West Nile virus caused the overwhelming majority of reported arboviral disease in the United States in 2024, while Powassan virus, spread by ticks rather than mosquitoes, reached its highest annual case count on record, according to a CDC surveillance report published in Morbidity and Mortality Weekly Report.
Forty-eight states and the District of Columbia reported 1,955 confirmed and probable arboviral disease cases with illness onset in 2024, including 189 deaths. West Nile accounted for 1,808 of those, or 92%. Powassan was second with 60 cases, up from the previous record of 49 reported the year before.
