Officials: O.C. could see its worst West Nile virus season in county history

Orange County mosquito control officials are urging residents to use mosquito repellent as the county appears on track for, what could be, its worst West Nile virus season on record.

The Orange County Mosquito and Vector Control District said it is seeing unprecedented levels of West Nile virus activity in mosquitoes across the county. West Nile virus is spread when mosquitoes bite infected birds and then transmit the virus.

"We are seeing way more mosquitoes with West Nile than we have ever seen," vector control spokesperson Brian Brannon said.

So far, mosquito traps in 16 Orange County cities have tested positive for West Nile virus. Officials said the highest levels of activity are being detected in the northwestern part of the county, including Fullerton, Anaheim and Buena Park.

"When we see this data coming in, we will expand our traps -- we will look at treating," Brannon said.

District officials said Orange County recorded 186 West Nile-positive samples in 2025. Last week, officials identified 101 positive samples, bringing this year's total to 206.

"Last year was actually a pretty eventful year, where a lot of the activity was happening centralized in Anaheim," vector control ecologist Kiet Nguyen said. "But, if you look at this year exactly at the same time, we have a lot more West Nile virus."

Despite the increase in mosquito activity, there have been no confirmed human cases of West Nile virus in Orange County so far, according to district officials.

According to the Centers for Disease Control and Prevention, most people who contract West Nile virus do not develop symptoms, though some can develop severe illness.

Officials said residents should continue eliminating standing water around their homes, but emphasized that mosquito prevention measures remain important because mosquitoes are expected to persist throughout the season.

"Dusk and dawn are the danger times when you want to make sure to be either wearing repellent or long pants like jeans and long sleeves," Brannon said. "But in this weather, you want to be wearing something with repellent."

Residents experiencing significant mosquito problems in their neighborhoods can submit a service request to the Orange County Mosquito and Vector Control District. The district will respond free of charge on a first-come, first-served basis.