Health Officials Urge Californians to Remove Standing Water

California Department of Public Health (CDPH) Director and State Public Health Officer Dr. Karen Smith calls on the people of California to help reduce the number of mosquitoes by eliminating standing water, especially in areas that have recently had rain and continue to experience warm temperatures.

"Rainy weather can create new breeding grounds for mosquitoes if water is allowed to pool and remain stagnant," said CDPH Director and State Public Health Officer Dr. Karen Smith. "Aedes mosquito season in California peaks in October, making it critically important that Californians take action to empty even small amounts of water from our gardens and yards."

To help control mosquitoes, check your yard weekly for water-filled containers. Clean and scrub bird baths and pet watering dishes weekly, and dump the water from dishes under potted plants. Contact your local vector control agency if you detect unusual numbers of mosquitoes or you are being bitten during the day.

The Aedes aegypti mosquito, an aggressive mosquito that bites during the day, has been detected in 12 California counties. This black-and-white striped mosquito has the potential to transmit Zika and other diseases, such as dengue fever, chikungunya and yellow fever. While the mosquito is especially active two hours after sunrise and several hours before sunset, it can also bite during the day. These mosquitoes often enter buildings through unscreened windows and doors and bite people indoors.

While there has been no local transmission of Zika in California, as of September 23, 302 travel-associated cases have been reported in the state.

Zika symptoms typically include a fever, rash, joint pain and red eyes. Most people infected with the Zika virus will not have symptoms, but Zika is a major concern in pregnant women because it can cause severe birth defects. In addition to Zika, West Nile virus, another mosquito-borne illness, continues to concern public health officials.

To prevent mosquito bites, apply repellents containing U.S. Environmental Protection Agency-registered ingredients such as DEET, picaridin, oil of lemon eucalyptus, or IR3535 to exposed skin and/or clothing (as directed on the product label). During the times mosquitoes are most active you should wear long- sleeve shirts, long pants, socks and shoes. Be sure window and door screens are in good condition to prevent mosquitoes from entering your home.

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Aedes aegypti and Aedes albopictus Mosquitoes

Two invasive (non-native) mosquito species have recently been found in several California cities (see map below) and there is a potential for them to spread into other areas of California. They are named Aedes aegypti (the yellow fever mosquito) and Aedes albopictus (the Asian tiger mosquito). Unlike most native mosquito species, Aedes aegypti and Aedes albopictus bite during the day. Both species are small black mosquitoes with white stripes on their back and on their legs. They can lay eggs in any small artificial or natural container that holds water.

Aedes aegypti and Aedes albopictus have the potential to transmit several viruses, including dengue, chikungunya, Zika, and yellow fever. None of these viruses are currently known to be transmitted within California, but thousands of people are infected with these viruses in other parts of the world, including in Mexico, Central and South America, the Caribbean, and Asia. The presence of Aedes aegypti and Aedes albopictus mosquitoes in California poses a threat that Zika, dengue, and chikungunya viruses can be transmitted in infested areas from returned infected travelers. Travelers can protect themselves by preventing mosquito bites. When traveling to countries with dengue, chikungunya, or Zika,use insect repellent, wear long sleeves and pants, and stay in places with air conditioning or with window and door screens.