Saint Louis encephalitis (SLE) is a mosquito-borne disease that was historically present in California, but became very rare after the arrival of West Nile virus in 2003. However, in the last two years there have been an increasing number of detections in mosquitoes and chickens and human disease cases from southern California. Continued surveillance for this virus is important because it might be resurging.
During March, laboratory staff continued winter surveillance for adult Ixodes pacificus (Western black-legged ticks). Ticks are collected by dragging a 1 meter square piece of white flannel over the vegetation alongside trails. Laboratory staff have begun testing collected Ixodes pacificus ticks for the presence of bacteria Borrelia burgdorferi, Borrelia miyamotoi and Anaplasma phagocytophilum. Parks that were surveyed in March were Año Nuevo and Memorial Park near Pescadero, and Big Canyon Park and Eaton Park in San Carlos.
West Nile virus season begins in California in mid-April. The District protects residents from this mosquito-borne disease with control that targets mosquitoes in the larval stage, mosquito population monitoring, disease surveillance and public education. The laboratory staff is prepared to conduct disease surveillance in three main ways:
District Laboratory Director Angie Nakano and vector ecologist Tara Roth attended an educational seminar on bed bugs presented by Clark Pest Control on Feb 6. Information was provided on proactive approaches to preventing the spread of bed bugs, prevailing trends in treatment options, and legal issues relating to bed bug infestations, especially in regards to landlord/tenant issues.
During February, laboratory staff continued winter surveillance for adult Ixodes pacificus (Western black-legged ticks). Ticks are collected by dragging a 1 meter square piece of white flannel over the vegetation alongside trails. Ixodes pacificus ticks will be tested for the presence of bacteria Borrelia burgdorferi, Borrelia miyamotoi and Anaplasma phagocytophilum.
The biannual Vertebrate Pest Control Conference was held February 26 – March 1 in Rohnert Park. This conference, hosted by the University of California Division of Agriculture and Natural Resources, covers a variety of topics in pest control, such as commensal and field rodents, vertebrate control materials, bird management and wildlife disease. The first day of the conference was a field trip focusing on human-wildlife conflicts in Sonoma County. Most of the District staff had the opportunity to attend at least part of the conference.
On January 29, Vector Ecologist Dr. Tara Roth gave a presentation at the annual conference of the Mosquito and Vector Control Association of California in Monterey, CA. Tara received her PhD in August of 2016 from University of California, Davis, where she researched the vector-borne disease tularemia. Surveillance for tularemia in San Mateo County will be beginning soon through cooperation with the California Department of Public Health.
During January, laboratory staff continued winter surveillance for adult Ixodes pacificus (Western black-legged ticks). Ticks are collected by dragging a 1 meter square piece of white flannel over the vegetation alongside trails. Ixodes pacificus ticks will be tested for the presence of bacteria Borrelia burgdorferi, Borrelia miyamotoi and Anaplasma phagocytophilum. Parks that were surveyed in January were Thornewood Open Space Preserve near Portola Valley and Memorial County Park near Pescadero.
Winter is adult Ixodes pacificus (western black-legged tick) season in California. Laboratory staff have begun surveillance of this tick and the disease-causing bacteria they carry in parks and open space throughout San Mateo County. Ticks are collected by dragging a 1 meter square white flannel flag over the vegetation alongside trails.
During the cooler months, when there are fewer mosquitoes flying around and not as many service requests, District staff take the opportunity to plan and prepare for the upcoming West Nile virus season. One change this year will be a discontinuation of the sentinel chicken coop at the Jasper Ridge Biological Preserve in Woodside. After looking at West Nile activity throughout San Mateo over the last decade, District staff decided that the Jasper Ridge coop location was not the best use of surveillance resources.
On December 2, San Mateo Mosquito and Vector Control District laboratory staff helped lead a field trip at Wunderlich County Park for Stanford students learning about tick borne diseases. The class was entitled Parasites and Pestilence and was led by professor and District Trustee Dr. Scott Smith. Students were given tick flags and instructed on basic tick biology as well as how to collect ticks and sort by sex and species.
The West Nile Virus season has wrapped up for the year, with the final chicken bleeding on October 30. Although one bird tested positive in January, the District did not detect any evidence of West Nile Virus (WNV), Saint Louis encephalitis, or Western Equine encephalitis in San Mateo County during the active summer season. The surveillance efforts are summarized below:
This summer the laboratory has been assisted by Enger German, who conducted most of the surveillance for invasive Aedes mosquitoes this season. Enger has a master’s degree in Entomology, and experience in insect monitoring, especially in Florida. The District hired Enger for the season using grant funding from Public Health Foundations Enterprises, Inc. on behalf of the California Department of Public Health.
In 2011/2012, lab staff conducted a study in Fair Oaks, an unincorporated area of San Mateo County adjacent to Redwood City, Atherton and Menlo Park, to assess the level of rat activity in the sewer system lines. The County of San Mateo had ended a program to routinely install rodenticide in the sewers. At the time, rat activity was negligible.
As of September 28, 2017, there have been 320 dead birds reported in San Mateo County. Of those, 56 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). Nine dead squirrels and four mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year, and none of them have tested positive.
To some people ticks may all look the same, but for Vector Ecologists at the San Mateo County Mosquito and Vector Control District, knowing the small differences among species can help us learn things such as the potential for disease transmission and distribution. San Mateo County is home to a variety of tick species, many of which residents are unlikely to encounter because of their highly specific habitats. Lab employees however, have the opportunity to collect ticks directly off wild animals when they are captured for disease surveys, in addition to routine tick flagging.
The laboratory was fortunate this summer to have the assistance of recent South San Francisco High graduate Nancy Yip. Nancy was one of two high school interns who did a two month internship at the District the previous summer in 2016. She was willing to return this summer to help the laboratory staff with a variety of monitoring and surveillance programs. In particular, Nancy was especially helpful taking care of the District mosquito colony, recording and entering data, and doing DNA extraction for tick testing. She also participated in field activities.
From January to April of 2017, laboratory staff from the San Mateo County Mosquito and Vector Control District collected ticks from 15 different parks and open spaces around the county. Ticks were tested for three different disease-causing bacteria using the districts quantitative PCR machine. Results displayed on the graph are Minimum Infection Rates (MIR). MIR is an estimated percentage of infected ticks that used when ticks are pooled together before testing to save time and cost. The following pathogens were tested for in the 2017 tick-born disease surveill