Sacramento-Yolo Counties Lyme Disease Surveillance 2004

Annual Report 2004, Sacramento-Yolo Mosquito and Vector Control District

Summary of Sacramento-Yolo MVCD 2003-2004 Tick Surveillance

Location          Total   Pools    Positive   Estimated Minimum
                  Ticks   Tested   Pools (b)  Infection Rate (a)
Yolo
Cache Creek        368      42         5              1.4%
Sacramento
Ancil Hoffman        0       0         0              N/A
Mississippi Bar     83      11         1              1.2%
Negro Bar          189      22         0              0.0%
Nimbus Dam          74      11         2              2.7%
Snipes Park         64      11         0              0.0%
Willow Creek        69      12         0              0.0%
Totals             847     109         3

a IFA-positive samples were tested by a PCR assay targeting the 5S(rrf)-23S(rrl) intergenic spacer region of B. burgdorferi.
b Minimum infection rate (%) = (#positive pools/#ticks tested) x (100). Assume a positive pool contains a minimum of one infected tick.

The bacterium that causes Lyme disease is called Borrelia burgdorferi. The primary vector for Lyme disease for Sacramento and Yolo Counties is Ixodes pacificus, also known as the western black-legged tick. The table (above) summarizes the Lyme disease surveillance data from Ixodes pacificus ticks collected from November 2003 through May 2004.

Tick specimens were collected by dragging a flannel sheet along the side of a trail, a technique called flagging. The ticks were pooled and tested by indirect immunofluorescence assay (IFA). A sample was considered positive by IFA if one or more fluorescently stained spiral-shaped bacteria were present. Some positive samples were confirmed using a polymerase chain reaction assay and by culture in liquid media.

Ticks and Tick-Borne Diseases in Napa County

Source: Tick-Borne Diseases, Napa County Mosquito Abatement District

Lyme disease is present in Napa County. There were three diagnosed cases in 2001.

Rocky Mountain Spotted Fever is present in Napa County. There was one case reported by the California Department of Health Services in 2000.

The tick vector for Tularemia is present in Napa County. No known diagnosed cases have been reported.

Source: Summary of Napa County Ticks, Napa County Mosquito Abatement District

Napa County has 10 confirmed species of ticks, including the following which are vectors of Lyme Disease, Q Fever, Rocky Mountain Spotted Fever, Tularemia, and Tick Paralysis to humans.

Ixodes pacificus
Western Black-legged Tick
Widespread Californian Tick. Life cycle can be completed in less than one year but usually lasts about two years. Females lay eggs in the spring on the undersides of brush and dried leaves. Eggs hatch during early summer. Nymphs and adults seek hosts (quest) from the tips of vegetation while larval ticks find hosts close to the ground. Most commonly encountered Ixodes tick in California. Adults occur year-round but are most commonly found November through May. Nymphs are most commonly found March through June but can be found year-round. Immature stages commonly found on Alligator Lizards, Fence Lizards, and ground inhabiting birds. Sometimes found on small rodents and rabbits. Large mammals are also important hosts for larvae and nymphs. Adults are common on deer and other large mammals (dogs, bears, cats, horses, humans, etc.).
Vector of Lyme Disease. Has caused tick paralysis in a dog.

Dermacentor occidentalis
Pacific Coast Tick
Common, widespread Californian tick. Adults are found year-round with peak activity in April and May. Nymphs are most common during spring and summer. Adult hosts tend to be cattle, horses, deer and humans. Rare on dogs and bears. Nymphs tend to feed on rodents and other small mammals.
Capable of transmitting many diseases. Vector of bovine anaplasmosis. Has been found naturally infected with Colorado Tick Fever virus, the Rickettsia of Q Fever and the bacterium that causes Tularemia. Known to cause tick paralysis in cattle, horses and deer. Spotted fever group Rickettsiae have been found in ticks collected from Mendocino County. Bite wounds are commonly mistaken for wounds caused by biting insects and spiders.

Dermacentor variabilis
American Dog Tick
Widespread Californian tick. Life cycle can be completed in less than one year or take longer than two years if suitable hosts are not available. Adults are present year-round while nymphs and larvae are most active late winter to summer. Adult females may take up to 13 days to complete feeding on a host and can produce as many as 6500 eggs during their lifetime. Immature ticks are capable of surviving extreme winter temperatures. Dogs are the preferred host although adults will feed on humans and many other species of large wild and domesticated mammals. Larvae and nymphs tend to feed on rodents and rabbits.
Important vector of Rocky Mountain Spotted Fever, especially in the Eastern United States. Vector of Tularemia to humans. Known to cause tick paralysis.

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.