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.

Alameda County Lyme Disease Surveillance, 2001-2002

Annual Report 2001-2002, Alameda County Vector Control Services

As part of the Lyme disease surveillance program, District Staff identify ticks and mites, and will authorize testing for tick borne disease when appropriate. The District is currently investigating two human Lyme disease, case histories, from victims who are believed to have acquired the disease in Alameda County. The collections and surveillance will occur in the spring of 2002, when the adult and nymphal Ixodes pacificus ticks are most numerous. As part of the general tick borne disease surveillance program, 49 Western Black Legged Ticks were tested and none were positive for Borrelia burgdorferi. Vector control officers are being trained in tick surveillance techniques and equipment, and plans are in place to increase tick surveillance. Sixty-Five residents of Alameda County were bitten by ticks, and submitted them to the Alameda County Public Health Laboratory for Lyme disease testing. Some additional samples were sent to IgeneX, a private laboratory for PCR Testing. All of the twenty-four ticks acquired in Alameda County tested negative for the Lyme disease spirochete. Additional ticks, one from France and another from the east coast, tested positive for Borrelia burgdorferi, the bacteria responsible for Lyme disease.