The California Department of Public Health, Vector-Borne Disease Section (CDPH-VBDS) and its partner agencies collect and test ticks for tick-borne pathogens as part of a statewide vector-borne disease surveillance program. CDPH also collects information on reported confirmed human Lyme disease cases in California.

In California, the western blacklegged tick (Ixodes pacificus) is the vector (or carrier) of Lyme disease caused by the agent Borrelia burgdorferi. This story map displays county-level summaries of blacklegged tick collections since 1985, Borrelia burgdorferi testing since 1985, and the number of reported confirmed human Lyme disease cases by county of residence from 20010 to 2019.

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Layers:

County summaries of Ixodes pacificus collections and testing in California from 1985-2019: This layer provides county-level summaries of western blacklegged tick collections and Borrelia burgdorferi testing results from 1985 to 2019. Results for the nymphal and adult tick stages are provided. Note that nymphal ticks may pose a higher Lyme disease infection risk to humans than adult ticks.

Ixodes pacificus collection locations, 1985 - 2019: This layer shows where western blacklegged ticks have been collected throughout the state.

County Ixodes pacificus collection totals, 1985 - 2019: This layers provides a county-level summary of the total number of Ixodes pacificus collected from 1985 - 2018.

Lyme Disease Incidence, 2010 - 2019: This layer presents the number of confirmed human Lyme disease cases per 100,000 person-years by county. Click on a county to view the incidence for that county.

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Notes:

• Since tick collection is not done uniformly throughout the state, absence of tick collection or Borrelia burgdorferi-positive ticks in a given area may indicate lack of surveillance data; it does not mean that ticks or infected ticks are absent.
• Data on this map represent ticks collected by the California Department of Public Health, local mosquito and vector control agencies, and other public agencies. Data for ticks independently tested by local mosquito and vector control agencies may not be included on this map.

The map shows how many people after a tick bite with a red spot or ring on the skin were seen by the doctor in 2017. This is a first symptom of Lyme disease. In the red areas, most cases have been reported.

The map shows how many people were seen by the GP after a tick bite with a red spot or ring on the skin in 2017. This is a first symptom of Lyme disease. Most cases have been reported in the red areas.