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Yes. In Los Angeles County, infected Culex mosquitoes can transmit West Nile virus (WNV) when they bite people. The county says this mosquito type is found throughout Los Angeles County, so transmission is locally possible wherever infected mosquitoes are present. That does not mean every mosquito carries WNV or that every bite causes infection.
The most useful protection is a layered routine: apply an EPA-registered repellent outdoors, cover exposed skin, take extra care around dawn and dusk, keep window and door screens intact, and remove standing water at least weekly and after rain. The latest county figure available for 2026 was 100 reported WNV infections by September 21, a provisional, season-to-date count rather than a final annual total.
Is West Nile virus in Los Angeles right now?
Los Angeles County reported 100 WNV infections by September 21, 2026. The county described that total as the highest reached by that point in nearly a decade and compared it with 268 cases recorded during the entire 2017 season. Because the 2026 number is a report-to-date surveillance figure, it can change as additional infections are identified and reported.
The season had already produced serious illness. A July 13, 2026 county release described a resident hospitalized with WNV encephalitis after symptoms began in late June. On August 20, the county reported its first local WNV death of the season, caused by severe neurological illness.
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For a completed-year comparison, Los Angeles County’s final 2025 report recorded 22 human WNV infections and two deaths. That report also listed 113 clinical cases in California and 2,076 in the United States during 2025. Those final 2025 totals should not be combined with the provisional 2026 count.
| Measure | Reported figure | How to interpret it |
|---|---|---|
| Los Angeles County, 2026 | 100 infections by September 21, 2026 | Season-to-date figure; not a final annual total |
| Los Angeles County, 2017 | 268 cases for the full season | Full-season comparison cited by the county in 2026 |
| Los Angeles County, 2025 | 22 human infections and two deaths | Final county report for that year |
| California, 2025 | 113 clinical cases | Final statewide count cited by the county |
| United States, 2025 | 2,076 clinical cases | Final national count cited by the county |
WNV activity is seasonal. California public-health guidance says the virus is encountered most often in summer and early fall, when transmitting mosquitoes are active. A low or high count on one date does not tell you whether an individual mosquito is infected, so use precautions whenever mosquitoes are present.
“The first human cases of West Nile virus are an important reminder that we all need to take steps to prevent mosquito bites and mosquito breeding,” said Muntu Davis, MD, MPH, Los Angeles County Health Officer, in the county’s July 13, 2026 release.
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How mosquitoes spread West Nile virus
The bird–mosquito–human cycle
Culex mosquitoes acquire WNV when they feed on infected birds. After the virus is present in the mosquito, a later bite can transmit it to a person. California identifies Culex mosquitoes as the vectors responsible for WNV transmission in the state.
This cycle explains why the presence of the mosquito matters but does not make every bite dangerous. A mosquito must be a transmitting species and must have acquired the virus; many mosquitoes do not meet both conditions.
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When exposure is most likely
California Department of Public Health guidance identifies dawn and dusk as periods when WNV-spreading mosquitoes are especially active. Outdoor activity during those hours deserves extra attention to clothing and repellent. Mosquitoes can also be encountered at other times, so a dawn-and-dusk focus should not be treated as a guarantee of safety during the rest of the day.
Other documented routes
California notes rare transmission through blood transfusions, organ transplants, and from mother to baby during pregnancy. The department characterizes transfusion risk as very low and says it should not deter an emergency or medically necessary transfusion. For ordinary household prevention, mosquito-bite avoidance remains the central concern.
What symptoms can West Nile virus cause?
Most infections have no symptoms
California estimates that about four out of five infected people have no symptoms. About one in five develops symptoms such as fever, headache, or body aches. A person cannot determine from a mosquito bite alone whether infection occurred.
Severe neurological disease
Some infected people develop illness affecting the brain or nervous system, including encephalitis or meningitis. The Los Angeles County reports of a hospitalized encephalitis patient and a death from severe neurological illness illustrate why unusual or serious symptoms warrant prompt medical attention.
Who has a higher risk of severe illness?
California identifies people aged 55 and older as being at greatest risk of severe symptoms. It also lists people with certain conditions, including cancer, diabetes, hypertension, and kidney disease, as well as organ-transplant recipients. Los Angeles County materials describe older adults, including people over 50, and people with health problems as more vulnerable. The agencies use different age wording; neither statement means that younger, healthy people cannot become seriously ill.
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There is no specific treatment for WNV disease and no vaccine to prevent infection, according to the cited 2026 county releases. If fever, headache, body aches, confusion, weakness, stiff neck, or other concerning symptoms develop after possible mosquito exposure, contact a healthcare provider. Do not use this article to diagnose yourself or another person.
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1. Choose an EPA-registered repellent
Use a repellent registered with the U.S. Environmental Protection Agency and follow its label for where, how much, and how often to apply it. Los Angeles County lists DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD), and 2-undecanone. California’s WNV guidance specifically lists DEET, picaridin, oil of lemon eucalyptus, and IR3535.
The evidence supports comparing products by EPA registration, active ingredient, label directions, stated duration, and suitability for the person using it—not by assuming one brand is universally best. A product label is the controlling instruction for application and reapplication.
2. Do not substitute pure essential oil
Los Angeles County specifically says that “pure” oil of lemon eucalyptus that is not formulated as a repellent is not recommended. It has not undergone the same validated testing and is not registered with the EPA as an insect repellent. A registered OLE or PMD formulation is not the same thing as an undiluted essential oil sold for another purpose.
3. Cover skin, especially at dawn and dusk
When practical, wear long sleeves, long pants, and other clothing that reduces exposed skin. Make this routine a priority during early morning and evening outdoor activities, when CDPH says WNV-spreading mosquitoes are particularly active. Clothing does not replace repellent on uncovered skin.
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4. Keep mosquitoes outside
Maintain tight-fitting screens on doors and windows. Inspect frames and mesh for holes, tears, and loose edges, then repair or replace damaged sections. A screen-repair kit or replacement mesh can be useful when it matches the existing frame, but the public-health objective is simply a sound barrier with no openings.
How to remove mosquito breeding sites around your home
Inspect every week
Los Angeles County Environmental Health advises tipping out or draining standing water at least weekly and again after rain. Walk the property rather than checking only the most obvious container; small amounts of water can remain in ordinary household items.
- Empty buckets, planters, and trash containers that collect water.
- Turn containers upside down or store them under cover so rain cannot refill them.
- Check areas where water remains after irrigation or a storm.
- Repeat the inspection after rain, even if the property was recently cleared.
Deal with neglected pools and larger problems
If a neglected pool or another property condition is producing mosquitoes, contact the appropriate local vector-control district or Los Angeles County Environmental Health channel. The county’s 2026 guidance directs residents to report neglected pools through the county Environmental Health pool channel or the local vector-control district, depending on the location and property type. Environmental Health also lists local vector-control contacts for infestations and questions.
What to do after a mosquito bite
- End the exposure. Move indoors or to a screened area, put on covering clothing, and apply an EPA-registered repellent according to its label before going back outside.
- Check your surroundings. Look for standing water and damaged screens so another bite is less likely.
- Monitor how you feel. Most infections cause no symptoms, but fever, headache, body aches, or neurological symptoms can occur.
- Seek medical advice for concerning illness. Contact a healthcare provider if symptoms develop, especially if you are an older adult, have a listed health condition, or have received an organ transplant. Urgent neurological symptoms require prompt medical attention.
A bite is not proof of WNV infection, and the absence of a noticeable bite does not prove that exposure did not occur. Use symptoms and professional medical advice—not the appearance of the bite—to decide whether evaluation is needed.
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How to plan precautions by season and setting
Summer and early fall
These are the periods California identifies as the usual WNV season. Keep repellent available, check screens before evening activities, and maintain the weekly water inspection instead of waiting for a county alert.
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Backyards, balconies, and shared properties
Containers on balconies, patios, and common areas can hold water just as buckets do. Include planters, discarded items, and trash containers in the inspection. If a source is on neighboring or shared property and cannot be corrected, use the county or local vector-control contact rather than attempting unsafe access.
Outdoor events and commuting
For evening gatherings, arrive with repellent applied as directed and wear clothing that limits exposed skin. For dawn activities, apply the same precautions before leaving home. Screens protect indoor spaces, but they do not protect you once you move outside.
Common mistakes that reduce protection
- Assuming every mosquito is infected: WNV transmission requires a susceptible mosquito to acquire the virus from an infected bird; the presence of mosquitoes alone does not establish infection.
- Using unregistered “natural” oil: Pure oil of lemon eucalyptus is not equivalent to an EPA-registered OLE or PMD repellent.
- Checking water only once: County guidance calls for weekly removal and another check after rain.
- Ignoring small screen damage: A hole or tear defeats the barrier where it occurs; repair or replace it.
- Reading a provisional count as a final total: The 100 Los Angeles County infections reported by September 21, 2026 were season-to-date, while the 22 infections and two deaths from 2025 were final-year figures.
- Waiting for symptoms before preventing bites: Prevention works before exposure; there is no vaccine or specific treatment for WNV disease.
When to contact local officials or a clinician
Contact vector control or Environmental Health when
You see persistent mosquito activity that you cannot resolve, identify a neglected pool, or need help locating a breeding source. Los Angeles County Environmental Health provides local vector-control district contacts and reporting pathways. The correct district or county channel depends on the property’s location and type.
Contact a healthcare provider when
You develop fever, headache, body aches, or any concerning symptom after possible exposure. Seek prompt care for symptoms suggesting neurological involvement, such as confusion, severe weakness, stiff neck, or other changes affecting the brain or nervous system. Tell the clinician about the possible mosquito exposure and any risk factors that apply to you.
Quick Recap
Practical checklist for Los Angeles residents
- Keep an EPA-registered repellent available and check its active ingredient and label directions.
- Apply repellent before outdoor activity, with extra care at dawn and dusk.
- Wear long sleeves and pants when practical.
- Inspect and repair window and door screens.
- Empty or drain standing water every week and after rain.
- Include buckets, planters, trash containers, and less obvious containers in the inspection.
- Report neglected pools or persistent infestations through the appropriate county or local vector-control channel.
- Watch for symptoms and seek medical advice rather than attempting self-diagnosis.
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