West Nile virus is the leading cause of mosquito-borne illness in the continental United States. As of Sept. 23, over 1,100 human cases of West Nile disease have been reported across 42 states, according to the U.S. Centers for Disease Control and Prevention (CDC), including nearly 750 cases of the more serious neuroinvasive form which affects the brain.
CDC data show the number of cases in the United States is 40% higher than normal. Experts suggest that a warming climate is lengthening the season, which typically runs through October in the U.S. So far this season, Colorado has reported 220 cases, the highest in one state.
While most people infected with the virus do not develop symptoms, it does cause symptoms in some people, ranging from a mild, flu-like illness to a more severe illness affecting the central nervous system, which can result in hospitalization and death.
Despite this season's growing number of cases, relatively few Americans worry about becoming infected by West Nile or by dengue fever, another mosquito-borne illness, according to a survey of nearly 1,700 U.S. adults conducted August 5-18, 2025, by the Annenberg Public Policy Center (APPC) of the University of Pennsylvania. Just 15% of respondents in the nationally representative panel report being worried that they or someone in their family will contract West Nile virus or dengue fever in the next three months. This finding is unchanged from September 2024. (Read the topline .)
"With the increasing number of West Nile virus cases and a longer mosquito season, many people need to have a greater awareness of the virus and may want to consider taking everyday precautions to protect themselves from mosquito bites and control mosquitoes in and around their homes," said Ken Winneg , APPC's managing director of survey research.
Highlights
The Annenberg Public Policy Center health survey conducted Aug. 5-18 finds that:
- Just 15% of U.S. adults say they are worried about contracting West Nile virus or dengue fever in the next three months.
- Most people (75%) know that one can get West Nile or dengue fever from being bitten by an infected mosquito and the best defense against these diseases is to avoid getting bitten (81%).
- Nearly half (48%) are not sure what the symptoms of West Nile virus are.
- Knowledge of the correct way to apply mosquito repellent is low – just 14% know not to put insect repellent under your clothing and 33% know to first apply sunscreen, let it dry, and then put on insect repellent.
High knowledge about transmission; fewer know symptoms
Few people (15%) are worried that they and their families will get these diseases in the next three months, and the vast majority (85%) are unworried, no change from September 2024.
The following results show what U.S. adults know about the way West Nile virus and dengue fever are transmitted, its symptoms, how to protect themselves from mosquitoes, and what type of insect repellent the CDC recommends and how one should apply it.
Transmission: Humans usually contract West Nile virus or dengue fever through the bite of an infected mosquito. Rarely is the virus spread by person-to-person contact such as blood transfusions, breast feeding, or being sneezed or coughed on.
Most adults (75%) say scientists think that people can get West Nile virus or dengue through a mosquito bite, though 1 in 10 (11%) incorrectly say that scientists think that that form of transmission is unlikely and 14% are unsure. When asked whether scientists think someone can get West Nile virus or dengue by being sneezed or coughed on by someone with those diseases, fewer than half (43%) correctly say that is unlikely, up 9 points from September 2024. Nearly 1 in 5 people (19%) incorrectly say that scientists think an infected person coughing or sneezing on someone is a means of transmission, but that has dropped significantly since September 2024, when 26% said so. About 4 in 10 (39%) say they are unsure, no change from last year.
Treatment: There is currently no antiviral treatment for West Nile virus or dengue, but only a fifth of adults (22%) know this. Most are either unsure (61%) or believe there is an antiviral treatment (17%).
Symptoms: When presented with a list of potential symptoms of West Nile virus and asked which are symptoms of that disease, nearly half of those surveyed (48%) say they are unsure which are correct. Fever was selected by most (45%) as a symptom of the virus, followed by muscle and joint pain (41%); headache (38%); nausea and vomiting (33%); and rash (23%). Three in 10 people (31%) incorrectly chose dizziness or lightheadedness, and 12% incorrectly chose the appearance of firm, round painless sores.
Most people report taking some steps to control mosquitoes at home
The vast majority of people (81%) know the best defense against dengue fever and West Nile virus is preventing mosquito bites and controlling mosquitoes in and around their home.
Knowing this and doing something about it are two different things. Generally, 61% say they routinely take precautions to avoid getting mosquito bites, at any time of the year.
Among the group of people who say they routinely take precautions to avoid getting mosquito bites, we presented a list of specific measures asking them to indicate which ones they take. The most common measure that people choose is removing standing water (80%), followed by avoiding activities that would bring them in contact with mosquitoes (72%); wearing insect repellent (68%); replacing or repairing window screens (59%); and wearing long-sleeve or protective clothing outdoors (57%). Few (13%) say they use mosquito netting. The results are no different from September 2024.
Knowledge about how to apply mosquito repellent is low
As noted above, wearing insect repellent is one of the more common preventive measures that people report taking. But knowledge of how to properly apply mosquito repellent is relatively low, especially when dressing or applying sunscreen.
The CDC recommends that individuals do not apply insect repellent on the skin under clothing, just on exposed skin. Few people (14%) know this recommendation. Three in 10 (30%) say incorrectly that it does not matter, and about one-fifth (18%) say the CDC recommends that one apply insect repellent on the body first, then put clothing on over the areas protected by repellent. Nearly 4 in 10 (38%) say they are unsure.
When going outdoors in the day during mosquito season, it is important to apply insect repellent to prevent mosquito bites and sunscreen to protect against harmful ultraviolet rays. Just a third of adults (33%) know that the CDC recommends that one should apply sunscreen first, let it dry, then apply insect repellent. Nearly half (47%) say they are unsure, 5% incorrectly say the CDC recommends one put on the insect repellent first, followed by sunscreen, and 15% say the CDC recommends that the order of application does not matter, but that one should use both when in an area with mosquitoes, which also is incorrect.
Insect repellents can be applied to most people except babies younger than two months old. Most people know that the CDC does not recommend that insect repellent be applied to babies younger than 2 months old (54%), but 43% are not sure, and 3% believe the CDC recommends repellent for babies younger than two months.
Knowledge of how to apply insect repellent is important, but it is also important to know how to choose the safest and most effective repellent. There are many types of insect repellent available but the CDC recommends that people look for one that notes that it is EPA-registered. Only 1 in 5 (19%) adults correctly say CDC recommends using an EPA-registered repellent. A third (32%) say, incorrectly, that the CDC recommends that people look for a repellent that has over 50% of the chemical DEET. While DEET is effective as an ingredient in insect repellent, the CDC recommends using a concentration of 20-50% DEET because more than that will not usually provide extra protection against mosquito bites. The CDC does not recommend using natural repellents, though 7% of respondents believe it does and 42% are not sure.
Annenberg Science and Public Health survey
The survey data come from the 25th wave of a nationally representative panel of 1,699 U.S. adults conducted for the Annenberg Public Policy Center by SSRS , an independent market research company. Most have been empaneled since April 2021. To account for attrition, replenishment samples have been added over time using a random probability sampling design. The most recent replenishment, in September 2024, added 360 respondents to the sample. This wave of the Annenberg Science and Public Health (ASAPH) survey was fielded August 5-18, 2025. The margin of sampling error (MOE) is ± 3.5 percentage points at the 95% confidence level. All figures are rounded to the nearest whole number and may not add to 100%. Combined subcategories may not add to totals in the topline and text due to rounding.
Download the topline and the methods report .
The policy center has been tracking the American public's knowledge, beliefs, and behaviors regarding vaccination, Covid-19, flu, RSV, and other consequential health issues through this survey panel for four years. In addition to Winneg, APPC's ASAPH survey team includes research analysts Laura A. Gibson and Shawn Patterson Jr.; Patrick E. Jamieson, director of the Annenberg Health and Risk Communication Institute; and APPC director Kathleen Hall Jamieson.
See other recent Annenberg health survey news releases:
- Trust in health agencies and RFK Jr.: Public confidence in U.S. health agencies slides, fueled by declines among Democrats (Sept. 18, 2025)
- Vaccine mandates for school: Most Americans favor MMR vaccine requirements for public school (September 12, 2025)
- Health risks during pregnancy: Public knowledge high on smoking and alcohol risks during pregnancy (July 29, 2025)
- AI and health information: Many in U.S. consider AI-generated health information useful and reliable (July 14, 2025)
- Sudden infant death syndrome (SIDS): More people need to know how to prevent SIDS, survey shows (July 1, 2025)
The Annenberg Public Policy Center was established in 1993 to educate the public and policy makers about communication's role in advancing public understanding of political, science, and health issues at the local, state, and federal levels.
