Lyme Disease


Lyme disease is caused by a bacterium and spread when an infected tick attaches and feeds on a human or animal. Although Lyme disease is reported across the U.S. and in most counties in California, it is rare in San Diego County.

In California, Lyme disease is spread by the bite of the Western blacklegged tick, which is mostly found in the coastal regions and along the western slope of the Sierra Nevada mountain range. The adult female is reddish-brown with black legs, about 1/8-inch-long while males are smaller and brownish-black. In San Diego County, these ticks are more prevalent during the rainy season, October – April.  

The Vector Control Program routinely collects, identifies, and tests ticks for Lyme disease and other tick-borne pathogens. If tests come back positive, warning signs are posted in the area to inform the public on how to avoid ticks and protect themselves and their pets from this serious disease.

Ticks in the larval, nymph, and adult stages attach to hosts to take a blood meal. If the host is already infected with Lyme disease from a previous tick bite, the tick will likely become infected as well. When the tick attaches to its next host, the tick can transmit the disease to the new host. Tick-to-human transmission of Lyme disease occurs only after several hours of feeding.

bull's eye rash on light skin


A small bump or redness at the site of a tick bite that occurs immediately and resembles a mosquito bite is common. This irritation generally goes away in 1-2 days and is not a sign of Lyme disease.

Early signs and symptoms (3 to 30 days after tick bite)

  • Bull's Eye Rash (see image at right - common in most but not all cases, may appear differently on darker skin tones)
  • Flu-like symptoms
  • Aching joints

Later Signs and Symptoms (days to months after tick bite)

  • Severe headaches and neck stiffness
  • Facial palsy (loss of muscle tone or droop on one or both sides of the face)
  • Arthritis with severe joint pain and swelling
  • Intermittent pain in tendons, muscles, joints, and bones
  • Heart palpitations or an irregular heartbeat 
  • Episodes of dizziness or shortness of breath
  • Shooting pains, numbness, or tingling in the hands or feet


Lyme disease is rarely fatal. If the disease is found early enough, treatment with antibiotics can cure the infection and prevent further problems. In the late stages of Lyme disease, symptoms should improve from use of antibiotics, but effects may persist in the human body for years and may never go away completely. 

Lyme disease has been diagnosed in dogs, cats, horses, goats, cattle, and several wild animals. While some animals may display no symptoms, others may develop fever, loss of appetite, painful joints, fatigue, and vomiting. If left untreated, the disease can damage the eyes, heart, kidneys, and nervous system. Check your pets for ticks and consult your veterinarian if you think they may have been infected.


These personal protection measures will help lower exposure to ticks that could be infected with Lyme disease:

  • Stay on paths and trails
    • Ticks are found in grassy, brushy areas and on the plants that line trails
    • Keep pets on leash and on trail while hiking
    • Don't feed or touch wild animals
  • Dress protectively when outdoors
    • Wear long-sleeved shirts and long pants
    • Wear light-colored clothing that shows ticks crawling on you
  • Use insect repellent
    • Use repellents containing DEET or Picaridin
    • Apply repellent to clothing and exposed skin; follow the directions carefully
  • Check yourself for ticks    
    • After you are in a tick-infested area, examine yourself and your companions for ticks and remove them right away
    • Tick nymphs may be very small, about the size of a poppy seed


  (858) 694-2888

Tick photo by Kaldari
Tick life cycle image by CDPH
Symptom photo by CDC/ James Gathany