Mosquito illness in San Diego means West Nile virus, and the County traps and tests mosquitoes for it all season.
Mosquito window screens keep biting mosquitoes out of your home, so click here to contact Total Screen, today.
In this guide, we will explain what West Nile virus does to people, who is at higher risk, and what the County actually finds here.
West Nile virus reaches people through mosquito bites, so get mosquito screens installed before the season turns.
What Mosquito Illness Means In San Diego
West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States, which is the CDC's own wording.[2]
West Nile virus is also the mosquito illness San Diego County traps and tests for.[3]
The tropical illnesses people ask about belong to a different insect, the tiger mosquito.
This is the tiger mosquito, not the Culex that carries West Nile virus in San Diego.
Most people infected with West Nile virus never find out, because the CDC puts the share with no symptoms at 80%.[1]
A mosquito illness that usually produces nothing at all still sends a small number of people to hospital.[1]
The honest picture is an infection that is usually invisible and occasionally serious.[1]
What West Nile Virus Does To People
About 20% of infected people develop flu-like symptoms, which the CDC lists as fever with headache, body aches, joint pains, vomiting, diarrhea or rash.[1]
Flu-like is the whole of it for most of the people who feel anything at all.[1]
A summer fever in San Diego is far more likely to be something else.
Out of a hundred people infected, eighty never know it happened.
Less than 1% of infected people develop severe illness, which the CDC describes as affecting the central nervous system, requiring hospitalization, or resulting in death.[1]
Severe West Nile illness is rare and it is serious, and the CDC reports that about 10% of those cases are fatal.[1]
Anyone worried about symptoms after a mosquito bite should speak to a healthcare provider rather than to a screen company.
Who Is At Higher Risk
Adults over 65 are the group the CDC singles out, at three times the likelihood of neurologic illness compared with people under 65.[1]
The CDC also names people with cancer, diabetes, hypertension or kidney disease.[1]
People whose immune systems are suppressed are on the same list.[1]
No vaccine and no medicine exist for West Nile virus, in the CDC's words no licensed vaccines or medicines to prevent or treat it in people.[2]
A disease with no vaccine and no treatment leaves exactly one thing to work with.[2]
Not being bitten is the whole of the defense.[2]
How West Nile Virus Moves Through A Neighborhood
West Nile virus lives in birds before it reaches anyone, and the County describes mosquitoes picking it up by feeding on infected birds.[3]
An infected mosquito can then bite more birds, or bite what the County calls accidental hosts like people and horses.[3]
Accidental is the useful word, because a person is a dead end for the virus rather than a link in the chain.[3]
The virus circulates between birds and mosquitoes, and a person is where it stops.
The mosquito carrying West Nile virus is a Culex, the one that flies from dusk to dawn rather than in daylight.[3]
A neighborhood with infected birds is a neighborhood where the local mosquitoes have something to pick up.[3]
The County asks residents to report dead birds such as crows, jays, hawks and owls, because a dead bird is often the first sign.[3]
What The County Actually Finds Here
San Diego County traps, batches and tests mosquitoes all season, alongside testing the dead birds residents report.[3]
Through September 17, 2026, County testing had found West Nile virus in 45 birds and in 87 positive traps.[4]
Positive traps are not an outbreak, and they are not nothing either.
Every positive batch is a real trap in a real neighborhood, which is what makes the number worth publishing.
California had recorded 147 human West Nile cases across 21 counties as of September 18, 2026, with 10 deaths statewide.[5]
A statewide figure in the low hundreds, in a state of roughly forty million people, is the scale to keep in mind.[5]
Where those cases land is a question of geography, and when do mosquitoes come out in San Diego covers the coastal and inland split.
What Actually Lowers The Risk
The CDC's advice for West Nile virus is to prevent mosquito bites, which the CDC calls the best way to protect yourself and your loved ones.[2]
Repellent and long sleeves work outdoors, and the County recommends both.[3]
Neither one does anything for the hours spent asleep indoors.
Closed and sound is the whole of the advice, and it costs nothing to check.
The County names screens by name, advising residents to keep screens over doors and windows closed and free of holes or gaps.[3]
Free of holes or gaps is the part that decides whether a screen is doing anything, which is what can mosquitoes get through window screens works through.
A screen keeps the next one out and does nothing about the ones already indoors, which is what how to get rid of mosquitoes in your house is for.
Lower The Odds Before The Season Turns
Nothing about West Nile virus is worth panic, and the one control anybody has is not being bitten.
The second-best time to check your screens is today.
Total Screen repairs, rescreens & replaces window and door screens across San Diego, often with a same day or next day appointment.
A sound screen is the quietest form of 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'll get in touch right away.
Let's get every opening in your home closed to the mosquitoes that carry West Nile virus.
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”; 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). Figures are year-to-date and updated weekly. westnile.ca.gov