Orange County’s Mosquito and Vector Control District has confirmed an outbreak of a mosquito-borne illness that can be deadly.
Last week, the district saw over 101 mosquito pools — mosquitoes collected in batches — test positive for West Nile Virus, spreading county-wide. The city at most risk for the virus is Fullerton, with 39 of the 101 samples testing positive within the city.
Buena Park and Anaheim are also confirmed to be at-risk, with Cypress potentially being next in the future.
“We are well on track to have a bad year of West Nile Virus,” said district spokesman Brian Brannon.
The district helps to control vector and mosquito-related problems within the county. One of the ways they do this is by setting up routine traps for these insects and animals to observe weekly.
According to data from the district, the number of West Nile positive mosquito pools at the end of 2025 came out to 186, leading the district to estimate that the county will potentially be dealing with 500 positive samples county-wide by the end of 2026.
West Nile Virus originated in Africa before spreading to the eastern U.S. in 1999. Since then, the virus has spread across the country, with the Center for Disease Control and Prevention stating the illness is the leading cause of mosquito-borne disease in the U.S.
The specific type of mosquito that carries the virus is the Culex mosquito. Infected mosquitoes usually bite birds, easily spreading the virus around different populations of the animals. However, when birds aren’t around, they’ll bite anything, including humans.
According to the CDC, the virus can cause mild symptoms such as a fever, vomiting and body aches. Severe symptoms can affect a person’s central nervous system or illness resulting in hospitalization or death.
Humans are known to be dead-end hosts, meaning that if a person becomes infected with the virus, they will not be able to spread it to others except through organ transplants or blood transfusions.
While most human infections are asymptomatic, the CDC reports that if people do experience symptoms, there are no licensed vaccines or medicines available to prevent or treat the virus.
“For humans, the asymptomatic rate is fairly high by 80%,” Vector Ecologist Kiet Nguyen said. “What we have to worry about is the other 20% that show symptoms, are symptomatic, that can get seriously ill from it via West Nile fever or neuroinvasive disease.”
“The severe case of West Nile Virus is encephalitis, meaning bacterial encephalitis to the spine and the head, and it can actually kill people and paralyze people,” Nguyen continued. “When it does get people sick, it’s pretty heavy, and it’s really targeted towards the elderly and to the youth.”
Nguyen explained that Orange County residents can easily protect themselves from getting bitten during the busy summer season.
“I think repellency is the best way to do it — as long as it’s EPA-approved and FDA-approved. Those are good things. So DEET, Picaridin, I think lemon and eucalyptus is an extract that works very well. I use lemon and eucalyptus,” Nguyen said.
Representatives from the district also recommend wearing long sleeve shirts and pants in order to prevent mosquitoes from biting.
Reducing sources for mosquito larvae to grow in also plays a big part in minimizing bites throughout the year. Standing water should be dumped and drained once a week. By doing so, any bacteria or larvae growing in the water will be killed.
Since ponds or water features outside homes could be a potential breeding ground for the insects, the district gives out free mosquitofish. These fish eat mosquito larvae and pupae to prevent the emergence of adult mosquitoes.
“Any type of repellency is the way to go right now,” Nguyen said.
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