Most people meet West Nile virus through a headline about somebody else’s bad summer. A county sprays. A case count climbs, the story ends in October, nothing sticks. That framing has aged badly. West Nile has been a permanent resident of the lower 48 for most of two decades, so the useful question is no longer whether it is here.

Here are five things worth your attention.

It is endemic now, everywhere, every year

West Nile is established throughout the contiguous United States (3). Not visiting. Established. In 2024, the most recent year with finalized national numbers, 1,808 cases came from 591 counties across 48 states and the District of Columbia (1). That was a quiet year, below the 10-year median of 2,162 (1).

Which states get hit hardest reshuffles every year. Chasing that reshuffle is mostly wasted worry, since Texas had the largest raw count of neuroinvasive cases in 2024 while the highest per-capita rates were in North Dakota (2.76 per 100,000) and Nebraska (2.49), and none of it tells you anything you can act on where you live (1). Timing does. In 2024, 84% of illness onsets fell between July and September (1).

In-season numbers are wrong, and they are wrong in one direction. Through the week ending August 15, 2026, national provisional surveillance listed 228 West Nile cases (2). At the same week of 2025 the published figure was 321, and that identical 2025 window now reads 1,104 after months of revision, meaning roughly seven in ten of that season’s cases for the period had not reached the national count while anyone was looking (2). So a quiet August tells you very little. It is a receipt that the paperwork has not caught up.

The odds, honestly

Most infections do nothing at all. Nothing. Roughly 25% of infected people develop West Nile fever, and between 1 in 150 and 1 in 250 develop neuroinvasive disease, meaning the virus reaches the brain, meninges, or spinal cord (3). Everyone else clears it and never knows. Incubation runs 2 to 14 days, stretching toward 21 in people who are immunocompromised (3).

Hold those numbers next to the surveillance data. Three quarters of reported 2024 cases were neuroinvasive (1). That sounds terrifying until you realize mild illness almost never gets tested, which means the reported count filters for severity rather than counting infections. My honest read: published case numbers undercount infections by orders of magnitude while overstating the danger of one mosquito bite.

The small slice that goes badly, goes badly for a long time

Among the 1,808 reported 2024 cases, 1,396 patients (77%) were hospitalized and 173 died, with the deaths concentrated almost entirely in the neuroinvasive group, 169 of 173, giving a case-fatality rate of 13% among those patients (1). Median age was 64 (1).

Survival is not the whole story. A CDC and Maricopa County study assessed 159 people hospitalized with West Nile in Arizona, 17 to 24 months later. Eighty-three percent still had symptoms, including fatigue, pain, and trouble with sleep and concentration. Forty percent had gone to long-term care. A third reported disability, and 55% rated their health as worse than before the illness (4). Of the people who develop West Nile paralysis, about two thirds keep significant weakness in the affected limbs (3). That is the part I wish got more airtime.

No treatment, no vaccine, and the reason is money

There is no antiviral for West Nile. Care is supportive, and there is no licensed human vaccine either (3). Follow the chain honestly. A mosquito bites you, most likely nothing happens, sometimes you run a fever that clears on its own, and in the small remainder the virus crosses into the brain or the spinal cord, where there is no drug anyone can hand you and nothing that could have been given in advance (3). The 2026 surveillance report puts it plainly. Roughly 25 years after WNV was first detected here, effective tools for diagnosis, prevention, and treatment are still lacking (1).

CDC convened developers and regulators in April 2024 to work out why. The barriers are structural. Transmission is episodic and scattered, which makes a phase III efficacy trial nearly impossible to power. Most infections are silent, which wrecks the clinical endpoint. No surrogate marker predicts protection, and almost no money supports manufacturing a vaccine for a disease reporting a couple thousand US cases a year (5). Candidates looked fine in early trials. None finished. Call it a market failure rather than a research failure.

What that leaves you, and it is unglamorous

Nothing to take, nothing to be vaccinated against. So prevention comes down to not being bitten. I know how dull that sounds. It is still the only lever you have.

Use a repellent registered by the EPA. Registered skin-applied ingredients include DEET, picaridin, IR3535, oil of lemon eucalyptus, PMD, and 2-undecanone (7). Repellent use is associated with lower West Nile risk, yet few people use it regularly even during publicized outbreaks (3). That gap is the whole problem. Reapply on the label’s schedule, not your memory’s. Empty standing water on your property, because the Culex mosquitoes that carry this virus breed in small stagnant collections (3). Fix the screens. The prevention side gets a fuller treatment in an earlier post, Mosquitoes Are More Than a Nuisance to Your Health, if you want the longer version of what mosquitoes carry and how to keep them off you.

Of that list, DEET is the one I tell patients to buy.

Then know what should prompt urgent evaluation. Fever with a headache in mosquito season is common and usually nothing. Fever with new confusion, a stiff neck, tremor, or weakness in an arm or leg belongs in an emergency department rather than on my schedule. I practice entirely by video. Video is good for many things. It is no good for a lumbar puncture.

For clinicians: a few points that change management

Diagnosis rests on West Nile IgM in serum or CSF. The caveat matters, because the antibody is often absent at presentation, so a convalescent sample may be needed (3), and the CSF gives you little to hang a diagnosis on either: normal glucose, protein under 150 mg/dL, moderate pleocytosis under 500 cells per microliter with lymphocyte predominance, though neutrophils can dominate early (3).

Do not anchor on encephalitis. Of the 1,347 neuroinvasive cases in 2024, 852 were encephalitis and 279 meningitis, but 55 presented as acute flaccid paralysis (1). That last group gets missed. Asymmetric weakness with little sensory involvement in a febrile August patient gets worked up as Guillain-Barré for a day or two before anyone orders arboviral serology.

Transfusion transmission has been nearly eliminated by blood donor nucleic acid screening (3), which leaves organ transplant as the residual route, and in 2024 two recipients of kidneys from a single deceased donor died of neuroinvasive disease (1). Counsel survivors and families early. The Arizona data are clear that recovery is often prolonged and sometimes incomplete, and families do better hearing that at discharge than at month nine (4).

The Bottom Line

West Nile is a low-probability, high-consequence problem, the kind humans handle poorly. Your risk from any single bite is small. Genuinely small. The ceiling on a bad outcome is high, nothing exists to catch you if you fall through, and the people who fall are disproportionately over 60. As of August 28, 2026, California had confirmed 65 human cases and 5 deaths across 16 counties, with 3,001 mosquito samples testing positive in 29 counties (6). That one state has accumulated more than 8,000 human cases and over 400 deaths since 2003 (6).

So buy the repellent. Empty the buckets. Learn the handful of symptoms that mean go now instead of wait and see. That is the entire playbook, and I would rather hand you a boring one that works than an interesting one that does not.

Related Reading

Mosquitoes Are More Than a Nuisance to Your Health What Is Hantavirus? What You Need to Know Right Now Why Won’t Antibiotics Cure a Viral Infection? Doctor Explains

Scott Rennie, D.O.
Board Certified in Obesity Medicine and Family Medicine

This blog is for educational purposes only and does not constitute individual medical advice. Always consult your own physician before making changes to your health, medications, or treatment plan.

Sources

1. Mace KE, et al. West Nile Virus and Other Nationally Notifiable Arboviral Diseases, United States, 2024. MMWR Morb Mortal Wkly Rep. 2026;75(29):369-376. Accessed via PubMed Central (secondary host; cdc.gov was returning 403 at the time of writing). https://pmc.ncbi.nlm.nih.gov/articles/PMC13422701/

2. National Notifiable Diseases Surveillance System (NNDSS) Weekly Data, arboviral diseases, West Nile virus disease, MMWR weeks 33 of 2025 and 2026. CDC open data. https://data.cdc.gov/NNDSS/NNDSS-Weekly-Data/x9gk-5huc

3. Petersen LR, Brault AC, Nasci RS. West Nile Virus: Review of the Literature. JAMA. 2013;310(3):308-315. https://pmc.ncbi.nlm.nih.gov/articles/PMC4563989/

4. Fagre AC, et al. Long-term Sequelae Associated With Severe West Nile Virus Disease in Maricopa County, Arizona, 2021. Open Forum Infect Dis. 2026;13(6):ofag295. https://pmc.ncbi.nlm.nih.gov/articles/PMC13234615/

5. Nett RJ, et al. Summary of human West Nile virus vaccine meeting, 2024: Investigating barriers to development. Vaccine. 2025;68:127938. https://pubmed.ncbi.nlm.nih.gov/41197444/

6. California Department of Public Health, West Nile Virus Activity in California, data as of August 28, 2026. https://westnile.ca.gov/

7. US Environmental Protection Agency. Skin-Applied Repellent Ingredients. https://www.epa.gov/insect-repellents/skin-applied-repellent-ingredients