Mosquito-borne illnesses increasing in US. See map of affected states

Mosquito-borne illnesses increasing in US. See map of affected states.

Key points

• 8, the CDC has confirmed 504 total cases of West Nile in 41 states.
• While 20% develop a flu-like illness that resolves without medical intervention, the CDC estimates that only 1% of those who contract West Nile experience severe neuroinvasive disease.
• The CDC remarked in a July 1 notice that numbers represented a more than 20-year high for that time of year.
• Most mosquitoes don't carry West Nile, and the average American who is bitten is unlikely to obtain sick, Parada stated.
• Products containing DEET, picaridin, oil of lemon eucalyptus, para-menthane-diol and IR3535 have all been shown to be effective when applied according to label directions.

Mosquito-borne illnesses increasing in US. See map of affected states. Mary Walrath-Holdridge USA TODAY. Leading symptoms of West Nile Virus, explained.

West Nile Virus is the leading cause of mosquito-borne diseases in the U.S., with the highest concentration in the Midwest. Here's how to tell if you're infected.

As Western states fight a rise in West Nile virus and the South contends with a surge in dengue fever, mosquito-borne diseases have left some Americans uneasy as this summer season comes to a close.

While some mosquito-borne illnesses common in more tropical climates, such as malaria and yellow fever, have been absent from the mainland U.S. For a number of years, numerous others remain present and are gaining ground stateside. An especially active West Nile season, for example, has prompted multiple state and federal agencies to matter public warnings.

"We're seeing a number of mosquito-borne diseases appear more frequently or in areas where historically they have been uncommon, " Dr. Jorge Parada, medical adviser for the National Pest Management Association, informed USA TODAY. "Warmer temperatures and longer mosquito seasons can expand the range of certain mosquito species and increase the amount of time they remain active each year."

As warming weather and an increasingly favorable climate allow pests to live longer and travel further, this year's exceptionally active tick season can be attributed to similar culprits, experts previously informed USA TODAY.

Even in one of the most biodiverse forests on Earth, mosquitoes are increasingly finding humans on the menu, according to multiple studies conducted in Brazil. Researchers say habitat changes and growing human presence may be making individuals an easier target than wildlife, potentially increasing opportunities for mosquito-borne diseases to jump between animals and humans. Here's what to know. West Nile is trending historically high.

West Nile cases began picking up earlier this year, with the vast majority recorded in August and September, according to historical Centers for Disease Control and Prevention (CDC) data. The CDC remarked in a July 1 notice that numbers represented a more than 20-year high for that time of year.

"West Nile virus is more prominent this year. National surveillance data from the CDC demonstrates that the season secured off to a historically early and active start, " Parada noted. "The virus appears to have surged earlier in the spring and summer than we typically see, which is likely driven in part by warm weather and active mosquito populations."

West Nile is primarily a mosquito-bird disease, with humans being an incidental host, Parada remarked. This means mosquitoes obtain it from infected birds, and residents then obtain it when bitten by mosquitoes. When more birds have the virus, more mosquitoes carry it as well.

Warmer weather that comes earlier and lasts longer enables more mosquitoes to live and bite more individuals. Additionally, natural cycles in the bird population play a role in year-to-year transmission, Parada explained.

"Because West Nile can be fatal to birds, periods of heavy transmission may eventually reduce the number of infected birds available to sustain the cycle, " he remarked. "Over time, new generations of birds that have never been exposed to the virus become susceptible, creating conditions for transmission to increase again."

As of Sept. 8, the CDC has confirmed 504 total cases of West Nile in 41 states. A sizeable portion, 363, of those were neuroinvasive disease cases: a severe form of the illness associated with high mortality and disability that occurs when the virus spreads to the central nervous system.

While 20% develop a flu-like illness that resolves without medical intervention, the CDC estimates that only 1% of those who contract West Nile experience severe neuroinvasive disease. The majority, or roughly 80%, do not develop any symptoms or apparent illness.

For context, the good news: The sizeable percentage of U.S. Cases categorized as neuroinvasive West Nile virus doesn't necessarily mean more residents who contract the illness are getting sicker. Instead, it's an anomaly of how we track and report infectious disease in the United States.

"This is most likely due to a diagnosis and reporting bias, rather than a sudden change in the virus itself, " Parada remarked. "Most individuals infected with West Nile virus never develop symptoms, so they don't seek medical care and are never officially diagnosed. By contrast, patients who develop severe neurologic symptoms are much more probable to be hospitalized and secure tested." Symptoms of West Nile.

Most mosquitoes don't carry West Nile, and the average American who is bitten is unlikely to obtain sick, Parada stated. Regarding 80% of residents don't develop symptoms, and most who do experience what's known as "West Nile fever, " a flu-like illness that can cause fever, headache, body aches, fatigue, nausea, vomiting, diarrhea, rash or swollen lymph nodes.

In the rare neuroinvasive cases, the virus can affect the central nervous system and cause serious conditions such as meningitis or encephalitis. Symptoms may include high fever, stiff neck, confusion, disorientation, muscle weakness, numbness, paralysis, vision loss, coma or even death.

As with other infectious diseases, individuals most at risk include older adults (especially over 60), those with weakened immune systems, and individuals with chronic underlying medical conditions such as cancer, diabetes or chronic kidney disease.

Prevention is the best tool in fighting West Nile, remarked Parada. This person suggests the after.

Employ EPA-registered insect repellent. Products containing DEET, picaridin, oil of lemon eucalyptus, para-menthane-diol and IR3535 have all been shown to be effective when applied according to label directions.

Mosquitoes can breed in as little as half an inch of standing water, so remove water around your property. That means regularly emptying water from flowerpots, birdbaths, buckets, tires, toys, pet bowls and other containers. Don't forget to check and clean gutters. It are a commonly overlooked source of standing water.

If mosquitoes are becoming a persistent difficulty, contact a qualified pest control professional. They can support identify potential breeding sites and recommend a targeted management plan. Dengue fever and other mosquito-borne illnesses.

While West Nile is making "historic" headlines, other mosquito-borne illnesses have seen surges in the United States this season.

Dengue fever spiked in Florida lately, totaling 111 cases as of Sept. 5. All of those cases were locally acquired, meaning individuals caught it in Florida, not while traveling abroad. The rise is compared with 2025, during which 62 individuals tested positive in total.

Like West Nile, the symptoms are generally flu-like, including aches and pains, nausea, vomiting and rash. Regarding 1 in 20 residents who contract dengue develop a more serious illness called hemorrhagic fever, according to the CDC. It can entail symptoms like abdominal pain, frequent vomiting, bleeding from the nose or gums and blood in stool or vomit.

"Diseases such as dengue, chikungunya, and Zika have generated increasing concern in parts of the United States in recent years, " Parada remarked. "Looking ahead, one of the concerns among public health experts is whether mosquito-borne diseases that were once eliminated from the U.S., such as malaria, could eventually gain a foothold in areas where environmental conditions become more favorable."

He continued: "All of this underscores the importance of mosquito surveillance, mosquito control programs, and personal protection measures." Share your feedback to assist improve our site!

For now, mosquito-borne illnesses increasing in US. See map of affected states remains the part of the story worth watching, and further updates are likely as more details are confirmed.