West Nile virus found in mosquito samples in California’s Orange County

Public health officials on July 22 said mosquito samples collected in Anaheim and Garden Grove have tested positive for West Nile virus, the first confirmed virus activity this year.

There have been four positive mosquito samples collected in those cities, according to the Orange County Mosquito and Vector Control District. So far though, no human cases of the West Nile virus have been reported.

A dead bird recovered in Garden Grove also tested positive for the virus, according to a news release.

“Multiple mosquito samples and a dead bird testing positive for West Nile virus indicate that the virus is circulating in the community,” said OC Vector Director of Scientific and Technical Services Amber Semrow in a statement.

“Anaheim and Garden Grove are historically high-risk areas for West Nile virus activity. Conditions across the region are favorable for sustained virus activity during the warm summer months.”

West Nile virus is the leading cause of mosquito-borne disease in the continental U.S., according to the U.S. Centers for Disease Control and Prevention, and is most commonly spread to people through the bite of an infected mosquito.

Mosquito season begins in the summer and continues through fall. In California, there have been three human cases reported this year, one of which was fatal.

In 2024, there was one reported infection of a person with West Nile virus in Orange County and 53 mosquito samples that tested positive.

Residents are asked to drain any standing water on their property to help prevent mosquitoes from breeding.

Other prevention tactics include keeping windows closed that don’t have a screen door, wearing long-sleeved shirts and pants and using insect repellent. Avoiding outdoor activities when mosquitoes are most active during dawn and dusk is also recommended.

Most people infected with West Nile virus won’t develop any symptoms, according to the CDC. About one in five people develop a fever with other symptoms like body aches or vomiting. About one in 150 people develop a severe illness from the virus.

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