Tick Surveillance in California, 2005

Vector-Borne Diseases in California, Annual Report 2005, California Department of Health Services, Vector-Borne Disease Section

Tick surveillance

CDHS Vector-Borne Disease Section (VBDS) and collaborating agencies conducted tick surveillance in 17 California counties in 2005. Totals of 1,965 Ixodes pacificus (1,797 adults and 168 nymphs), 782 Dermacentor occidentalis, and 38 Dermacentor variabilis were collected. Nineteen hundred I. pacificus (1,736 adults and 164 nymphs) from 16 counties were tested for Borrelia burgdorferi in two laboratories. Ticks were tested by indirect fluorescent antibody (IFA) and/or polymerase chain reaction (PCR). Evidence of Borrelia sp. was identified in ticks collected from six counties. Borrelia burgdorferi was detected in 4 of 33 pools by IFA and 12 of 192 pools by PCR.

The U.S. Army Center for Health Promotion and Preventive Medicine tested by PCR 1,618 I. pacificus. Any ticks initially positive for the genus Borrelia were tested by an additional PCR assay using primers specific to B. burgdorferi. Borrelia sp. spirochetes detected in tick pools from Placer (1), Shasta (1), Trinity (1), Tuolumne (1) Counties did not match the genetic sequence for B. burgdorferi. These isolates most closely resembled B. miyamotoi, a Borrelia species in the RF genetic complex. Borrelia miyamotoi is not known to be pathogenic to humans.

A study of the ecology of I. pacificus in southern California, initiated in 2001, continued in 2005. VBDS and collaborating agencies (Los Angeles County Department of Health Services, Los Angeles West Vector Control District, and Riverside County Department of Health) monitored tick populations and collected questing ticks from six sites at three different geographic locales (Griffith Park, Santa Monica Mountains, and San Jacinto Mountains). Meterological factors, including rainfall and humidity, were simultaneously monitored. These data on tick populations, meterological factors, infections with B. burgdorferi, and molecular characterization of Borrelia spp. from ticks will continue to be collected to gain a better understanding of the ecology of I. pacificus ticks and B. burgdorferi in southern California.

Local surveillance was conducted in San Mateo County for Rickettsia rickettsii, the agent of Rocky Mountain spotted fever. In June, CDHS and San Mateo County Mosquito Abatement District personnel collected 320 D. occidentalis and 27 D. variabilis. All ticks were tested by PCR for R. rickettsii by CDHS, Viral and Rickettsial Disease Laboratory; all tested negative. In addition, 120 Rhipicephalus sanguineus were collected from Riverside County. Of 62 ticks tested by PCR at the Division of Viral and Rickettsial Diseases, CDC, R. rickettsii was detected in one adult male R. sanguineus.

In June, CDHS collected 362 D. occidentalis and 5 D. variabilis in Tilden Regional Park, located in Contra Costa and Alameda Counties, as part of a continuing investigation of two human cases of tularemia in 2004. Ticks were tested for Francisella tularensis in 39 pools by PCR at DVBID CDC; all pools tested negative.

Tick-Borne Disease Surveillance in California, 2005

Vector-Borne Diseases in California, Annual Report 2005, California Department of Health Services, Vector-Borne Disease Section

Human disease surveillance

Lyme disease

A total of 94 cases of Lyme disease were reported to the California Department of Health Services (CDHS) in 2005. Case-patients were residents of 26 counties. Humboldt County reported the most cases (11). Reported incidence was highest in Trinity County at 23 cases per 100,000 residents. Of 44 cases for whom county of likely exposure was reported, 32 had exposure outside their county of residence; 28 of these reported exposure outside California. The most frequently reported location of exposure was Massachusetts (eight cases).

The median age of reported Lyme disease cases was 43 years (range, 3 to 78 years) and 51 (54%) were female. Of 79 cases for which race was reported, 74 (94%) were white, 3 were Native American, and 1 each was Asian and Black. Erythema migrans (EM) was identified in 59 (63%) cases. Of 51 cases with EM for which date of illness onset was reported, 36 (71%) occurred between May and August.

Tick-borne relapsing fever

Five cases of tick-borne relapsing fever (RF) were reported to CDHS in 2005. Case-patients were residents of three counties (El Dorado, Humboldt, Santa Cruz) and ranged from 6 to 58 years old. Four case-patients were likely infected in the greater Lake Tahoe area; one case-patient was likely infected while visiting a private cabin in Lassen County. One case had onset of illness in April, while the remaining four had onset in late July and August.

CDHS collaborated with the El Dorado County Departments of Health and Environmental Management, the Nevada State Health Division, and the Division of Vector-Borne Infectious Diseases (DVBID), U.S. Centers for Disease Control and Prevention (CDC), to investigate two cases of RF with unusually severe clinical courses. A 46-year-old woman from Nevada and a 43-year-old woman from El Dorado County both developed RF between February and April that progressed to severe respiratory distress and extended hospitalizations. Both patients eventually recovered. Both case-patients had a history of travel to or residence in the Lake Tahoe area. Preliminary investigation of the California case’s residence revealed live and dead mice in the garage, as well as live chipmunks in and around the house. One engorged Ornithodoros sp. tick was discovered in the bedroom. Several Ornithodoros ticks were also recovered from rodent and bird nests removed from underneath the building’s exterior siding.

Reported Lyme Disease Cases by County of Residence, California, 1996-2005

Vector-Borne Diseases in California, Annual Report 2005, California Department of Health Services, Vector-Borne Disease Section

Reported Lyme disease cases by county of residence,
California, 1996-2005.
                                                      Incidence/
                                                      100,000
County        '96 '97 '98 '99 '00 '01 '02 '03 '04 '05 person-yrs
Alameda         2   3   6   3   4   3   5   1   0   5   0.22
Alpine          0   0   0   0   0   0   0   0   0   0   0.00
Amador          0   0   0   1   0   1   0   0   0   0   0.57
Butte           4  53  13  18   3   1   3   2   2   0   4.84
Calaveras       0   0   0   0   1   0   0   0   0   0   0.25
Colusa          0   0   0   0   0   0   0   0   0   0   0.00
Contra Costa    1   6   2   1   1   5   3   4   0   4   0.28
Del Norte       0   1   0   1   0   0   2   0   0   0   1.44
El Dorado       0   3   2   1   0   0   0   0   3   3   0.75
Fresno          1   0   0   0   1   0   0   0   0   0   0.02
Glenn           0   2   0   1   1   0   0   0   0   0   1.50
Humboldt        5  19  20  14  10   4   4   5   7  11   7.80
Imperial        0   1   0   0   0   0   0   0   0   0   0.07
Inyo            0   0   0   0   0   1   0   0   0   0   0.55
Kern            1   2   2   2   2   0   2   1   0   2   0.21
Kings           0   0   0   0   0   0   0   0   0   0   0.00
Lake            0   1   2   1   0   1   0   1   1   1   1.36
Lassen          0   2   1   2   0   0   2   0   0   0   2.04
Los Angeles     2   6   3   7   2   9   6   7   2   9   0.05
Madera          0   0   0   1   0   0   0   0   0   0   0.08
Marin           0   4   8   4   3   1   4   4   0   1   1.25
Mariposa        0   0   0   0   0   0   1   0   1   0   1.17
Mendocino       3   2  16   8   7   4  11   6   2   0   6.90
Merced          0   2   0   1   1   0   0   0   0   0   0.19
Modoc           0   0   0   0   0   0   0   0   0   0   0.00
Mono            1   0   0   1   0   0   0   3   1   0   4.67
Monterey        0   2   1   2   1   0   5   1   1   0   0.32
Napa            1   3   0   2   2   3   3   0   1   1   1.28
Nevada          2   1   4   5   9   6   3   4   1   3   4.12
Orange          0   0   1   2   3   0   3   2   0   1   0.04
Placer          0   5   4   2   1   4   3   0   2   2   0.92
Plumas          3   0   2   1   0   1   0   0   0   0   3.37
Riverside       1   0   0   0   3   2   1   2   1   4   0.09
Sacramento      0   5   1   1   3   4   1   4   2   6   0.22
San Benito      0   0   0   0   0   1   1   0   0   0   0.37
San Bernardino  0   0   0   1   1   0   0   2   0   0   0.02
San Diego       5   4   0  16   9   3   7   2   4   8   0.20
San Francisco   4   1   7   1   2   3   3   3   1   7   0.42
San Joaquin     1   2   0   0   0   0   0   0   0   0   0.05
San Luis Obispo 1   0   1   1   1   0   0   0   0   1   0.20
San Mateo       2   3   4   4   2   4   4   5   1   4   0.46
Santa Barbara   1   1   3   0   0   1   2   2   2   0   0.30
Santa Clara     2   4   6   2   2   2   6   4   0   2   0.18
Santa Cruz      2   2   2   2   5   9   1   8   3   0   1.32
Shasta          1   0   2   0   0   2   1   0   2   2   0.61
Sierra          0   0   0   0   0   0   0   0   0   0   0.00
Siskiyou        0   1   1   0   0   1   1   0   0   0   0.89
Solano          0   0   0   0   1   1   0   0   0   0   0.05
Sonoma         13  10  15  14   8   6   4   9   2   9   1.95
Stanislaus      3   1   0   0   1   1   0   0   0   1   0.16
Sutter          0   1   0   0   1   1   0   0   0   0   0.38
Tehama          0   1   1   0   2   0   0   0   0   0   0.72
Trinity         1   0   1  13   1   1   1   1   3   3  19.23
Tulare          1   0   1   1   0   2   0   2   0   0   0.19
Tuolumne        1   0   0   0   0   2   1   0   0   1   0.91
Vetura          0   0   2   1   2   2   1   1   2   1   0.16
Yolo            0   0   0   0   0   0   2   0   1   0   0.18
Yuba            0   0   1   1   0   0   0   0   0   0   0.33
Total          65 154 135 139  96  92  97  86  48  94   0.30

San Mateo County: Tularemia Detected in Coastal Ticks

Entomology Report September 2006, San Mateo County Mosquito Abatement District

Tularemia has been detected in ticks collected south of Pescadero this summer. The ticks were collected in July. Results of testing (conducted at the Centers for Disease Control) were received this month. This survey was conducted along with staff from the California Dept. of Health Services in response to a human case of tularemia. The patient had exposure to ticks in coastal San Mateo County, as well as locations in Marin and Alameda Counties. Tularemia was detected by PCR in 1 of 6 pools of Dermacentor occidentalis (totaling 43 ticks) and 1 of 17 pools of D. variabilis (211 ticks). The minimum infection rate for these ticks was 1 out of 43 or 2.8% for D. occidentalis, 1 out of 211 or 0.5% for D. variabilis and 2 out of 247 or 0.8% overall. This is somewhat lower than the prevalence of Lyme disease spirochetes in western black-legged ticks (1-3% countywide). The MIR calculated for D. occidentalis is probably not an accurate estimate for that species because the number tested was small.

Dermacentor ticks reach their peak numbers in the summer (June-July). They are found in drier areas and later in the year than the western black-legged tick which transmits Lyme disease.