The United States is experiencing a significant surge in West Nile virus cases, with current numbers reaching the highest point in 22 years. This early and aggressive season has led to 143 reported cases nationwide as of Wednesday, a sharp increase from the average of approximately 10 cases by the end of June over the past two decades. August historically marks the peak of the West Nile virus season, and cases are expected to continue climbing.
This year's season began earlier than usual, with the most cases reported in the early summer since 2004. Of the total cases, an estimated 69% have involved an infection that spread to the nervous system, indicating a potential for severe illness.
West Nile virus, transmitted by infected mosquitos, typically causes no symptoms in about 80% of infected individuals. For those who do develop symptoms, common signs include sudden fever, fatigue, headache, muscle aches, joint pain, and gastrointestinal issues. However, a small percentage of infections can lead to serious neuroinvasive disease, requiring hospitalization. This can manifest as meningitis, an inflammation of the membranes surrounding the brain and spinal cord, or encephalitis, swelling of the brain itself. Symptoms for these severe conditions can include high fever, stiff neck, sensitivity to light, confusion, difficulty staying awake, nausea, vomiting, agitation, hallucinations, and movement changes like twitching or tremors.
In some cases, acute flaccid myelitis (AFM), a condition affecting the spinal cord and causing sudden muscle weakness, may occur alongside meningitis or encephalitis, particularly in young children. Older adults and immunocompromised individuals are at a higher risk of developing severe neuroinvasive disease.
Virus activity has been reported in 23 states, the widest spread seen in a decade. Arizona leads with 71 cases, followed by Texas with 18 and California with 11. Other states reporting fewer than five cases include Washington, Nevada, Utah, Wyoming, South Dakota, Colorado, Nebraska, New Mexico, Kansas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Florida, Tennessee, Kentucky, Virginia, and Pennsylvania. While New York has not reported human cases, infected mosquitos have been detected across the state, with nearly double the number of positive samples in New York City compared to last year as of July 25.
The West Nile virus season typically begins its ascent in May, peaks in August, and starts to decline in September, though high levels can persist until November. Public health officials recommend protective measures to prevent mosquito bites, such as wearing long sleeves and pants, using EPA-registered insect repellent, ensuring window and door screens are intact, and eliminating standing water around homes where mosquitos can breed.