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West Nile Virus resurfaces in Stanislaus County
Statewide, there have been 19 birds and 52 mosquito samples testing positive for West Nile Virus (Photo contributed).

For those looking to escape outside for relaxation, recreation or just to do some needed yard work, Stanislaus County health officials have some advice they hope the public will follow: use mosquito repellant.

The Turlock Mosquito and Eastside Mosquito Abatement districts confirmed the detection of West Nile Virus in two mosquito samples from Stanislaus County. This is the first detection of WNV for both districts in 2020. 

As of Monday, WNV has been detected in six California counties with the WNV activity confirmed in six dead birds, four mosquito samples and no human cases. There have been no WNV human cases or dead birds from Stanislaus County.

This is the earliest detection of WNV the county has recorded since the virus first arrived in 2006.

“The late rains and increased temperatures will hasten the development of West Nile virus in the Central Valley," said Turlock MAD General Manager David Heft. "We urge residents to dump and drain any items around their home that may hold standing water and to use repellent when outside in the dawn and dusk hours."

Mosquitoes become infected with West Nile Virus when they feed on infected birds. Infected mosquitoes can then spread West Nile Virus to humans and other animals when they bite, according to the Centers for Disease Control.

Approximately 1 in 5 people who are infected with West Nile virus will develop symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Less than 1 percent will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). About 10 percent of people who develop neurologic infection due to West Nile virus will die, according to the CDC. People over 50 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and organ transplants, are at greater risk for serious illness.

There are no medications to treat or vaccines to prevent West Nile Virus infection. People with milder illnesses typically recover on their own, although symptoms may last for several weeks or months. In the neuroinvasive forms, patients can suffer severe and sometimes long-term symptoms.

It’s not just the transmission of West Nile Virus that has the area’s mosquito districts concerned. The mosquito breed responsible for transmitting the Zika virus has been detected in Stanislaus County. Aedes aegypti mosquitoes, which are invasive for the region, are capable of transmitting viruses such as chikungunya, dengue, yellow fever, and Zika. 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.

"In 2019, the yellow fever mosquito (Aedes aegypti) expanded their range significantly, expanding northward from Merced county into Stanislaus, San Joaquin, Sacramento, and Placer counties," Heft said. "If residents are experiencing mosquitoes in their backyard during the middle of the day, we definitely want to know about it and residents should call us."

There is no evidence that mosquitos could transmit coronavirus, but contracting WNV could make an exposure to COVID-19 even worse.

"The real concern is coronavirus tends to become more deadly when folks have pre-existing conditions which may weaken their immune system or their ability to fight off the virus," Heft said. "You would not want to be fighting West Nile Virus and coronavirus at the same time, so we're going to do everything we can to keep the mosquito population reduced and minimize the West Nile Virus exposure to people."

The Districts will continue with their surveillance programs identifying mosquito breeding sources and mosquito borne disease activity. They will treat according to their surveillance results. The Districts anticipate more WNV and mosquitoes in the coming months and would like to remind residents they can help by taking the following precautions:

• Dump or drain standing water. These are places mosquitoes like to lay their eggs.

• Defend yourself against mosquitoes by using repellants containing DEET, Picaridin or Oil of Lemon Eucalyptus.

• Avoid being outdoors at dusk and dawn. These are the times when WNV carrying mosquitoes are generally most active.

 •Report neglected swimming pools to your local mosquito abatement district.

• Use tight fitting door and window screens to keep mosquitoes from entering your home.

• Contact your veterinarian for information on vaccinating equine against WNV.

For additional information or to request service, residents should contact their local District Stanislaus County MADs:

• North of the Tuolumne River contact: Eastside Mosquito Abatement District at (209) 522-4098 (

• South of the Tuolumne River contact: Turlock Mosquito Abatement District at (209) 634-1234 (

Reporting and testing of dead birds are important steps in preventing West Nile Virus. A confirmed case of the virus in dead birds or mosquito samples helps to identify areas that need treatment to reduce mosquito activity. To report a dead bird, call the California State hotline at 1-877-WNV-BIRD or report it online at Birds of particular interest are crows, ravens, magpies, jays and raptors (hawk or eagle).