Santa Cruz County officials are sounding the alarm after an invasive mosquito species capable of spreading dengue, Zika, and yellow fever was detected near downtown Boulder Creek — the second confirmed finding of its kind in the county.
The Santa Cruz County Mosquito & Vector Control District said Monday that Aedes aegypti, an aggressive, day-biting mosquito about a quarter-inch long with distinctive black-and-white markings, was confirmed in the Boulder Creek area by the California Department of Public Health.
The discovery follows a 2022 detection in the southern part of the county that the Vector Control District contained, county officials said.
“This is not a mosquito that naturally occurs here,” county officials said in a statement. “We’re working aggressively to determine how far it has spread and to prevent it from establishing in the community.”
Health officials said that residents who develop fever, headache, or joint pain after traveling to areas where dengue, Zika, or chikungunya are active should contact their doctor and stay indoors to prevent possible spread.
Vector Control District officials have started door-to-door inspections around downtown Boulder Creek to look for standing water where mosquitoes lay eggs. Teams are also deploying specialized traps and collecting water samples to check for larvae.
Residents are being urged to eliminate even small amounts of standing water — like in plant saucers, bird baths, pet dishes, toys, or discarded containers — and to scrub surfaces where mosquito eggs can stick.
County officials encouraged the public to use EPA-registered repellents such as DEET or oil of lemon eucalyptus, wear long sleeves and pants, and make sure window and door screens are intact.
Anyone who experiences daytime mosquito bites or notices unusual mosquito activity is asked to report it to the Santa Cruz County Mosquito & Vector Control at mvc.santacruzcountyca.gov or by calling (831) 454-2590.
A statewide problem
Although Aedes aegypti is not endemic to California, it has become an increasing concern statewide because it can transmit several serious viruses.
Mosquitoes that tested positive for West Nile virus were recently found on an island in the Sacramento-San Joaquin River Delta in eastern Contra Costa County, according to the Contra Costa Mosquito and Vector Control District. The insects were collected from a trap in Holland Tract.
More invasive mosquitoes have also been detected in Antioch, where residents have been urged to dump out any standing water from recent rains. Aedes aegypti mosquitoes were found between Lone Tree Way and Hillcrest Avenue.
The Contra Costa district has been trapping the mosquitoes since May, and just last week, collected additional samples, said Steve Schutz, scientific programs manager for the district.
In 2024, local dengue cases were confirmed in Los Angeles and San Diego counties.