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Mosquito capable of carrying Zika virus found in Stanislaus County
zika mosquito
Aedes aegypti mosquitoes have been detected in Stanislaus County for the first time. These mosquitos are capable of transmitting viruses such as chikungunya, dengue, yellow fever and Zika (Photo contributed).

The mosquito breed responsible for transmitting the Zika virus has been detected in Stanislaus County, the East Side Mosquito Abatement District and Stanislaus County Public Health Agency reported Thursday.

Aedes aegypti mosquitoes have been detected previously elsewhere in California, but never before in Stanislaus County. The breed, which is invasive for the region, is capable of transmitting viruses such as chikungunya, dengue, yellow fever and Zika that are not transmissible by the native Culex mosquitoes.

Aedes aegypti mosquitoes were recorded by the District, initially in a trap located in Modesto just north of the intersection of Lakewood Avenue and Scenic Drive on July 25, and in another trap nearby on July 31.

“We found two male Aedes aegypti in traps within 100 meters of each other, which is indicative of an established breeding population in the community. It is our responsibility to locate and control them,” said East Side Mosquito Abatement District General Manager J. Wakoli Wekesa.

Aedes aegypti mosquitoes pose a threat in that returning travelers may contract these viruses elsewhere, and Aedes aegypti in infested areas may pick them up and transmit to others. While the Aedes aegypti mosquito has the potential to transmit deadly viruses, none of these viruses are currently known to be transmitted locally in California.

In contrast to the native amber-colored Culex mosquitoes, whose peak biting times are dawn and dusk, Aedes aegypti mosquitoes are black and white, bite aggressively during the day, and feed almost exclusively on humans. Additionally, the larvae of Aedes aegypti mosquitoes require much less water. Females lay their eggs just above the water line in small containers and vessels that hold water, such as dishes, potted plants, bird baths, ornamental fountains, tin cans, or discarded tires. The eggs can survive for up to eight months after the water dries out.

District staff will be conducting enhanced surveillance in the area including more trapping to evaluate the extent of the infestation. Mosquito control technicians will be doing door-to-door inspections searching for standing water sources where mosquitoes lay eggs and breed, which will encompass an area about a quarter mile radius from the index location. The technicians will be carrying out inspections and control activities in residents’ yards as needed and educating residents on how to prevent mosquito breeding.

“This mosquito species breeds in small containers in and around homes,” said Wekesa. “To get rid of it, people need to be aware of it, and then prevent its establishment by eliminating standing water in and around their homes.”

Most people testing positive for Zika will have mild to no symptoms. The most common symptoms include fever, rash, conjunctivitis (red eyes), and joint pain and begin three to seven days after being bitten.

Severe illness requires supportive care at a hospital. There is no vaccine or cure for Zika.
The virus is of most concern to pregnant women or women considering getting pregnant in the near future. Zika virus during pregnancy can cause microcephaly and other severe brain defects in infants.  Additionally, there is an association between Zika and Guillain-Barré Syndrome, a disease affecting the nervous system.  

Zika virus can also be transmitted to sexual partners by both males and females. Both men and women of childbearing age should take precautions if they have recently traveled, or plan to travel, to a location where Zika is spreading. The virus can live in men for up to six months and up to eight weeks in women.

Prevent Aedes aegypti development in your yard:

1. Inspect yards for standing water sources and drain water that may have collected under potted plants,

in bird baths, discarded tires, and any other items that could collect water;

2. Check your rain gutters and lawn drains to make sure they aren’t holding water and debris;

3. Check and clean any new potted plant containers that you may bring home from areas that may have Aedes aegypti. The eggs can remain viable under dry conditions for months.

Prevent mosquito bites:

1. Apply repellents containing EPA registered ingredients such as DEET, picaridin, oil of lemon

eucalyptus, or IR3535 to exposed skin and/or clothing (as directed on the product label). DEET can be used safely on infants and children two months of age and older.

2. Wear long sleeve shirts, long pants, socks and shoes when outside.

3. Be sure window and door screens are in good repair to prevent mosquitoes from entering your home.

Residents experiencing mosquito bites should report them immediately to the Mosquito Abatement Districts in Stanislaus County. If you are sick with fever, headache, and joint or muscle pain after returning from an area where dengue, chikungunya, or Zika occurs, contact your doctor and stay indoors as much as possible to avoid mosquito bites and help prevent possible spread of the virus.

The Turlock Mosquito Abatement District can be reached at (209) 634-1234 or online at