Lyme Disease

Overview & History: 

Lyme disease is caused by an infection with the bacterium Borrelia burgdorferi. In California, the bacterium is transmitted by the bite of an infected western black-legged tick (Ixodes pacificus). Wild rodents and other small animals are the natural reservoir hosts of the disease. Although deer are not reservoirs of the disease, high deer populations contribute to elevated tick populations, thus potentially increasing the prevalence of the disease.

In the United States, Lyme disease is most prevalent in the northeastern states, but cases are commonly reported in many other areas, including California. Worldwide, reported cases of Lyme disease are concentrated in northern and central Europe. 

Impact on human health: 
  • Lyme disease may produce a wide range of symptoms. If you believe that you have been exposed to the bacterium that causes Lyme disease, contact your health care provider. 
  • Some people infected with Lyme disease develop a circular rash called erythema migrans (or "bull's eye" rash) within 3-30 days of being bitten by an infected tick. 
  • If Lyme disease is left untreated, the infection may spread to other parts of the body, with many patients experiencing severe pain and swelling associated with arthritis.Untreated patients may also develop chronic neurological problems.
  • Click here for more information regarding signs and symptoms of Lyme disease.
  • Antibiotics are most effective when treatment is started early.
  • A Lyme disease vaccine is currently not available for humans.
What you can do to protect yourself: 

Before entering tick habitat, take the following precautions:

  • Consider applying an effective tick repellent to exposed skin. Click here to use the EPA's repellent search tool.
  • Consider treating clothes/personal outdoor equipment with an acaricide containing permethrin.
  • Wear light-colored clothing (this makes it easier to spot ticks).
  • Wear long pants, long sleeves, and long socks whenever possible (this makes it more difficult for the tick to get to your skin).

While in tick habitat:

  • Stay on trails (adult ticks are typically more abundant on the uphill sides of trails).
  • Avoid contact with nymph habitat (leaf litter, logs, tree trunks, etc.).
  • Periodically check for ticks on people and animals.

After exiting tick habitat:

  • Wash all clothes in hot water and dry on high heat.
  • Shower after coming indoors and carefully check for ticks.
  • Properly remove any attached ticks immediately (please see our tick brochure for proper removal technique).

Reduce tick abundance around the home:

  • Utilize landscaping techniques that limit cover for ticks near the home, such as removing leaf litter around homes and using gravel or woodchip barriers between lawns and wooded areas (see the Tick Management Handbook for detailed information). 
  • If properly timed, application of acaricides (pesticides designed to kill ticks) can be effective in reducing tick populations near homes. Residents should contact a private pest control company if they are interested in this service.
Impact on animals/wildlife: 
  • Dogs may become infected with the bacterium that causes Lyme disease and may exhibit a wide variety of symptoms. Pet owners should consult their veterinarian if they are concerned their dog has been exposed to the bacterium that causes Lyme disease. 
  • In California, cats are typically bitten less frequently than dogs by the western black-legged ticks. 
  • Infected western black-legged ticks commonly feed on western fence lizards, but the lizard blood kills the Borrelia bacterium.