The discovery marks the seasonal return of the virus to the region.
West Nile virus appears annually in the San Gabriel Valley during warmer months.
“West Nile virus is a recurring concern in our region,” said Tristan Hallum, director of scientific programs for the district.
“It’s endemic to the San Gabriel Valley, meaning we expect to detect it every year in mosquitoes, birds, and occasionally humans.”
Higher overnight temperatures during summer accelerate mosquito breeding and viral transmission.
“There is no vaccine or cure for West Nile virus in humans,” Hallum said. “The best method of protection is prevention.”
Most people infected with West Nile virus show no symptoms.
One in five develop fever, headache, body aches, nausea or skin rash that can persist for days or even months.
The statement said severe cases requiring hospitalization affect one in 150 infected people.
These patients may experience high fever, muscle weakness, neck stiffness, coma, paralysis or death.
Adults over 50 and people with compromised immune systems face the highest risk of serious illness, according to the San Gabriel Valley Mosquito & Vector Control District.
Those with chronic health problems also have increased vulnerability.
The Los Angeles County Department of Public Health reports that infected mosquitoes spread the virus through bites.
Not all mosquitoes carry the virus, but the species that transmits it lives throughout Los Angeles County.
The district will continue monitoring disease activity and controlling mosquitoes in public areas through inspections and treatments.
Officials underscore that residents must also take action to reduce mosquito populations.
The district recommends removing stagnant water around homes weekly and discarding unused containers that collect water.
People should protect themselves from bites using insect repellent containing picaridin, DEET, oil of lemon eucalyptus or IR3535, the San Gabriel Valley Mosquito & Vector Control District said.
These ingredients have approval from the Centers for Disease Control and Prevention.
The San Gabriel Valley Mosquito & Vector Control District is one of five vector control agencies in Los Angeles County.
Staff monitor stagnant water sources year-round, including gutters, storm drains and abandoned swimming pools.
The agency uses traps to track adult mosquito populations and tests female mosquitoes for disease.
For more information, call (626) 814-9466 or visit SGVmosquito.org.
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