Ticks and Lyme Disease in Contra Costa County 2006

2006 Annual Report, Contra Costa County Mosquito and Vector Control District

Lyme disease is a bacterial infection transmitted by the Western black-legged tick (Ixodes pacificus), also known as the deer tick. While Lyme disease is rare in Contra Costa County (on average there are two to four human cases reported per year), it can cause serious complications if not treated promptly. The District monitors the risk of Lyme disease by collecting and testing black-legged ticks from several locations that we have been monitoring for as long as 12 years. These include Bollinger Canyon Rd., San Ramon; Springhill Rd., Lafayette; and the Bear Creek area of Briones Regional Park. The adult Western black-legged tick population was below average for most of the season, except during the last half of March where counts slightly exceeded the average. An unusually high number of days with rainfall during the collecting season limited the number of possible collection days; thus reducing the numbers of ticks collected. The graph below shows the average number of ticks that were collected from these locations.

On average, only one or two in a hundred black-legged ticks test positive for Lyme disease, although we have found a few locations where the rate is higher, and these tend to change over time. In 2006, we collected and tested 132 ticks from three locations; the highest infection rate was in the Bollinger Canyon area in San Ramon where three out of 58 ticks tested positive (just over 5 percent).

We also identify and test ticks brought in by members of the public who have been bitten. If the ticks are reasonably intact and not dried out, we can test them in our own laboratory free of charge. If they are in poor condition or dead, a more sensitive test is required and county residents have the option of allowing us to send the tick to a private laboratory for a fee of $60 (our cost). Out of 54 ticks tested for residents in 2006, only one was positive for Lyme bacteria (just below 2 percent).

Reported Cases of Tularemia in California 2004

Annual Report 2005, Alameda County Vector Control Services

Tularemia, a diseased caused by strains of Francisella tularensis, is not commonly transmitted by contacting rodents or tick bites. However, three human cases of tularemia were reported to CDHS in 2004; two of which were likely acquired through a tick bite: one from Alameda County and one from Contra Costa County. The adult American dog tick (Dermacentor variabilis) removed from the Alameda case was tested positive by culture and PCR for F. tularensis (type B) by Center for Disease Control and Prevention (CDC). Because of the human cases and also its importance as a bioterrorism agent, the CDHS requested blood samples from various animals for testing. Blood samples from twenty-three rodents from various locations in Alameda County were submitted for testing. None of these samples showed infection with F. tularensis. United State Department of Agriculture (USDA) – Animal and Plant Health Inspection Service (APHIS) submitted additional twenty-eight blood samples of feral cats, skunks, Norway rats, jackrabbits and red foxes. Of these, one striped skunk tested positive for the tularemia pathogen.

Ticks and Lyme Disease in Contra Costa County 2005

2005 Annual Report, Contra Costa County Mosquito And Vector Control District

Tick Testing

Bollinger Canyon Rd, San Ramon Site
A total of 670 adult Western black-legged ticks were collected from the Bollinger Canyon Road site 1A this season. Seventy four ticks were tested (45 females, 29 males) for the presence of Lyme disease, using an Indirect Fluorescent Antibody test (IFA). Two of the seventy-four ticks tested were found to be positive for the Lyme disease, yielding a 2.7 percent infection rate. This is the twelfth season for which ticks have been tested from this site. The average infection rate over the twelve year period is 3.71 percent, which is slightly higher than the Californian State average of 2.0 percent. The chart below shows the Lyme disease (B. burgdoferi) infection rate at the Bollinger Canyon Site between the 1993-94 to 2004-05 seasons.

Springhill Rd, Lafayette Sites
In addition to our regular Lyme disease IFA testing, a total of 374 adult Western black-legged ticks were collected from five sites near Springhill Road, Lafayette, and were tested using real-time PCR by Dr. Alan Barbour of University of California, Irvine, for the presence of two species of Lyme disease causing bacterium, Borrelia burgdorferi and Borrelia miyamotoi. Borrelia miyamotoi is closely related to B. burgdoferi, but at this time has not been shown to cause disease in humans. This location was chosen as it was an area previously known to have had high Lyme disease infection rates in Western black-legged ticks that were collected by both Contra Costa Mosquito & Vector Control staff and those submitted by the public to our office for testing. The infection rates have varied yearly from 0-14 percent.

Ticks and Lyme Disease in Contra Costa County 2004

2004 Annual Report, Contra Costa County Mosquito and Vector Control District

Due to a temporary reduction in our laboratory staff this summer, Lyme disease testing of ticks collected during the 2003/04 field surveillance season is not yet complete.

There were a total of 124 ticks submitted for identification by the public during 2004. Forty-five were identified as the western black-legged tick (the potential vector of Lyme disease). Of these, 11 were tested in-house using the IFA method (one positive) and 28 were submitted to IgeneX Labs for PCR testing (results no longer being reported to the district).

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).

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.