Mosquitoes in Southern California no longer keep to the warm months, and in 2026 the illness they can carry, West Nile virus, has risen to its highest level in five years. Most children who meet it never feel a thing, while a small minority meet fever, rash, or, rarely, a serious threat to the brain and spinal cord. Public health physicians and hospital epidemiologists are now reminding families that the old seasonal rhythm has loosened, and that a few simple habits, repelling skin, covering limbs, and emptying standing water, remain the most reliable shield between an ordinary itch and a grav
Mosquito Bite Prevention Can Help Protect Children From West Nile Virus as California Cases Hit a Five-Year High
Less than 1% of infected children may develop serious central nervous system illness such as encephalitis, meningitis, or acute flaccid myelitis.
In Southern California, mosquitoes don't wait for summer.
Mosquitoes in Southern California no longer keep to the warm months, and in 2026 the illness they can carry, West Nile virus, has risen to its highest level in five years. Most children who meet it never feel a thing, while a small minority meet fever, rash, or, rarely, a serious threat to the brain and spinal cord. Public health physicians and hospital epidemiologists are now reminding families that the old seasonal rhythm has loosened, and that a few simple habits, repelling skin, covering limbs, and emptying standing water, remain the most reliable shield between an ordinary itch and a grave illness.
In Southern California, mosquitoes no longer wait for summer. Several species bite all year, and usually the bite brings nothing more than a red, itchy bump. But the insects can also carry West Nile virus, and in 2026 infections in California climbed to a five-year high, with the heaviest concentrations in East Los Angeles, the San Fernando Valley, and the South Bay, including Long Beach and Cerritos. Unusually warm, rainy, humid weather, such as El Niño, and milder winters have let mosquitoes thrive for longer stretches of the year.
Michael Smit, MD, MSPH, hospital epidemiologist at Children's Hospital Los Angeles, points families to guidance from county and state public health departments. Most infected children never develop symptoms. About one in five may have a fever, headache, body aches, nausea, or a rash. In fewer than 1% of cases the virus reaches the central nervous system, causing encephalitis, meningitis, or acute flaccid myelitis. Those cases are emergencies, marked by high fever, neck stiffness, confusion, muscle weakness, or tremors. When a parent is unsure, a pediatrician or CHLA's Symptom Checker can help.
Prevention begins with EPA-registered repellent on exposed skin, which is considered safe for children two months and older when used as directed. Physical barriers come next: netting over strollers and car seats, loose long sleeves and pants, screens on open windows, and clothing treated with permethrin. The last step is removing standing water, where mosquitoes breed. With warm conditions lingering, families are being asked to keep all three habits in place.
In Southern California, mosquitoes don't wait for summer. Several species can bite all year, and most of the time the result is nothing worse than a red, itchy bump. But the same insects can carry West Nile virus, and in 2026 infections in California climbed to a five-year high.
The heaviest concentrations of cases have been reported in Southern California: East Los Angeles, the San Fernando Valley, and parts of the South Bay including Long Beach and Cerritos. One reason mosquito activity has been running higher in recent years is weather. Unseasonably warm, rainy and humid patterns such as El Niño help mosquitoes thrive, and milder California winters mean they can stay active at any time of year.
Michael Smit, MD, MSPH, is the hospital epidemiologist and Medical Director of Infection Prevention and Control at Children's Hospital Los Angeles. He points families to guidance from the Los Angeles County Department of Public Health and the California Department of Public Health. That advice includes using EPA-registered insect repellents, wearing long sleeves and pants, and draining standing water around the home.
For most people, West Nile is mild or invisible. Most children who are infected never develop symptoms. About 20% may develop West Nile fever, which can bring fever, headache, body aches and joint pain, nausea or vomiting, and a rash.
In fewer than 1% of infections, the virus reaches the central nervous system and causes West Nile encephalitis, meningitis, or acute flaccid myelitis. That is a medical emergency requiring a trip to the emergency department. Warning signs include high fever, neck stiffness, disorientation, muscle weakness and tremors. For milder symptoms when a parent is unsure whether to seek care, CHLA offers a Symptom Checker, and a pediatrician is another option.
The prevention advice starts with repellent on exposed skin. Products registered with the EPA are confirmed safe and effective, including for pregnant and breastfeeding women. For children 2 months and older, common options contain DEET at 20% to 30%, picaridin at 10% to 20%, or 2-undecanone at 7.5%. Less common options for children 3 and older include oil of lemon eucalyptus (also called PMD) and IR3535. The percentage on the label indicates how long protection lasts. Doctors recommend lower concentrations for children; a 10% DEET product protects for up to two hours. Labels should be read closely and followed.
Physical barriers come next. Insect netting can cover strollers, car seats and playpens outdoors. Babies and children should wear loose, long-sleeved shirts and long pants, layered when possible. Window screens should be installed on open windows and checked for holes. Outer clothing can be treated with a 0.5% permethrin spray according to the directions, and the treatment can last through multiple washes.
The third step is to reduce the places where mosquitoes breed, since they favor moisture and humidity. Clearing standing water protects a household and its neighbors. With warm conditions persisting in Southern California, that combination of repellent, covered skin and dry yards is what families are being asked to maintain.
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Follow the advice on the LA County and California public health websites: use EPA-registered repellents, wear long sleeves and pants, and drain standing water around your home.— Michael Smit, MD, MSPH, Children's Hospital Los Angeles (paraphrased)
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