CDC’s recent ArboNET snapshot shows widespread human and non-human activity, preliminary totals subject to change, and no lineage reporting on the dashboard.
West Nile virus human disease cases reported by state of residence, 2025
Image credits: CDC
As of September 9, 2025, CDC’s ArboNET reports 771 human West Nile virus cases across 39 states, including 490 neuroinvasive (severe) cases. These figures are preliminary and typically update every one to two weeks. Officials note this season is tracking higher than usual for early September, and the peak risk window is not yet over.
Widespread non-human activity in mosquitoes, birds, and sentinel animals signals ongoing transmission. Some jurisdictions report only at the state level, and presumptive viremic blood donors can appear in totals even if they had no symptoms at donation.
Interpreting ArboNET requires caution. Mild, non-neuroinvasive illness is often underreported, reporting lags are common, cases are assigned by county of residence rather than exposure location, and non-human surveillance varies by jurisdiction. These factors limit location-to-location and week-to-week comparisons.
West Nile virus remains the leading mosquito-borne disease in the contiguous United States, with transmission peaking from late summer into early fall. Most infections are asymptomatic or mild, but a subset progress to severe neuroinvasive disease, with higher risk among older adults and people with certain chronic conditions. There is no licensed human vaccine or specific antiviral treatment, so prevention focuses on avoiding mosquito bites, using EPA-registered repellents, and removing standing water.
West Nile virus totals reached 771 human cases with reports from 39 states as of Sept 9, 2025.
Severe disease remains substantial with 490 neuroinvasive cases, highlighting ongoing clinical and public health impact.
ArboNET data have known limits, including underreporting, reporting lags, county-of-residence assignment, variable non-human surveillance, and no routine lineage breakdo
In June, CDC Epidemic Intelligence Service officer Hannah Padda, DVM, MPH, told Contagion that the United States recorded 2,770 nationally notifiable arboviral cases in 2023, 95% due to West Nile, resulting in more than 2,000 hospitalizations and 208 deaths. She also highlighted the first US human infection involving West Nile lineage 3 (L3), detected alongside the common lineage 1, which exposed gaps because routine diagnostics do not distinguish lineages. The CDC documented three transplant-related West Nile transmissions in 2023, underscoring the need for vigilant donor screening. Padda added that Powassan reached a new case high and that La Crosse virus remains the top cause of pediatric neuroinvasive arboviral disease, reinforcing calls for enhanced detection, clinician awareness, and vector control. The 2025 ArboNET dashboard does not include lineage reporting.
ArboNET totals will continue to update through the fall, and the dashboard does not include lineage details. For now, the guidance is unchanged: use EPA-registered repellents, reduce standing water, and clinicians should consider testing and report suspected cases.
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