San Francisco Chronicle - (Sunday)
Invasive mosquitoes are found in Bay Area
Bay Area authorities are racing to eliminate an invasive mosquito species known to transmit potentially deadly diseases including dengue, Zika and yellow fever.
This week, officials in Santa Clara County announced they had detected six female Aedes aegypti mosquitoes in a residential area of East San Jose. The discovery marked the second appearance of this nonnative species in the South Bay since they attempted to eradicate them in 2022.
“If Aedes aegypti gains a foothold in Santa Clara County, it will not only threaten public health but also affect our quality of life,” the County of Santa Clara Vector Control District said in a statement.
So far, none of the mosquitoes were found to carry any of the aforementioned viruses.
Santa Clara County is home to about 20 native mosquito species, including the common house mosquito, the cool weather mosquito and the Western encephalitis mosquito. These mosquitoes, known to bite during dusk and dawn, transmit diseases like West Nile virus, Western equine encephalitis and St. Louis encephalitis.
The aggressive Aedes aegypti mosquito, originating from tropical and subtropical regions, bites during the day. Because they are not indigenous to California, they adapt to urban environments and residential areas close to human populations. Over the past decade they have been detected in 19 counties across California.
Identifiable by their small size (about a quarter-inch) and black and white stripes on their back and legs, their eggs resemble tiny black seeds and are typically found inside containers such as plant pots, saucers, barrels, bins, buckets and old tires.
In response to the latest infestation, authorities have increased surveillance on Machado Lane near Story Road, where the mosquitoes were detected. They placed a series of traps for adult mosquitoes and their eggs and are conducting door-todoor inspections, instructing property owners to remove standing water sources where Aedes aegypti can lay eggs.
“It’s important for residents in the area to allow district staff to access their properties to check for mosquitoes and treat them as needed,” a county spokesperson said. “East San José residents should inspect their properties for sources of standing water that serve as breeding habitat for mosquitoes and remove them.”
California state officials separately warned of “another long and intense mosquito season,” following unusually high West Nile virus activity in 2023. They attributed climate change, recent heavy rain and flooding as factors creating additional stagnant water habitats for disease-spreading mosquitoes to thrive.
Last year California reported 428 cases of West Nile virus across 34 counties, resulting in 19 deaths. This was more than double the number of cases compared to 2022.
“Last year was a particularly challenging year for mosquito control and 2024 is looking to be equally intense,” Conlin Reis, president of the Mosquito and Vector Control Association of California, said in a statement. “In many parts of the state, mosquito monitoring and treatment efforts are starting earlier in the year and extending late into fall, creating longer mosquito seasons.”
To protect against mosquitoes and the diseases they carry, experts recommend taking the following steps:
• Use insect repellent with EPA-registered active ingredients like
DEET, picaridin, oil of lemon eucalyptus or IR3535, following label instructions.
• Wear long sleeves and pants, especially during dawn and dusk when mosquitoes are most active.
• Install and maintain screens on windows and doors to keep mosquitoes out.
• Remove standing water sources on your property such as flowerpots, tires and buckets, as mosquitoes breed in standing water.
• Fix leaks or broken sprinklers contributing to standing water.
• Clean clogged rain gutters.
• Report neglected swimming pools and daybiting mosquitoes to local mosquito control.