A woman stands in the center of a research lab
Nayer Zahiri, manager of the County of Santa Clara Vector Control District, speaks about the threat of yellow fever-carrying mosquitoes to public health in Santa Clara County on April 11, 2024. Photo by Brandon Pho.

Santa Clara County officials are prepping to remove a foreign, invasive and aggressive yellow fever mosquito species that’s returned to the region just in time for peak mosquito season.

It was easy to eradicate the species after it first arrived in the county in 2022, when vector officials trapped and removed two mosquitoes in a North San Jose industrial area lacking water. But now six have been found in a residential area along Machado Lane in East San Jose, where there is more water and concern that warmer summer months could lead to a major problem.

“If you eliminate the water, you eliminate the possibility of reproducing and getting established. But if we find more and the community doesn’t do their part to help us, we will then be switching to using pesticides and fogging at people’s residences,” Santa Clara County Consumer and Environmental Protection Agency Director Edgar Nolasco told San José Spotlight.

Nolasco added that vector workers won’t be going into people’s homes, but they will start spraying yards.

The county’s vector control lab studies mosquitoes to monitor their prevalence and threat to public health. Photo by Brandon Pho.

County vector workers say none of the mosquitoes they’ve found were carrying the diseases this species is known to transmit, including yellow fever, dengue, chikungunya and Zika. But that can change if someone returns to the county after traveling from parts of the world where the viruses are prevalent.

Symptoms of yellow fever include a fever with aches and pains to severe liver disease with bleeding and yellowing skin or jaundice, according to the Centers for Disease Control and Prevention.

Officials expect to find more mosquitoes that can carry the disease and are asking residents to remove anything in their yards that might contain even the smallest amounts of standing water — gardening pots, vases, even discarded tires — to prevent the species from reproducing in Silicon Valley. For now, all the mosquitoes they know about were located through carbon dioxide traps they set.

While not native to California, the yellow fever mosquito is present in 19 counties throughout the state, mostly in the Central Valley and Southern California.

If the yellow fever mosquito gains a foothold in Santa Clara County, officials said it will threaten public health and residents’ quality of life, as this species is aggressive and active during the warm parts of the day, unlike native mosquitoes which are most active in the cool mornings and evenings.

The rainy months have helped refill the region’s reservoirs and groundwater — but with that comes a tradeoff of breeding grounds for mosquito larvae, said San Jose Councilmember Peter Ortiz, whose district spans the East San Jose area where the mosquitoes were found.

“I’m confident that our County Vector Control is on the case and working to treat areas where mosquitoes are congregating, as well as educating residents about dumping standing water,” Ortiz told San José Spotlight.

The county already controls the more common West Nile virus-carrying mosquitoes. But the mosquitoes carrying yellow fever will require a different response, county officials said. These mosquitoes travel shorter distances and the effort to stamp them out will be more concentrated.

“We do interview people when we go door-to-door. Questions would be asked if they had any travel from Southern California or brought some plants — those are common sources,” County Vector Control District Manager Nayer Zahiri told San José Spotlight. “But we have not learned as of now the origin of these mosquitoes.”

Contact Brandon Pho at [email protected] or @brandonphooo on X, formerly known as Twitter. 

Comment Policy (updated 5/10/2023): Readers are required to log in through a social media or email platform to confirm authenticity. We reserve the right to delete comments or ban users who engage in personal attacks, hate speech, excess profanity or make verifiably false statements. Comments are moderated and approved by admin.

Leave a Reply