San Mateo County: Lyme Disease Surveillance

Entomology Report October 2005, San Mateo County Mosquito Abatement District

Surveillance for the western black-legged ticks (Ixodes pacificus) will commence in November. This tick is a vector of the Lyme disease spirochete, Borrelia burgdorferi. Adults of this species feed on large mammals such as deer, humans, horses and dogs. They are the primary tick found along recreational trails from November through May. Surveys in past years have detected Lyme disease spirochetes in 2% of adult and nymphal ticks in San Mateo County. The prevalence of infection has not differed significantly between years, sites or life history stage of ticks.

Laboratory staff will test ticks submitted by residents free of charge and provide information on Lyme disease and ways to minimize exposure to it.

This year, the district hopes to expand the surveillance program to include more parks, and estimate relative public health risk at different recreational sites based on degree of public use, tick density, and prevalence of infection in ticks.

Protect Yourself

People who frequent high risk areas can protect themselves from ticks by tucking their pants into their socks and thoroughly checking skin, hair, clothing and pets for ticks before returning home. Light colored clothing helps make ticks more visible so that they can be removed before attaching. Permethrin can be applied to the outside of your clothes to repel ticks. Products labeled for use on clothing can be obtained at stores that sell recreational equipment. Always read and follow the directions on the label of any pesticide before using it. Permethrin should never applied directly to bare skin.

Removal of ticks: With tweezers, firmly grasp the tick as close to the skin as possible and pull tick straight up and out.

Symptoms of Lyme Disease: Fatigue, chills, fever, headache, muscle and joint aches, swollen lymph nodes, and other neurological symptoms. This disease is caused by a bacteria and therefore can be treated with antibiotics.

Previous related entries:

San Mateo County: Lyme Disease Surveillance, January 2005

Tick-Borne Disease Surveillance in California, 2004

Vector-Borne Diseases in California, Annual Report 2004, California Department of Health Services, Vector-Borne Disease Section

Human disease surveillance

Lyme disease

Fifty-two cases of Lyme disease were reported to the California Department of Health Services (CDHS) in 2004. Case-patients were residents of 24 counties. Humboldt County reported the most cases (8) and incidence was highest in Trinity County at 23 cases per 100,000 residents. Of 32 cases for whom site of likely exposure was reported, 12 (37.5%) had exposure outside of their county of residence; 7 (22%) of these reported exposure outside California. The most frequently reported location of exposure was Humboldt County (9 cases).

The median age of reported Lyme disease cases was 32 years (range, 3 to 80 years) and 31 (60%) were male. Race was reported as white for 47 (91%) cases, Asian for 3, black for 1, and unknown for 1 case. Erythema migrans (EM) was identified in 23 (44%) cases. Of 22 cases with EM for which date of illness onset was reported, 13 (59%) occurred between May and August.

Anaplasmosis

Two cases of human granulocytic anaplasmosis (HGA, formerly known as human granulocytic ehrlichiosis) were reported to CDHS in 2004. In June, a 53-year-old female resident of Alameda County developed high fever (104 degrees F), headache, malaise, and rash. The CDHS Viral and Rickettsial Disease Laboratory (VRDL) detected antibodies to Anaplasma phagocytophilum (IgM > 1:40, IgG > 1:1024) in a serum specimen collected approximately four weeks after onset. The patient recovered without specific treatment.

The patient reported removing an attached tick from her back at least 12 hours after hiking in Tilden Park, Alameda County. In July 2004, CDHS staff conducted surveillance for ticks at Tilden Park. One Ixodes pacificus adult female tick was recovered and tested negative by polymerase chain reaction (PCR) to A. phagocytophilum at the United States Army Center for Health Promotion and Preventive Medicine - West at Fort Lewis Washington (USACHPPM). Although A. phagocytophilum were detected by PCR in I. pacificus collected from Alameda County in 1996, this was the first HGA case reported from this county.

A second case of anaplasmosis was reported in a male resident of San Mateo County. The case-patient had onset of illness in December following a tick bite he received in New Jersey.

Rocky Mountain Spotted Fever

One case of Rocky Mountain Spotted Fever (RMSF) was reported to CDHS in 2004. In June, a 52-year-old male resident of San Mateo County presented to an emergency room with fever (101 degrees F - 104 degrees F), lethargy, altered consciousness, and hallucinations. The patient was hospitalized and three days later developed a macular rash that began on the palms and soles and expanded to the upper limbs and trunk. Despite initiation of antibiotic treatment, the patient remained comatose with encephalitis for four days. The patient eventually improved and was discharged from the hospital 13 days after admission. The VRDL detected a significant rise in IgG titer to Rickettsia rickettsii between acute (1:4096) and convalescent (1:16,384) sera collected approximately seven and seventeen days after onset, respectively. The patient reported travel and camping in Marin and San Mateo Counties in May and June; he had observed ticks but did not recall a specific bite. Staff of Marin-Sonoma Mosquito and Vector Control District and the CDHS Vector-Borne Disease Section (VBDS) collected three male and one female Dermacentor occidentalis ticks from the Marin County site in July. VBDS and staff from the San Mateo County Mosquito Abatement District collected four male and two female D. occidentalis, three male, six female, and one nymphal D. variabilis, and one female and five nymphal I. pacificus from two sites in San Mateo County in July. The USACHPPM reported detecting by PCR Spotted Fever Group Rickettsia in two D. occidentalis from Marin County and one D. variabilis from San Mateo County.

Tularemia

Three cases of tularemia were reported to CDHS in 2004, two of which were likely acquired through a tick bite. In late May, a ten-year-old male resident of Contra Costa County developed cervical lymphadenitis. He was initially treated as an outpatient but did not improve. The CDHS Microbial Disease Laboratory (MDL) cultured Francisella tularensis (Type A) from a lymph node aspirate obtained approximately five weeks after onset. In late June, a five-year-old male resident of Alameda County had similar onset of fever and cevical lymphadenitis. The MDL isolated F. tularensis (Type B) from a lymph node culture in July from the Alameda patient. Both patients recovered following short hospitalizations.

The Alameda case-patient had camped in San Mateo County about five days prior to oneset and had visited Tilden Park in Alameda County about 10 days earlier. The Contra Costa case-patient also walked trails in Tilden Park in the week prior to onset. Neither patient had any contact with rabbits or other wild animals. Both case-patients reported tick bites to their face or head about three days prior to onset of illness. The tick from the Alameda case was retained and later identified by CDHS staff as an adult D. variabilis.

In July, CDHS conducted surveillance for ticks at the Tilden Park and San Mateo locations. Forty D. occidentalis were collected from Tilden Park and 16 D. occidentalis and 87 D. variabilis from the San Mateo location. Ticks were submitted to the Division of Vector-Borne Infectious Diseases, U.S. Centers for Disease Control and Prevention, for culture and PCR. F. tularensis (Type B) was identified in the tick recovered from the Alameda patient; all ticks collected in the field were negative.

Tick-borne relapsing fever

Six cases of tick-borne relapsing fever were reported to CDHS in 2004. Case-patients were residents of five counties (Contra Costa, El Dorado, Madera, San Mateo, and Santa Clara) and ranged from 8 to 49-years-old. Five case-patients were likely infected while visiting the western Sierra Nevada; exposure information was unavailable for one case.

Sacramento-Yolo Counties Lyme Disease Surveillance 2005

Annual Report 2005, Sacramento-Yolo Mosquito and Vector Control District

Summary of Sacramento-Yolo MVCD 2004—2005 Tick Surveillance Data

Location          Total   Pools    Positive   Estimated Minimum
                  Ticks   Tested   Pools      Infection Rate
Yolo
Cache Creek        257      23         3              1.2%
Sacramento
Ancil Hoffman        0       0         0              N/A
Mississippi Bar     66      12         1              1.5%
Negro Bar           19      13         0              0.0%
Nimbus Dam          38       9         2              2.7%
Snipes Park         68      13         0              0.0%
Willow Creek        46      10         0              0.0%
Total              494      80         8

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... summarizes the Lyme disease surveillance data of Ixodes pacificus ticks collected from November 2004 through May 2005.

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.