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).