By Mary O’KEEFE

Earlier this month the first case of West Nile Virus (WNV) infection for the 2026 season was detected in a Los Angeles County resident.

“The person is currently hospitalized after developing WNV encephalitis after symptom onset in late June. The individual lives in the Antelope Valley,” according to the Los Angeles County Dept. of Public Health (DPH). 

“There have been positive mosquito pools as well as dead birds that have tested positive across the County, but this is our first human infection,” said Dr. Aiman Halai, medical epidemiologist, DPH. “But this is our first human infection so this was a person who became symptomatic, was admitted to the hospital and then diagnosed with Neuroinvasive West Nile virus (WNV).”

That is when the virus impacts the central nervous system. Only 1% of people actually are hospitalized with WNV. Many who get the infection are not symptomatic, and some are mildly symptomatic, she added.

“Those people develop a fever, headache, nausea and fatigue. Sometimes a rash but then in its [severest] form … [it] impacts the central nervous system. It can present itself with encephalitis, which is predominantly a lot of confusion and altered mental status; it can also cause meningitis,” Halai said. 

Though most are asymptomatic those with severe symptoms suffer from a variety of symptoms that is common with infections that impact the brain and central nervous system, she added. There is supportive treatment that can manage the infection but for those with most severe symptoms hospitalization is required. 

The absolutely best way to stay safe from WNV is to control the mosquito population and people need to be vigilant. 

“Based on our outreach data, most people understand that mosquitoes grow in stagnant water but are less aware of the types of sources. The district has a robust Vector Control program that helps monitor and control Culex mosquitoes [those that carry WNV] in public spaces, but it’s the private spaces, like backyards and patios, that are the primary breeding spots for Aedes mosquitoes. It’s important people tip, toss and protect. Tip out stagnant water, toss out unused containers and protect themselves from mosquitoes by wearing an EPA-registered repellent that contains one of the following ingredients: oil of lemon eucalyptus, DEET, picaridin or IR3535 when outdoors,” said Anais Medina Diaz, Mosquito Surveillance and Response Plan spokesperson. 

“Other things you can do is wear long-sleeved shirts and pants to provide skin coverage. Mosquitos won’t be able get to the skin to bite. And the third thing would be to prevent mosquitoes to keep from getting inside our homes. We can do that by making sure our windows and doors have screens and that the screens do not have any gaps or holes in them,” Halai said. 

There are some items in backyards, like rain barrels, that collect water. 

“While we should all do our part to conserve and reuse water, we must do it safely so rain barrels don’t breed mosquitoes. We recommend adding mesh to any opening on rain barrel containers to prevent egg laying since the water is likely to be stagnant for some time. Our Vector Control specialists have found rain barrel breeding in neighborhoods with a high mosquito presence, so the threat is real. Residents with rain barrels should also use the collected water within the week to disrupt any potential mosquito larvae and pupae presence. If the water needs to remain for more than a week, residents can purchase an over-the-counter larvicide product that contains Bacillus thuringiensis israelensis at their local home and garden store,” Median Diaz said. 

The San Gabriel Valley Mosquito and Vector Control District monitors the area for elevated presence of mosquitoes and disease presence and that data collected guides their mosquito control response efforts. They have been monitoring WNV in mosquitoes since 2003. They also collect and swab dead birds since WNV is primarily a bird disease and can indicate whether the virus is present in SGV, and reported by the Pasadena Health Dept. and the LA County Dept. of Public Health, according to Median Diaz. 

“In our native Culex species, we routinely test for culex-vectored diseases like West Nile Virus, St. Louis encephalitis, and Western Equine encephalitis. In the past couple of years, we have also tested for Aedes-vectored diseases [Zika, Dengue, Chikungunya] since it appeared for the first time in California in 2023. Testing for these diseases is selective and usually triggered when we’re aware of nearby travel-related cases,” Median Diaz added.