Mosquito-Borne Diseases in the US: West Nile, EEE and Local Dengue
West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States, according to CDC, and caused 1,808 reported cases in 2024. Eastern equine encephalitis is rare but serious, with 19 cases that year. Locally acquired dengue has occurred in Florida, Texas, Hawaii, Arizona and California. Avoiding mosquito bites is CDC's main advice for all three.
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Shop Now →This is a data page. We sell lemon eucalyptus essential oil, which is not an EPA-registered repellent, and nothing here links our oil to any of these diseases or to protection from them. The numbers below come from CDC, with the year attached to each, so you can judge how current they are. For repellents, our overview of whether lemon eucalyptus repels mosquitoes explains the line between registered products and essential oil.
Last reviewed: October 2026. This is a summary of public health reports and not medical advice. If you have a high fever, stiff neck, confusion or weakness, seek medical care right away.
The short version, in one table
| Disease | Latest full-year U.S. count (CDC) | Who is at risk | Key fact |
|---|---|---|---|
| West Nile virus | 1,808 cases in 2024 (10-year median 2,162) | Adults 60 and older and people with certain conditions face higher risk of severe disease | Most infected people have no symptoms; no licensed vaccine |
| Eastern equine encephalitis (EEE) | 19 cases in 2024 | Mostly eastern and Gulf Coast states | About 30% of people with severe illness die, per CDC |
| Locally acquired dengue | 2024: Florida 91, California 18, Texas 1 (CDC advisory, March 2025) | Residents of areas where Aedes mosquitoes live | Most U.S. dengue is travel-associated |
Counts come from passive surveillance, which CDC says undercounts true infections, so treat them as minimums.
West Nile virus
CDC's West Nile page says the virus spreads mostly through the bite of an infected mosquito, that mosquitoes become infected by feeding on infected birds, and that it can also spread through blood transfusion and organ transplantation, and rarely from mother to baby. Symptoms usually begin 2 to 6 days after a bite. No licensed vaccine exists, and CDC says no medicines are available for the infection (CDC: About West Nile).
CDC's symptoms page puts it in proportions: about 80% of infected people have no symptoms, about 20% develop a flu-like illness with fever, headache, body aches and rash, and less than 1% develop severe disease affecting the central nervous system. Older adults and people with certain underlying conditions face higher risk. CDC says to seek immediate medical attention for high fever, neck stiffness, muscle weakness, confusion or tremors (CDC: West Nile symptoms).
The 2024 national report, published in MMWR on July 30, 2026, found 1,808 West Nile virus cases, 92% of all reported arboviral disease cases, below the 10-year median of 2,162. Texas (363 cases), California (103) and New York (69) accounted for 40% of neuroinvasive disease cases. The case-fatality rate among neuroinvasive cases was 13%, and 84% of West Nile cases had illness onset in July through September (MMWR, Vol. 75, No. 29). That report estimates that 40,410 to 94,290 non-neuroinvasive cases likely occurred nationally in 2024, while only 461 were reported, which is the clearest illustration of why case counts are minimums.
On 2026: a CDC statement dated July 1, 2026 reported at least 48 human cases as of June 30, 38 of them neuroinvasive, the highest count for that point in the year since 2004 (when about 10 were typical by end of June), with activity in 23 states (CDC statement). Current-year totals change weekly on CDC's West Nile data page.
Eastern equine encephalitis
CDC says EEE is passed to people mainly through the bite of an infected mosquito, that most U.S. cases occur in eastern or Gulf Coast states, and that the virus circulates in areas with freshwater hardwood swamps. Only a few cases are reported each year. Symptoms can include fever, headache, vomiting, diarrhea, seizures, behavioral changes and drowsiness. About 30% of people who develop severe illness die, and many survivors have ongoing neurologic problems. There are no vaccines or medicines for people (CDC: About EEE).
The 2024 MMWR report counted 19 EEE cases nationally, about 1% of reported arboviral disease cases. For comparison, it counted 60 Powassan virus cases (a tick-borne virus, up from a previous high of 49 in 2023), 37 La Crosse and 27 Jamestown Canyon cases. If you live near wooded swampland and want a regional plan, see mosquito and tick season by region.
Locally acquired dengue
Dengue is mainly a travel disease in the U.S., but CDC says local transmission has occurred in Florida, Texas, Hawaii, Arizona and California, and that the mosquitoes that spread it, Aedes aegypti and Aedes albopictus, live across much of the southern continental U.S. (CDC: dengue public health considerations).
In a health advisory dated March 18, 2025, CDC reported 2024 locally acquired cases in Florida (91), California (18) and Texas (1), and 3,483 travel-associated cases among U.S. travelers, an 84% increase over the previous year (CDC HAN 00523). Counts for a given year can be revised in later surveillance reports, so check CDC's dengue data page if you need a final figure. Traveling? That is a different question, covered in is lemon eucalyptus enough for travel. CDC advises preventing mosquito bites while traveling and for 3 weeks after returning, so you do not pass the virus to local mosquitoes.
What CDC says to do
CDC's guidance is consistent across these diseases: prevent mosquito bites.
- Use an EPA-registered repellent with DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol or 2-undecanone. Look for an EPA registration number. Apply sunscreen first and repellent second, and do not apply under clothing (CDC: mosquito prevention).
- Do not use OLE or PMD products on children under 3. CDC also says not to apply repellent to a child's hands, eyes, mouth, cuts or irritated skin.
- Cover up. Loose-fitting long sleeves and pants make it harder for mosquitoes to bite, and CDC's July 2026 statement advises limiting time outdoors from dusk to dawn, when the mosquitoes that spread West Nile are most active.
- Screen out mosquitoes. Use screens on windows and doors and repair holes; use air conditioning if available.
- Empty standing water weekly. Empty, scrub, turn over, cover or discard items that hold water, such as tires, buckets, pool covers and birdbaths.
Our own position is simple. We sell an aromatic oil, and a bottle of it is the wrong purchase for disease risk. Buy a registered product, read the label for the pest you care about, and put the yard and screen work first, because those reduce mosquitoes for everyone nearby. CDC says the effectiveness of non-EPA-registered repellents, including some natural ones, is unknown. For how registered OLE differs from essential oil, see oil of lemon eucalyptus vs lemon eucalyptus essential oil.
Why the season matters for planning
Timing is part of the risk. In the 2024 MMWR data, 82% of all reported arboviral disease cases had illness onset in July through September, and the CDC's 2026 statement called this West Nile season the earliest start in its records. That does not mean risk is zero in spring or late fall; it means a yard and screen check in May is cheaper than a scramble in August. Mosquito-borne disease also hits different groups differently: a majority of arboviral patients in 2024 were 60 or older (58%), while La Crosse virus disease occurred almost exclusively in children under 18 (35 of 37 cases). Parents of young children should know that CDC's OLE and PMD under-3 restriction means the product choice differs by age; ask your pediatrician which registered product fits your child.
Reading a disease number responsibly
- Year matters. Annual counts swing; CDC notes West Nile case numbers fluctuate widely because of periodic epidemics.
- Reported is not total. The MMWR estimate above shows how far apart reported and likely cases can be.
- Local numbers beat national ones. Texas, California and New York contributed 40% of West Nile neuroinvasive cases, so national averages hide regional risk. Ask your state health department.
- Neuroinvasive counts are more reliable. The MMWR authors limit incidence calculations to neuroinvasive cases because those are more consistently diagnosed and reported.
Frequently asked questions
Which mosquito-borne disease is most common in the U.S.?
West Nile virus, which CDC calls the leading cause of mosquito-borne disease in the contiguous United States. It accounted for 92% of the 2024 arboviral cases reported.
Is there a vaccine?
CDC says no licensed vaccines are available for West Nile or EEE in people. Ask your physician or a travel-medicine clinic about dengue and travel.
Does repellent matter if most infections cause no symptoms?
Yes. Severe illness is uncommon but serious, and you cannot tell in advance who will develop it. CDC says the best way to protect yourself from West Nile is to prevent mosquito bites.
Should I worry about dengue if I have not traveled?
CDC reports local transmission in several states, mainly small clusters in recent years. If you live in an affected area, follow your health department's alerts and empty standing water.
Where can I find current counts?
CDC's West Nile virus data and maps page lists current-year data, updated through summer and fall.
Lemon Eucalyptus Essential Oil
Lemon Eucalyptus Essential Oil from our own shop, in sizes from 0.5 oz to bulk.
From $9.99
Shop Now →Sources & Further Reading
- CDC: About West Nile
- CDC: West Nile symptoms, diagnosis, and care
- MMWR 2026;75(29): West Nile virus and other nationally notifiable arboviral diseases, United States, 2024
- CDC statement, July 1, 2026
- CDC: About eastern equine encephalitis
- CDC: Public health considerations for dengue
- CDC Health Advisory 00523 (March 18, 2025)
- CDC: Preventing mosquito bites