West Nile virus is the mosquito illness found in San Diego's mosquitoes.[4]
Keep mosquito illness out of your home with mosquito screens installed by Total Screen.
In this guide we explain: what West Nile virus does to people, who is at higher risk from West Nile virus, & what San Diego County's West Nile records indicate.
The Centers for Disease Control and Prevention tells homeowners to install window screens and door screens to keep mosquitoes out, so get mosquito screens installed today.[7]
Mosquito Illness In San Diego
San Diego County traps and tests its mosquitoes for West Nile virus, through its Vector Control Program, which tracks local mosquitoes.[3]
California recorded 147 human West Nile virus cases and 10 deaths in 2026, as of September 18.[5]
Every number in the County's West Nile reports starts with a trap like this one, set in somebody's yard.
Most people infected with West Nile virus never find out; the CDC puts the share with no symptoms at 80%.[1]
West Nile virus usually produces nothing, but West Nile virus still sends a small number of people to the hospital.[1]
West Nile Virus Symptoms
About 20% of infected people develop flu-like symptoms, the CDC reports.[1]
The CDC lists West Nile virus symptoms as a fever with:
- headache
- body aches
- joint pains
- vomiting
- diarrhea
- rash
Most people who feel anything from West Nile virus feel only those “flu-like” symptoms.[1]
Out of a hundred people infected with West Nile virus, eighty never know it happened.
Less than 1% of infected people develop severe illness affecting the central nervous system, the CDC reports.[1]
Severe West Nile virus illness is rare, and severe West Nile virus illness is serious.[1]
Anyone worried about symptoms after a mosquito bite should speak to a healthcare provider; Total Screen collects public health information and is not a medical authority.
Who Is At Higher Risk From Mosquito Illness
The CDC singles out adults over 65 as most vulnerable to mosquito illness, at three times the likelihood of neurologic illness.[1]
The CDC also warns that people are at higher risk if they have cancer, diabetes, high blood pressure, kidney disease, or a weakened immune system.[1]
The higher-risk hours are the sleeping hours, and an intact window screen covers them without anybody having to think about it.
The Centers for Disease Control and Prevention states that no vaccine and no medicine exist to prevent or treat West Nile virus in people.[2]
Avoiding mosquito bites is the only protection available against West Nile virus.[2]
West Nile Virus Transmission In Neighborhoods
West Nile virus lives in birds first, before West Nile virus reaches any person.[3]
Mosquitoes pick up West Nile virus by feeding on infected birds.[3]
An infected mosquito can then bite more birds, or bite what San Diego County Vector Control calls “accidental hosts,” like horses and people.[3]
West Nile virus circulates between birds and mosquitoes, and when those mosquitoes reach a home, West Nile virus can reach people.
The mosquito that carries West Nile virus is a Culex, and a Culex flies from dusk until dawn.[3]
A Culex that gets indoors will bite through the night, and how to get rid of mosquitoes in your house explains how to clear one out.
A Culex is the plain brown mosquito behind West Nile virus in San Diego, with no back stripe and no banded legs.
A neighborhood with West Nile virus in its birds is a neighborhood where local Culex mosquitoes can pick up West Nile virus.[3]
A dead bird is often the first sign, which is why San Diego County asks residents to report dead bird sightings, such as crows, jays, hawks, and owls.[3]
San Diego County West Nile Mosquitoes
San Diego County traps, batches, and tests mosquitoes all season, alongside the dead birds residents report.[3]
A “batch” is a group of mosquitoes tested together, and San Diego County combines up to 1,000 mosquitoes into one batch.[3]
A “positive batch” means West Nile virus was present in the location where that trap was set.[3]
As of September 17, 2026, San Diego County had found West Nile virus in 45 birds and 87 positive traps.[4]
Trapped mosquitoes are sorted, grouped into batches, and tested together, which is how a positive trap gets counted.
If you have ever wondered “when do mosquitoes come out in San Diego,” click here to find out.
Preventing West Nile Infection
The Centers for Disease Control and Prevention's advice on West Nile virus is simple: avoid getting mosquito bites.[2]
The CDC says preventing mosquito bites is the best way to protect yourself and your loved ones from West Nile virus.[2]
Effective outdoor protection is mosquito repellent and long sleeves, both of which San Diego County officials also recommend.[3][6]
A screen with a hole, a rip, or a gap at the frame is the opening a Culex needs, and an intact screen is not.
For your time spent indoors, the CDC says to “install or repair and use window and door screens”.[7]
Total Screen builds and installs mosquito screens for San Diego homes.
Reduce Your West Nile Risk Today
Homeowners can meaningfully reduce their risk of letting mosquitoes into the house by checking window screens and doors for holes, rips, tears, or bent frames.
If you see that kind of window screen damage, contact Total Screen today.
Total Screen specializes in mosquito screens and bug screens across San Diego, often with a same day or next day appointment.
An intact window screen is the quietest form of West Nile virus prevention there is.
Call Total Screen at (619) 871-7610 for a free on-site estimate.
Or click here to fill out our 2-question contact-form, and we will get back to you right away.
Total Screen repairs, rescreens, and replaces window and door screens throughout San Diego County.
Disclaimer: Total Screen is not a mosquito-control or public-health authority. Nothing here is medical advice, and anyone with questions about symptoms or their own health should speak to a healthcare provider. This article is provided for informational purposes only, and is based on our online research of publicly available documents from the Centers for Disease Control and Prevention, the California Department of Public Health, the County of San Diego and the other sources listed below. To report a mosquito problem, or to ask about treatment on your property, or to report a dead bird, contact the County of San Diego's Vector Control Program.
Sources
- Centers for Disease Control and Prevention — Symptoms of West Nile (“Most people (80%) infected with West Nile virus do not develop symptoms”; “About 20% of people who are infected develop flu-like symptoms, such as a fever with headache, body aches, joint pains, vomiting, diarrhea, or rash”; “Less than 1% of people infected develop severe illness that affects the central nervous system, requires hospitalization, or results in death”; “About 10% of people who develop severe illness affecting the central nervous system die”; people 65+ three times more likely to develop neurologic illness; cancer, diabetes, hypertension, kidney disease and immunosuppression named as higher risk). cdc.gov
- Centers for Disease Control and Prevention — About West Nile (“West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States”; “West Nile virus most commonly spreads to people through the bite of an infected mosquito”; “No licensed vaccines or medicines are available to prevent or treat West Nile virus disease (West Nile) in people”; “The best way to protect yourself and your loved ones from West Nile virus is to prevent mosquito bites”). cdc.gov
- County of San Diego, DEH Vector Control Program — West Nile Virus (mosquitoes acquire the virus by “feeding on infected birds” and “can then bite and infect more birds or can bite and infect accidental hosts like people and horses”; surveillance by “trapping, batching, and testing mosquitoes and by testing dead birds”; “Mosquitoes are combined into batches of up to 1000 individuals for testing” and “Multiple batches can be collected from one trapping event”; residents asked to report “dead birds such as crows, jays, hawks, and owls”; residents advised to “keep screens over doors and windows closed and free of holes or gaps”, to wear long sleeves and pants outdoors and to use insect repellent). sandiegocounty.gov
- County of San Diego, DEH Vector Control Program — West Nile Virus Activity in San Diego County (45 WNV-positive birds and 87 positive traps recorded in 2026 through September 17, 2026). Figures are year-to-date and updated through the season. sandiegocounty.gov
- California Department of Public Health — California West Nile Virus Website (147 human cases across 21 counties and 10 deaths statewide in 2026, as of September 18, 2026; the State reports “the highest levels of West Nile virus activity in five years”). Figures are year-to-date and updated weekly. westnile.ca.gov
- Centers for Disease Control and Prevention — Preventing Mosquito Bites (“Use screens on windows and doors”; “Repair holes in screens to keep mosquitoes outdoors”; “Use air conditioning, if available”). cdc.gov
- Centers for Disease Control and Prevention — Mosquito Control at Home (“Install or repair and use window and door screens”; “Close doors, including garage doors”; “Use air conditioning when possible”). cdc.gov