Vector-Borne and Zoonotic Diseases Program


prairie dog

What is Plague?

Plague is a disease caused by a bacteria called Yersinia pestis. The first known human case of plague in Arizona occurred in 1950. Since then, there has been an average of 1-2 human cases per year. Plague activity in nature has been known to wax and wane over time, and this is influenced largely by climate conditions and rodent and flea populations. During the years 2001-2006, plague activity was reduced in Arizona, and no human cases of plague were reported. In 2007, plague activity show signs of increasing.

This is the same bacteria that caused the Black Death in the Old World in centuries past. Fortunately, the conditions that produced that outbreak no longer exist and plague is now limited to a few sporadic cases in several western states.

The plague bacteria circulates among rabbits and rodents (such a prairie dogs, ground squirrels, rats and mice). Plague is transmitted from one animal to another by the bite of fleas.

Carnivores, wild and domestic, can contract the disease by eating plague-infected rodents and rabbits. Some carnivores, such as dogs, rarely show symptoms, although cats usually die. This is also true of wild members of the dog and cat families.

Where is plague found?

Plague is found in most areas of Arizona above 4,500 feet in elevation. Its intensity varies from season to season and from place to place. Health officials continually monitor plague activity. Areas with plague activity are reported to the public through posters or news releases.

How does a person get plague?

A person can get plague after being bitten by infected fleas. People can get fleas from:

  • Petting dogs or cats that may carry rodent fleas;
  • Handling wild rodents or rabbits;
  • Venturing too close to rodent burrows or nests, especially prairie dog and ground squirrel burrows.

A person can get plague by coming in direct contact with blood or tissues of infected rodents, rabbits or carnivores, such as during the skinning of game. The bacteria can enter through an open cut or scrape in the skin, or through the mucous membranes of the eyes, nose and mouth.

Most human plague infections initially involve the lymph nodes (this is the bubonic form). Patients with this kind of plague do not represent a risk of transmission to other people. In some people, the plague bacteria can move into the lungs (pneumonic plague). A cough or sneeze from a person with this type of plague illness can spread the disease directly to other people.

How can plague be avoided?

The following precautions can decrease your chances of being exposed to plague.

  • Do not allow pets to roam freely. Fit them with a flea collar or dust them with flea powder on a regular basis making sure to follow all label directions.
  • Avoid contact with sick or dead animals and stay away from rodent burrows.
  • Wear insect repellents to keep fleas away when hiking or working in areas where plague might be active.
  • Wear rubber gloves when skinning and cleaning game animals.

What are the symptoms?

Plague is a serious disease that can be fatal if not treated promptly and effectively. The symptoms of bubonic plague are:

  • Fever
  • Headache
  • Pain or swelling in the groin, armpit or neck area
  • Weakness
  • Nausea (occasionally)

Symptoms usually appear within 2-6 days after exposure with the average being 3 days.

If you have symptoms suggesting plague and a possible plague exposure, see your doctor immediately! Plague is curable if diagnosed and treated early. If your dog or cat has symptoms and an exposure history, notify your veterinarian at once.

Plague Information Resources