Plague is a highly infectious disease caused by bacteria carried by rodents such as ground squirrels, chipmunks, wood rats, and mice. A few ways plague can be transmitted to humans or pet include:

  • Bites from infected fleas
    • Hungry fleas will leave a sick or dead rodent to find new blood meals from humans
  • Direct contact with sick or dead animals
    • Plague bacteria in the blood, urine, or saliva of an infected animal can enter cuts and abrasions on humans
  • Pet involvement
    • Infected rodents fleas can be brought into a home or campsite by a dog or cat
    • Plague pneumonia can be transmitted by a sick cat that is coughing and sneezing

The Vector Control Program routinely collects and tests fleas and blood samples from squirrels in our local mountains and campgrounds. If tests come back positive for plague, park rangers are notified, squirrel burrows may be treated for fleas, and warning signs are posted to inform the public on how to avoid fleas and protect themselves and their pets from this serious disease.

Plague Detections in San Diego County

symptoms of plague




Symptoms include chills, fever, headache, muscle aches, weakness, and most commonly swollen and tender lymph nodes (called buboes). This stage is called the bubonic plague. Plague symptoms usually appear 2 to 6 days after infection. Plague is treatable when found early.

An animal with plague will become very ill, may stop eating and will have a fever. Swollen lymph glands may occur, generally in the neck area.

Inform your veterinarian if a pet becomes sick following a visit to a plague area. 


  • Avoid known plague areas.
  • Use flea control products on pets.
  • Avoid contact with wild animals and their fleas, especially sick or dead rodents.
  • Use caution when handling a sick pet that has been in a plague area.
  • Avoid face-to-face contact with sick pets or sick humans.
  • Report sick or dead animals to park rangers or the Vector Control Program.
  • Contact a physician immediately if you become ill within 7 days of being in a plague area.
plague warning at trailhead


  • State and local vector control programs monitor plague activity. Rangers and park employees are trained to watch for sick or dead rodents. 
  • The Vector Control Program routinely collects and tests fleas and blood samples from squirrels in our local mountains and campgrounds.
  • Warnings will be posted by park rangers or health officials in areas where plague is found. Use caution when entering these areas.
  • Flea powder put into rodent burrows may be used to control fleas carrying plague. The powder gets in the rodents' fur after they enter, killing fleas inside the burrow. This is very effective and does not harm rodents.


  (858) 694-2888


Flea by Andrei Savitsky
Plague symptoms by Mikael Häggström