Yellow-fever mosquito lands in Bay Area

Town Crier File Photo
The Santa Clara County Vector Control District uses traps to catch and subsequently monitor mosquitoes for yellow fever and West Nile virus.

Just as the local mosquito season comes to an end, a rare type of the insect has surfaced nearby. A yellow-fever mosquito was found Aug. 23 in Menlo Park, according to local county vector control districts.

With origins in Africa, the Aedes aegypti – or yellow-fever mosquito – is approximately 1/4-inch long with a black and white body. Centers for Disease Control and Prevention officials noted that the species is most active two hours after sunrise and two hours before sunset and can even hide in closets during the day. By transmitting the virus from one human or mammal to the next via bites, the species can spread dengue fever and yellow fever. Fresno and Madera counties also identified yellow-fever mosquitoes this summer, but no symptoms of infection were reported in humans.

“It’s important to note that the current risk of disease transmission from this mosquito is extremely low,” said San Mateo County Health Officer Dr. Scott Morrow in a press release. “But we must make every effort to eradicate this mosquito and not allow it to establish itself here to prevent future disease transmission risk.”

The species quickly adapts to new environments, according to CDC officials. Vector control and area agencies responded quickly to eliminate the yellow-fever mosquito threat. In addition to deploying traps to capture adult mosquitoes and mosquito eggs, local agencies conducted door-to-door canvassing near the source in Menlo Park. Such efforts were successful in eradicating the yellow-fever mosquito at the San Francisco Airport in 1979, the last time officials detected the species in the area.

The San Mateo County Mosquito and Vector Control District encourages residents to protect themselves from bites by wearing long-sleeved clothing and applying insect repellents that contain DEET, picaridin or eucalyptus and lemon oil. Vector control officers also request that homeowners eliminate standing water that could expand the mosquito population and make sure that doors and windows are tightly sealed.

It is much more common for mosquitoes to transmit West Nile virus during the local mosquito season, which typically ends in September. California is experiencing an especially active West Nile virus season, with 87 human cases of the mosquito-transmitted disease reported in 23 counties this year. As of Friday, the Santa Clara County Vector Control District completed eight mosquito foggings in San Jose – a procedure completed when infected mosquitoes are found near dead birds, squirrels or other animals that test positive for West Nile. Although vector control confirmed that no dead birds or mosquitoes from Los Altos tested positive for the disease as of last month, a Santa Clara County woman in July became the first county resident to contract the virus since 2011.

For updates and more information, call the Santa Clara Vector Control District at (408) 918-4770 or visit

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