San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide



Lyme Disease

The Natural History of Disease

Lyme Disease

Lyme disease is a serious infection caused by the bacteria Borrelia burgdorferi, and transmitted by the western black-legged tick (Ixodes pacificus). The tick may also carry other diseases that can be transmitted along with the Lyme bacteria: Colorado tick fever, human grannulocytic ehrlichiosis, human monocytic ehrlichiosis, Rocky Mountain Spotted fever (one confirmed case in California 2000), tularemia, relapsing fever, tick paralysis, and babesiosis. Infection offers no immunity and a person can be infected more than once. Currently there is no consensus on how to diagnose the disease and there is intense debate in the medical and insurance community about diagnosis and length of treatment. Without proper and early treatment it can become a chronic illness with persisting infection. Lyme disease is diagnosed clinically, and once detected it is recommended that individuals be treated with antibiotics immediately and until all the symptoms are gone.

Risk Groups

High-risk groups include foresters, farmers, ranchers, field biologists, trail builders, trail users, rangers, gardeners, hunters, joggers, and vacationers. Though more common in the northeastern, mid-Atlantic, and upper north-central regions of the United States, Lyme disease is also found in California, especially in northwestern counties. As of October 31, 2000, 95 cases of Lyme disease were reported to the California Department of Health Services. Ticks have been collected and tested positive for Lyme disease at Will Rogers State Historic Park and Charmlee Park, both in Los Angeles. According to some doctors, this disease is greatly under diagnosed and under reported. A small number of cases are reported in San Diego every year.

photos of four deer ticks: adult to larvae, courtesy of CDC
Deer tick (Ixodes scapulari), adult male, adult female, nymph, and larva on a centimeter scale. The western black-legged tick (Ixodes pacificus), similar in size, transmits the bacteria on the Pacific Coast. Photo courtesy of Centers for Disease Control.


Nymphal ticks are the more serious transmitters, with infection rates many times that of the adult tick. The nymphs are about the size of a poppy seed, readily attach to humans, and feed about twice as fast as the adults. They are most commonly found from March to July in moist leaf litter in oak woodland, mixed chaparral, madrone forest, and redwood forests. Nymphs feed on mice, lizards, birds, rabbits, raccoons, deer, cows, horses, dogs, cats, and humans. Wood rats (pack rats) have been found to be a reservoir for the disease in the coastal region. Migrating birds spread Lyme disease. The bird will eat on the ground where a tick can attach. The bird can then fly in any direction spreading the disease. The western fence lizard has an unknown component

Adult ticks are active from October to June and peak in December, January, and February (depending on the area). They "quest" on low vegetation and grasses, approximately 24 inches tall, waiting for a host meal to pass. The majority are found in shaded moist ecotones (where two vegetation types come together, in this case grass and shrubs) on the north-facing uphill side of a trail. The females are more likely to transmit the disease since they need a large blood meal to develop eggs.

Symptoms: a flat or slightly raised red lesion (erythema migrans) at the site of the tick bite, expansion of the red lesion to several inches over several days, fever, headache, lethargy, muscle pains, stiff neck, joint inflammation in the knees and other large joints. Additional symptoms could include itching overall and unusual or strange behavior.

Tests: Physical examination and blood test for antibodies to B. burgdorferi by immunofluorescence (IFA) or ELISA.


  • Dress appropriately. Wearing shorts into tick habitat increases the risk. Tuck pants into boots, and shirt into pants. Pull socks over pants. Wear a hat.
  • Wear light colored clothing so ticks can be easily seen.
  • Apply Permanone (0.5% Permethrin) on clothing to repel or kill ticks. Apply insect repellents containing 25% or less of DEET on exposed skin of adults and 10% on children. Use pesticides in a responsible manner.
  • Stay in the middle of a trail and avoid trail margins, brush, and grassy areas, when in tick habitat.
  • Conduct tick checks on yourself and your children frequently.

Environmental safeguards

  • Mow grass along trails, buildings, and camping areas.
  • Remove brush along trails or other areas of high human activity.
  • Check your pets for ticks.
  • Recognize tick habitat: shaded moist ecotones on the uphill side of a trail, where animals bed down or make nests, and moist leaf litter in oak woodland and mixed chaparral.
  • Spraying area application of insecticides in yard, around property is questionable.


  • Educate yourself about Lyme disease and other tick-borne illnesses
  • Protect yourself if you're going to be in tick habitat.
  • If you find an attached tick on your body, have it removed properly. (See below)
  • Record any symptoms or changes you may have daily.
  • Photograph the "bull's eye" rash if you have one. It will disappear with or without antibiotics.
  • Seek Lyme-literate doctors.

Tick removal device:
Pro-tick Remedy
$3.50 each
SCS Limited
P.O. Box 573
Stony Point, NY 10980
(800) 749-8425

Lyme tests and testing for dead ticks:
IgeneX, Inc. reference laboratory
797 San Antonio Road
Palo Alto, CA 94303
(800) 832-3200
(415) 424-1191
FAX (415) 424-1196

Removal of an embedded tick

  • Do not twist tick or cover it with vaseline.
  • The sooner you remove the tick the less chance of infection. Use either a tick removing device or a fine-point tweezers. Do not squeeze the tick body or hold a cigarette, or match to it (you could inject the possibly infected body contents into the wound). Grasp it as close to the skin as possible, where the mouth parts enter the skin. Tug gently and repeatedly until it releases its hold by withdrawing its barbed mouth parts from your skin. Above all, be patient, as proper tick removal will take time. Don't squash the tick with your hands.
  • To have a tick tested to see if it is infected, put the live tick into a clean pill bottle or camera film container with a piece of dampened cotton for moisture and contact the Department of Environmental Health or send it to a reliable laboratory.
Inform yourself

Lyme Disease: Introduction (Centers for Disease Control)
Lyme Disease Foundation
Lyme Disease Resource Center
Six Tick Removal Tips ( Medical Encyclopedia)
Western Black Legged Tick (San Diego County Department of Environmental Health)

Thanks to Virginia Moran for sharing materials on Lyme disease obtained at the 2001 Annual Meeting of the Western Section of the The Wildlife Society.

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