West Nile virus is appearing unusually early across the United States this year, prompting health officials to urge residents to take precautions as mosquito activity builds toward its late-summer peak.
On July 1, the Centers for Disease Control and Prevention (CDC) confirmed that 48 West Nile cases had been reported nationwide as of June 30, nearly five times the average for that point in the season. Of those cases, 38 escalated to neuroinvasive disease, a severe form of the illness that affects the brain and spinal cord.
By July 14, provisional CDC data showed a surge to 81 total infections, 57 of which were neuroinvasive. Virus activity has been reported in 23 states: the highest number at this point in the season in at least a decade.
The CDC officially attributed the surge to an “unusually early circulation of the virus,” but scientists at Stanford University and the New York Department of Health agree that climate change is a contributing factor.. Rising temperatures and changing rainfall patterns can increase mosquito populations and make it easier for them to spread pathogens, including West Nile virus.
New York health officials issued their own warning on July 15 after West Nile virus was detected in mosquitoes in Nassau, Rockland, and Suffolk counties. Over the past decade, the state has recorded 569 human cases and 30 deaths from the virus.
West Nile virus is the leading cause of mosquito-borne disease in the contiguous United States. First detected in New York City in 1999, it has since been reported in all 50 states. From 1999 through 2025, more than 63,000 cases and 3,300 deaths were reported nationwide.
These confirmed diagnoses represent only a fraction of the true toll. Because about 80% of infections cause no symptoms and therefore go unreported, researchers estimate that the actual number of cases is more than 130 times higher than official statistics suggest. The total number of deaths may also be 33% higher because of overlooked long-term complications.
First discovered in Uganda’s West Nile district in 1937, the virus circulates primarily between birds and mosquitoes. Mosquitoes become infected when they feed on infected birds and can then transmit the virus to people and other mammals through their bites.
Horses are particularly vulnerable, but effective equine vaccines are available. No vaccine has been licensed for humans.
Infected people usually develop flu-like symptoms within seven days after a bite, such as fever, joint pain, and headache. The illness generally resolves in a week, although fatigue and muscle pain can linger for months.
In about 1 in 150 West Nile cases, the virus spreads to the central nervous system, and can result in seizures, paralysis, coma, or death. Those who recover from these severe neurological complications are often left with permanent disabilities.
Those at highest risk for severe disease include anyone over the age of 60, or those with chronic disease, like hypertension, diabetes, or cancer.
There is no specific antiviral treatment or cure for West Nile infection, but mild symptoms can be managed with proper hydration and over-the-counter medication like acetaminophen for fever and body aches. Individuals who contract the virus are believed to gain lifelong immunity.
If you suspect an infection, contact your health care provider, who can confirm the diagnosis with an antibody blood test. Severe neurological symptoms—such as high fever (103° or greater), severe headache, or confusion — require immediate medical attention. If you experience any of these warning signs, call 911 or go to the nearest emergency room.
The best protection against West Nile virus is to avoid mosquito bites.
- Minimize outdoor activities at dawn and dusk, when mosquitoes are the most active.
- Wear lightweight long pants and a long-sleeved shirt outdoors.
- Consider applying an insect repellent to exposed skin. Choose a product containing 20-30% DEET, and follow label directions.
Control mosquitoes in and around your home.
- Make sure all windows and doors have intact mesh screens.
- At least once a week, empty and scrub out any items that hold stagnant water, including vases, birdbaths, and baby pools.
- Keep lids on rain barrels, trash cans, and recycling bins. (Private homeowners rarely need to use pesticides if standing water is properly managed.)
Wide-scale chemical spraying to control West Nile virus has never been authorized in Dutchess or Columbia counties, although larvicide briquettes have been used in infested stagnant water.
The New York State Department of Health works closely with all counties to monitor mosquitoes by trapping and testing the insects, and tracking dead bird reports. If you find a cluster of dead birds, don’t touch them or let your pets near them. Contact the New York State Department of Environmental Conservation at 518-478-2203, or complete their online form. The birds will also be checked for avian flu.
Dr. Mary Jenkins, a contributor to the Herald and member of its board of directors, retired after nearly 40 years as a family practice physician in New York state.