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
Laboratory staff conducted three surveys of wild rodents in the months of July and August. The surveys took place in Montara on July 17th and 18th, at Water Dog Lake park in Belmont on August 15th and 16th and Eaton and Big Canyon parks in San Carlos on August 29th and 30th. Blood samples were taken from captured rodents by a subocular bleed with a microcapillary tube and ear punches were also taken from the rodents at Water Dog Lake, Eaton and Big Canyon parks.
As of August 25, 2017, there have been 286 dead birds reported in San Mateo County. Of those, 52 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
Laboratory staff conducted two surveys of wild rodents in the month of June. The surveys took place in Water Dog Lake park in Belmont on June 14th and 15th and Eaton and Big Canyon parks in San Carlos on June 20th and 21st. Blood samples were taken from captured rodents by a subocular bleed with a microcapillary tube and ear punches were also taken from the rodents. The blood and ear tissue will be tested in our District laboratory for Borrelia bacteria that cause Lyme disease and other infection.
As of June 630, 2017, there have been 215 dead birds reported in San Mateo County. Of those, 45 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
Did you know that there are more stinging insects than just wasps and honey bees? Stinging insects are grouped into the family Hymenoptera and are distinguished by having 2 sets of wings, a cinched “wasp waist,” and an ovipositor that has been modified into a stinger. That is about where the comparisons end however. The following article covers the incredible diversity of stinging insects and even points out a couple of the “wanna-bees” that have evolved to mimic their much more aggressive cousins.
Snipe flies, from the Family: Rhagionidae, are 4.5 to 15 mm long stout bodied flies that can range in color from black to brown and yellow. Though most snipe flies are predators of other insects, one genus (Symphoromyia) has adapted to feeding on mammal blood.
As of June 6, 2017, there have been 134 dead birds reported in San Mateo County. Of those, 21 have been suitable for testing and 1 has tested positive (5%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
Laboratory staff conducted one survey of wild rodents in the month of May. The surveys took place in Montara. Blood samples were taken from captured rodents by a subocular bleed with a microcapillary tube and on nobuto paper strips. This blood was sent to the California Department of Public Health for testing of plague and hantavirus. All rodents tested negative for plague. Results of hantavirus testing are pending.
Starting this year our laboratory will simultaneously test for three encephalitis diseases carried by Culex mosquitoes: West Nile Virus (WNV), Saint Louis Encephalitis (SLEV) and Western Equine Encephalitis (WEEV).
On March 21, the laboratory staff did an annual rodent survey for hantavirus at San Bruno Mountain County Open Space Preserve and State Park. Out of the 43 rodents collected, 5 were positive for hantavirus for an infection prevalence of 11.6%. Results for plague are still pending. The laboratory will schedule a follow-up survey for hantavirus at San Bruno Mountain in the summer and are on-schedule to complete our annual survey for rodent-borne diseases at Montara Mountain in May.
Dr. Nayer Zahiri, laboratory director at the District since November 2012, will be returning to Santa Clara Vector Control as their new District Manager. Nayer’s final day at San Mateo County MVCD will be April 7. During her time with us, Nayer brought her expertise in resistance and molecular biology to develop new laboratory programs for our District, including Q-PCR testing of birds and mosquitoes for West Nile Virus, Q-PCR tick testing for tick-borne bacteria, a robust larval bioassay method for pesticide resistance, and invasive Aedes mosquito monitoring.