Tick- and mosquito-borne viral infections claimed 189 lives across the United States in 2024, a sobering reminder that vector-borne diseases remain a persistent public health burden well beyond headline-grabbing epidemics. The 2024 national surveillance figures offer a detailed snapshot of who is most vulnerable and which pathogens are quietly expanding their foothold.
Across 48 states and the District of Columbia, 1,955 arboviral disease cases were recorded with illness onset in 2024, representing a modest dip below the ten-year median of 2,162 for West Nile virus alone. West Nile virus dominated the landscape, accounting for 1,808 cases (92% of total), with the heaviest burden falling on adults aged 60 and older, who comprised 58% of all cases, and on males (63%). The July–September window concentrated 82% of all illness onsets. More notably, Powassan virus disease reached 60 confirmed cases — surpassing its previous single-year high of 49 set just one year prior in 2023 — making it the second most reported arboviral disease nationally. La Crosse virus followed a starkly different demographic pattern, striking almost exclusively children under 18, with a median age of just 8 years.
The Powassan virus trend warrants close attention. Unlike West Nile, which spreads via Culex mosquitoes in predictable seasonal windows, Powassan is transmitted by Ixodes ticks — the same species responsible for Lyme disease — and can be transmitted in as little as 15 minutes of tick attachment, far faster than Lyme. There is no approved antiviral treatment, and neuroinvasive forms carry significant morbidity. The consecutive record-breaking years suggest either genuine range expansion, improved clinical recognition, or both. This surveillance report is observational and case-count-based, limiting causal inference, but the demographic concentration of severe outcomes in older adults aligns with known immunosenescence patterns. For health-conscious adults in tick-endemic regions, the Powassan trajectory represents one of the more underappreciated emerging infectious disease signals of the past decade.