Mosquitoes can carry West Nile virus but San Diego Vector Control is on the case beginning this week with routine aerial larvicide drops. Image via San Diego County Twitter

San Diego County’s Vector Control Program is scheduled to conduct its first routine mosquito-fighting aerial larvicide drop this week on dozens of waterways to help stop mosquitoes from potentially spreading diseases such as West Nile virus, it was announced Tuesday.

Vector control officials are also reminding people to protect themselves from mosquito-borne illnesses by finding and dumping out standing water in and around their homes to keep mosquitoes from breeding.

The county has used helicopters to drop batches of solid, granular larvicide on more than 30 hard-to-reach rivers, streams, ponds and other waterways roughly once a month from April or May through October since West Nile virus arrived here in the early 2000s. The larvicide does not hurt people or pets but kills mosquito larvae before they can grow into biting mosquitoes.

The virus’ effect has been mild in San Diego County in recent years, county officials said, with just one person testing positive for it in 2020, and three in 2019 — all of whom contracted the virus outside the county — with no fatalities.

However, West Nile virus remains a potentially dangerous disease; 22 county residents tested positive for it in 2016 and two people died. Last year across California, 258 people tested positive and 11 people died.

West Nile virus is mainly a bird disease, but it can be transmitted to people and some animals including horses by mosquitoes who first feed on infected birds and then a person or animal.

The larvicide the county uses in its aerial drops kills mosquito larvae who eat it, preventing them from growing into biting adult mosquitoes.

Protecting against mosquitoes has required more help from the public in recent years because of the appearance of a number of types of invasive Aedes mosquitoes who can potentially transmit diseases not naturally found here, including Zika, dengue and chikungunya. While native culex mosquitoes who can transmit West Nile virus breed in larger water bodies reached by the county’s larvicide drops, invasive Aedes mosquitoes prefer to live and breed around people’s homes and yards.

County vector control officials said the best way people can protect themselves is to follow their “Prevent, Protect, Report” guidelines:

— Prevent mosquitoes from breeding by remembering to dump out or remove any item inside or outside of homes that can hold water, such as plant saucers, rain gutters, buckets, garbage cans, toys, old tires and wheelbarrows. Mosquito fish, available for free by contacting the vector control program, may be used to control mosquito breeding in backyard water sources such as stagnant swimming pools, ponds, fountains and horse troughs.

— Protect yourself from mosquito-borne illnesses by wearing long sleeves and pants or use insect repellent when outdoors. Use insect repellent that contains DEET, picaridin, oil of lemon eucalyptus or IR3535. Make sure screens on windows and doors are in good condition and secured to keep insects out.

— Report increased mosquito activity, or stagnant, green swimming pools and other mosquito-breeding sources, as well as dead birds to the County Department of Environmental Health and Quality’s Vector Control Program by calling 858-694-2888 or emailing

–City News Service

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