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.