West Nile Virus and Other Nationally Notifiable Arboviral Diseases — United States, 2024

In the United States, arthropodborne viruses (arboviruses) are primarily transmitted by infected mosquitoes or ticks; rarely, they can be transmitted through blood transfusion or organ transplantation. Whereas a majority of arboviral infections are asymptomatic, symptomatic infections range from mild febrile illness to severe neuroinvasive disease. This report summarizes data for nationally notifiable domestic arboviral diseases with illness onset in 2024. Forty-eight states and the District of Columbia reported 1,955 arboviral disease cases, including 189 (10%) deaths. Although the number of West Nile virus (WNV) disease cases in 2024 was below the 10-year median (2,162), WNV caused most reported arboviral disease cases (1,808; 92%). Powassan virus disease was the second most commonly reported arboviral disease (60; 3%), increasing from a previous high of 49 cases in 2023. A majority of patients with arboviral disease were aged ≥60 years (1,133; 58%), were male (1,223; 63%), and had illness onset during July-September (1,603; 82%). However, La Crosse virus disease occurred almost exclusively among children aged <18 years (35 of 37 cases; median age = 8 years; interquartile interval = 5-10 years). Variations in annual demographic characteristics, disease incidence, distribution, and seasonal temporality of arboviral diseases highlight the importance of quality and -timely surveillance to increase awareness of disease risk, facilitate testing, and implement control measures. Clinicians should consider arboviral testing for patients with acute febrile or neurologic illness during periods when mosquitoes and ticks are active. Reducing arboviral disease morbidity and mortality relies on use of personal protective measures (e.g., insect repellent and protective clothing), implementing vector-control activities, and screening blood and organ donors for WNV.