What is plague? 


Plague occurs naturally in the western United States, particularly Arizona, California, Colorado and New Mexico.  The plague bacterium (Yersinia pestis) is transmitted by fleas and cycles naturally among wild rodents.  Plague can also infect humans and their pets.   


How do people get plague? 


  • Bites of infected fleas

  • Touching infected animals (e.g. prairie dogs, squirrels, rats and rabbits)

  • Inhaling droplets from the cough of an infected person or animal   

Common forms of plague:


Bubonic plagueis the most common form of plague.  It usually occurs from the bite of an infected flea.  The key symptom is a swollen, painful lymph node, usually in the groin, armpit or neck.  Other symptoms include fever, chills, headache and extreme exhaustion.  A person usually becomes ill 1 to 6 days after being infected.  If not treated early, the bacteria can spread to other parts of the body and cause septicemic or pneumonic plague.  


Septicemic plagueoccurs when plague bacteria multiply in the bloodstream.  Symptoms include high fever, exhaustion, light-headedness and abdominal pain.  Septicemic plague can quickly cause shock and organ failure.  


Pneumonic plagueoccurs when plague bacteria infect the lungs.  Symptoms include high fever, chills, difficulty breathing and a cough often associated with bloody mucus.  Pneumonic plague is almost always fatal if not rapidly treated.


If you develop symptoms of plague, see a health care provider immediately.

Plague can be treated successfully with antibiotics, but an infected person must be treated promptly to avoid serious complications or even death. 


Protect yourself if you live in an area where plague occurs:


  • Eliminate nesting places for rodents around your property by removing brush, rock piles, trash and excess firewood.

  • Avoid picking up or touching dead animals.  If you must, wear gloves.

  • Regularly treat your dogs and cats for fleas.

  • Do not let pets sleep in bed with you.  This has been shown to increase your risk of getting plague.

  • Use insect repellent that contains DEET to prevent flea bites.

  • Keep pet food in rodent-proof containers.

  • Take sick pets to a veterinarian.

  • Do not allow pets to hunt or roam in rodent habitats.  

Plague in humans:

People become infected with plague bacteria most commonly through the bite of an infected flea.  Infection is also possible when blood or other infected bodily fluid enters into the body through the eyes, mouth, nose, or an open cut.  


People can also be infected by inhaling bacteria from the cough or sneeze of an infected person or animal, such as a cat.  Cats are especially susceptible to plague and, if infected, represent a serious source of potential human exposure.  Dogs are less likely to be ill, but they can still bring plague-infected fleas into the home.

Human plague is often preceded by an outbreak or “epizootic” in which large numbers of susceptible rodents die.  When this happens, hungry infected fleas leave the dead rodents and seek blood from other hosts, including humans and domestic pets.  Studies suggest that in the southwestern United States, epizootics are more likely to occur during cooler summers that follow wet winters. 

For more information, please contact:

Riverside County Department of Environmental Health                

Vector Control Program                                                                                        

800 S. Sanderson Ave. Suite 200, Hemet, CA 92545                                       

(951) 766-9454  ·  (888) 722-4234  · 


Centers for Disease Control and Prevention

 (800) CDC-INFO  ·