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County officials to take next steps to eradicate invasive mosquito species

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Santa Clara County officials will spray an East San Jose neighborhood with a bacterial spray next week in their latest attempt to eradicate an invasive species of mosquito found last month.

Since early April, county officials have discovered 12 female Aedes aegypti mosquitoes in a residential area near Machado Lane, off Story Road. These mosquitoes are invasive to the area and can carry several illnesses, like Zika, dengue, yellow fever or chikungunya. Zika can especially be dangerous to pregnant people because it can cause birth defects and problems for the infant.

“It is challenging, but we’re trying our best to make sure this mosquito isn’t going to be established,” Nayer Zahiri, manager of the Santa Clara County Vector Control District, said at a news conference Friday.

On Wednesday morning, authorities said, they will spray the area with a pesticide that targets the mosquitoes’ larvae. The treatment, known as Wide Area Larvicide Spraying, lasts two hours and is derived from a naturally occurring bacteria that is nontoxic to humans, beneficial insects and other forms of wildlife. The county is planning on spraying the area several times over the next few months.

Zahiri said that the threat posed by the mosquitoes remains low, and the rare cases of illnesses associated with Aedes aegypti in the county came from people who traveled to places where the mosquito is endemic or established. Since April, the area of concern expanded to include about 118 acres of the East San Jose neighborhood, encompassing more than 250 properties, said Noor Tietze, scientific-technical services manager at the Santa Clara County vector control district.

Earlier, county officials had responded to the infestation with surveillance, which involved workers setting up traps along Machado Lane, inspecting properties for mosquito larvae and standing water, and eliminating any larvae.

A captured mosquito is shown during Santa Clara County Vector Control District's demonstration on how its staff retrieves mosquitoes out of an invasive mosquito trap on Oct. 25, 2022, in Milpitas, Calif. (Dai Sugano/Bay Area News Group)
A captured mosquito is shown during Santa Clara County Vector Control District’s demonstration on how its staff retrieves mosquitoes out of an invasive mosquito trap on Oct. 25, 2022, in Milpitas, Calif. (Dai Sugano/Bay Area News Group) 

Two of the invasive pests were found in Santa Clara County at Newby Island Landfill in October 2022 and were eradicated quickly.

However, the most recent infestation, in a residential area, is more difficult to stamp out, said Edgar Nolasco, director of the Santa Clara County Consumer and Environmental Protection Agency. According to a county press release, more mosquitoes were found in an area with a lot of people — ahead of the warmest months of the year, when mosquitoes are more active.

“Controlling the population isn’t easy because the Aedes aegypti mosquito is adaptive to any environment and they bite other mosquitoes, making them harder to control,” Zahiri said. “Breeding is another challenge because they prefer to lay eggs in small containers, so it’s hard to find all the sources of breeding.”

Aedes aegypti mosquitoes are about a quarter-inch long and are recognizable by black and white stripes on their bodies and legs. Their eggs are tiny and can look like bits of dirt to the naked eye. These mosquitoes prefer to lay eggs above the water line in small, artificial sources of water, such as buckets, pet dishes, fountains and bid baths, plant pots and saucers, and old tires.

County officials said they don’t know how the mosquitoes arrived in East San Jose. They hypothesized that the insect’s eggs may have been unknowingly transported into the area — which is possible because the eggs can survive without water for at least a year.

Aedes aegypti mosquitoes are dangerously persistent and tend to be active at all times of the day and can bite multiple times, officials said. They only move about a block away from where they hatch, making it imperative for people to get rid of any sources of standing water where the mosquitoes could potentially breed and spread.

County officials recommended cleaning and scrubbing bird baths, pet dishes and other containers to remove any lingering eggs, and asked residents to properly screen rain barrels, cisterns and irrigation drains to prevent mosquito access.

County officials also recommended that people protect themselves from mosquito bites by applying insect repellants with EPA-registered ingredients, like DEET, picaridin, IR3535 or oil of lemon eucalyptus while following label instructions. They also suggested that people wear long-sleeve shirts, pants, socks and shoes when mosquitoes are most active and to make sure window and door screens are in good condition.



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