West Nile Virus SurveillanceThe District’s West Nile virus surveillance program reports several types of positive West Nile virus results, including dead birds, mosquito samples (“pools”), sentinel chickens, and human cases.
Tick-borne disease pathogens in San Mateo CountyOver the past several years, staff have collected more than 30,000 ticks from around the County. Our laboratory staff identify and test these ticks for:
2026 Service RequestsThe total number of service requests in March were well above average (377 compared to a five-year average of 214 in March). Mosquito-related service requests were especially high, with 186 this March compared to a five-year average of 84. Unusually warm weather led to greater insect activity, including mosquitoes and similar flies. Yellowjackets/wasp service requests were also much higher than…
2026 Mosquito SurveillanceIn March, adult mosquito counts of all species remained low, but started to rise as winter transitioned into spring. March was the first detection this year of adult Aedes sierrensis, the Western tree hole mosquito. As the common name suggests, this mosquito usually breeds in water collected in holes in trees. In San Mateo County, the abundance of adult Ae. sierrensis usually peaks in May.
