County to Hand-Spray Chula Vista Neighborhood in Travel-related Zika Case

County Vector Control crews will hand-spray a Chula Vista neighborhood this week to kill mosquitoes to prevent them from potentially spreading the Zika virus, after mosquitoes were found near a person who contracted Zika while traveling outside the country.

The neighborhood will become the seventh that Vector Control has had to hand-spray to protect the public health this year, but the first in more than three weeks.

Vector Control crews went door-to-door Tuesday to notify residents of the hand-spraying and to tell them how they can keep mosquitoes from breeding in their homes and yards. County crews plan to hand-spray in the neighborhood Thursday, weather permitting.

The area’s borders are D Street to the north, 5th Avenue to the east, Flower Street to the south and midway between 5th Avenue and Broadway to the west.


Two species of invasive Aedes mosquitoes found in San Diego County can transmit Zika virus — and other tropical diseases including dengue and chikungunya — if they first bite an infected person. The hand-spraying will kill adult mosquitoes that could carry and spread the virus. To date, no invasive Aedes mosquitoes in San Diego County have tested positive for carrying any diseases.

The other neighborhoods that have required hand-spraying this year include: South Park on Aug. 19, Mt. Hope on Sept. 6, Adams North on Sept. 9, Grant Hill on Sept. 12, Skyline on Sept. 23 and a neighborhood in Lemon Grove Oct. 3.

County officials continue to urge people to protect themselves from mosquitoes by finding and dumping out all standing water in and around homes so mosquitoes do not have places to breed.

Invasive Aedes mosquitoes are unlike San Diego County’s native culex mosquitoes that can spread West Nile virus in a number of ways. One of the biggest differences is invasive Aedes mosquitoes prefer to bite people during daylight hours, including dusk and dawn. Culex mosquitoes feed at night, including dusk and dawn.

Invasive Aedes species also prefer to live around people — inside and outside homes and in backyards — and can breed in as little as a thimble-full of water. A female mosquito lays 100 to 300 eggs at a time and can potentially lay 1,000 to 3,000 eggs in its lifetime.

To get a better look at the differences between invasive Aedes mosquitoes and our native culex mosquitoes, see the County Fight the Bite’s “Tale of the Tape!”

The Centers for Disease Control and Prevention report that only about 20 percent of people who get infected with the Zika virus ever experience any illness. However, the Zika virus has been linked to a severe birth defect, microcephaly, a condition where babies’ heads and brains are smaller than normal.

Trained County Vector Control technicians will use ultra-low-volume hand-sprayers to apply Pyrenone 25-5, a pesticide approved for use by the Environmental Protection Agency. Pyrenone 25-5 is derived from chrysanthemums, poses low risks to people and pets and dissipates in roughly 20 to 30 minutes. However, the County is instructing residents in the spray areas that they can avoid or minimize their exposure to the pesticide by taking simple steps:

  • Stay inside and bring pets indoors if possible
  • Close doors and windows, and turn off fans that bring outdoor air inside the home
  • Cover ornamental fishponds to avoid direct exposure
  • Rinse fruits and vegetables from your garden with water before cooking or eating
  • Wipe down or cover outdoor items such as toys and cover barbecue grills
  • Beekeepers and those with insects kept outdoors are encouraged to shelter hives and habitats during treatments. Beekeepers are required to register their apiaries with the County’s Department of Agriculture, Weights and Measures to receive advance notice of when a pesticide that may affect bees is applied to blossoming plants in their areas.
  • You may resume normal activities 30 minutes after the treatment

County officials reminded people to follow the County’s “Prevent, Protect, Report” guidelines.

Prevent mosquito breeding

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 unused swimming pools, ponds, fountains and horse troughs.

Protect yourself from mosquito bites

Protect yourself from mosquito-borne illnesses by wearing long sleeves and pants or use 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 possible mosquito activity

Report if you are being bitten by mosquitoes during daylight hours, or if you find mosquitoes that match the description of Aedes mosquitoes by contacting the Vector Control Program at (858) 694-2888.

Information about the Zika virus, chikungunya, and dengue can be found on the Centers for Disease Control and Prevention’s website.

For more information about mosquito-borne illnesses, go to San Diego County’s “Fight the Bite” website. You can also get more information about how the County works to trap and test invasive Aedes mosquitoes, and hear how the public can help prevent mosquitoes from breeding in the following videos.





Gig Conaughton is a communications specialist with the County of San Diego Communications Office. Contact