed plague after contact with a dog that had died of it. All four had fever and respiratory symptoms, and one may have caught it from another patient. That would be the first person-to-person spread reported in the U.S. since 1924.
- 2021, La Plata County: A 10-year-old girl died of plague. Plague was confirmed in animals and fleas in the county that summer.
- 2024, Pueblo County: A person was hospitalized with bubonic plague and recovered. The source wasn’t identified.
Where prairie dogs fit
Prairie dog colonies are one of the most visible places plague shows up. In 2019, plague-carrying fleas in black-tailed prairie dog colonies closed parts of the Rocky Mountain Arsenal National Wildlife Refuge and two nearby open spaces. No human cases were reported. In 2025, La Plata County health officials investigated prairie dog colonies that had suddenly gone quiet as a possible plague die-off.
Health officials’ advice during these events is consistent: stay away from the colony and don’t try to kill the prairie dogs yourself. La Plata County warned residents that killing prairie dogs on their property increases the risk of exposure to infected fleas.
For prairie dogs, plague is devastating. It isn’t native to North America, and prairie dogs have little natural immunity. That’s also a problem for the endangered black-footed ferret, which eats prairie dogs and catches plague too. Read more about the wildlife side, including vaccines and flea control, on our sylvatic plague page.
Signs and symptoms
Symptoms usually start two to eight days after exposure. Pneumonic plague can start in as little as a day.
- Bubonic plague, the most common form: sudden fever, headache, chills and weakness, with one or more swollen, painful lymph nodes in the groin, armpit or neck.
- Septicemic plague: fever, chills, extreme weakness, abdominal pain, shock and possible bleeding under the skin. Fingers, toes or the nose can turn black.
- Pneumonic plague, the most serious form: fever, headache and weakness, followed quickly by pneumonia with shortness of breath, chest pain and cough. It’s the only form that can spread from person to person.
If you get sick within about a week of a flea bite, contact with a sick or dead animal, or time near a prairie dog die-off, see a doctor right away and mention the exposure.
Treatment
Plague is treatable with common antibiotics. The CDC tells doctors to start treatment as soon as plague is suspected, without waiting for test results. Gentamicin and fluoroquinolones are the first-line drugs in the U.S., usually for 10 to 14 days. Speed matters. Without treatment, the World Health Organization says bubonic plague kills 30% to 60% of patients and pneumonic plague is always fatal. No plague vaccine is available in the U.S.
How to protect yourself and your pets
- Stay away from prairie dog colonies, rodent burrows and dead animals. Never handle sick or dead wildlife with bare hands. Wear gloves if you must, and call your local health department about disposal.
- Use insect repellent outdoors. DEET works on skin and clothing, and permethrin on clothing.
- Protect pets. Use veterinarian-approved flea control, keep pets out of prairie dog towns, and don’t let pets that roam free sleep in your bed.
- Make your property less inviting to rodents. Clear out brush, junk and messy woodpiles where rodents nest, and don’t leave pet food or wildlife feed outside.
- Report die-offs. If a prairie dog colony near you suddenly goes silent, tell your local public health department.
