Ticks and Lyme Disease in Contra Costa County 2003

2003 Annual Report, Contra Costa County Mosquito and Vector Control District

CCMVCD Adult Ixodes pacificus Surveillance Summary
Location                           # tested  # pos.  % Infected
Bollinger Cyn. Rd, San Ramon            100      2      2%
Briones RP, Bear Creek Staging           76      0      0%
Springhill Rd (End), Lafayette          100      1      1%
Springhill Rd (middle), Lafayette        46      4      9%
Springhill Rd (middle), Lafayette         7      1     14%
Springhill Ln, Lafayette                 70      8     11%
Leslyn Ln, Lafayette                     28      1      4%
Brown Rd, Lafayette                      17      0      0%
Shire Oaks Ct., Lafayette                96      0      0%
Joseph Dr., Orinda                       56      0      0%
Grover Ln., Walnut Creek                 54      0      0%
Contra Costa County 2002-03 season      650     17      3%

Bollinger Canyon Rd, San Ramon Site
A total of 500 adult I. pacificus were collected from the Bollinger Canyon Rd. site this season. One hundred individuals were tested (39 females, 61 males) for the presence of B. burgdorferi and two were found to be positive. This is the tenth season for which ticks have been tested from this site and the average infection rate over that ten year period is 3.75%.

Bear Creek Area, Briones Regional Park
There were 106 ticks collected from the Bear Creek area of Briones Regional Park this season. Seventy two of these were tested and none were found positive. This was a little surprising given that during the 2001-02 season the infection rate was five percent. It has been noticed in the past however, that infection rates are not necessarily stable. For instance, the infection rate at the Bollinger Canyon site has ranged from 0-9% over a ten year period.

Springhill Rd, Lafayette Sites
During the 2001-02 season a second location was found on Springhill Rd. where infected I. pacificus were present. This season we returned to Springhill Rd. and collected ticks from five locations including the original one where 13 percent of the ticks collected previously were positive for B. burgdorferi. Infected ticks were found at all sites except for one and the infection rate ranged from 0-14 percent. The specific results are summarized along with all others in the table (above).

Alameda County Lyme Disease Surveillance, 2002-2003

Annual Report FY 2002-2003, Alameda County Vector Control Services

As part of the Lyme disease surveillance program, staff collect and identify ticks, and may recommend testing for tick borne disease when appropriate. Seventeen field surveys were conducted at nine locations, which resulted in the capture of 182 adult Ixodes pacificus ticks. Three of these ticks were confirmed to be Lyme disease positive by direct immuno-fluorescence (IFA). The three positive ticks represented about 1.6% positive for Lyme disease from the samples taken so far. This number is slightly below the two percent figure, which is the typical average for endemic Lyme disease areas in California. Alameda County continues to have a low incidence of locally acquired Lyme disease, mainly due to its’ isolated number of suitable habitats for the reservoir and vector.

Twenty-seven residents of Alameda County were bitten by ticks, and submitted them to the Sonoma County Public Health Laboratory for Lyme disease testing. All of the twenty-seven ticks acquired in Alameda County tested negative for the Lyme disease spirochete. Two Lyme disease case histories from the previous year were completed in 2002. The areas where these victims had frequented were surveyed several times, but none of the tick samples yielded positive results for the Lyme disease spirochete, Borrelia burgdorferi.

Ticks and Lyme Disease in Contra Costa County 2002

2002 Annual Report, Contra Costa County Mosquito and Vector Control District

Adult Ixodes pacificus Surveillance Summary
Location                            # tested  # pos.  % Infected
Bollinger Cyn. Rd, San Ramon             100      1      1%
Springhill Rd (End), Lafayette           100      1      1%
Briones RP, Bear Creek Staging            40      2      5%
Springhill Rd. (middle), Lafayette        24      3     13%
Donald Rheem Elementary, Moraga           13      0      0%
Brookside Rd., Orinda                      8      0      0%
Alameda Diablo, Diablo                    54      0      0%
Contra Costa County 2001-02 season       339      7      2%

IFA Testing Results

During the 2001-02 tick season, adult I. pacificus (Western Black-legged tick) that were collected from Bollinger Canyon Rd., San Ramon; Springhill Rd. in Lafayette; and at the Bear Creek Staging area of Briones Regional Park were tested for the presence of the Lyme disease spirochete, Borrelia burgdorferi. Ticks were also collected and tested from other miscellaneous locations within the County in order to continue to expand on the current picture of the average Borrelia burgdorferi infection rate in Contra Costa County. Details are summarized below.

Springhill Rd, Lafayette Site
A total of 204 adult I. pacificus were collected from the Springhill Rd. site during the 2001-02 season, 36 percent females and 64 percent males. One hundred individuals were tested (40 females, 60 males) for the presence of Borrelia burgdorferi and a single tick was found positive. The infection rate at this location has been as high as six percent with an average infection rate of 1.38 percent over the nine year period that we have been collecting data from this site.

Bollinger Canyon Rd, San Ramon Site
Five hundred thirty-seven I. pacificus adults were collected from the Bollinger Canyon Rd. site, 47 percent females and 53 percent males. One hundred ticks were tested and one was found positive for B. burgdorferi. This site has had a history of higher-than-average infection rates. Over the last five years however, infection rates have been in the 0-2 percent range. The average infection rate for this location over the last nine years is 3.28 percent.

Briones Regional Park Site
The Briones Regional Park site typically has a low I. pacificus population. During the 2001-02 season only 53 individuals were collected, 40 of which were tested. The table (above) is a summary of all sites surveyed this season and includes four additional locations within the County where ticks were collected and tested for B. burgdorferi infection. Also included are the overall totals and average infection rate for Contra Costa County.