Arthropod-borne viruses (arboviruses) are transmitted in the United States primarily through infected ticks or mosquitoes. The data for national reportable domestic arboviral illnesses for the year 2023 are compiled in this report. The District of Columbia and 48 states reported a total of 2,770 cases of human arboviral illness, including 208 deaths and 2,022 hospitalizations. A total of 2,628 of all reported cases were shown to have West Nile virus (WNV), which is considered the most prevalent domestic arboviral disease.
In 2023, there were three documented incidences of WNV illness in patients who had received organ transplants from two donors. The transmission cycles of arthropod-borne viruses continue between arthropods and vertebrate hosts such as humans and other animals. The WNV is the most common arboviral disease in the U.S., accounting for 2,000 cases per year, of which 1,200 cases are neurological disorders that are fatal, and around 120 cases are reported as fatalities. To detect trend and discrepancies, patient demographics and case characteristics were compared using data submitted to ArboNET, the national arboviral surveillance system.
State health departments voluntarily report cases of the six nationally notifiable arboviral diseases to the CDC through ArboNET, using a uniform case definition. In 2023, Powassan virus disease was the most frequently reported since it became a distinct reportable condition in 2004, with 49 cases from 11 states. Additionally, 21 cases of St. Louis encephalitis virus disease were reported from three states, including California, which documented its first-ever human case.
To learn more about the new lineage, surveillance for infected vectors and incidences of illness in humans and animals is required. Physicians should think about testing for arboviral disease in patients presenting with severe fever or neurological condition, including those with recent organ transplants or blood transfusions. In the US, all 48 states and the District of Columbia reported 772 of the 3,143 cases. Around 63% of cases were in men, and over 57% of reported cases were patients aged ≥60 years.
In 2023, four states reported seven cases of eastern equine encephalitis virus disease, which is equal to the median number of cases reported between 2003 and 2022. Variations in the ecology and vectors used to transmit arboviruses are partially reflected in variations in the timing of their transmission. The occurrence of disease is impacted by weather changes that encourage the growth of vector populations or animal hosts. For every incidence of WNV neuroinvasive disease, there may be 30 to 70 cases of non-neuroinvasive cases, many of which go unreported. For instance, during the 2021 WNV outbreak in Arizona, the overall number of arboviral disease cases doubled compared to 2022.
To findings underscore the ongoing need for robust surveillance efforts to guide public health responses and preventive measures. This study highlighted that the risks during solid organ transplantation were associated with high rates of morbidity and mortality. The importance of screening organ donors for viral WNV RNA to prevent inadvertent transmission.
Reference: Padda H, Jacobs D, Gould CV, et al. West Nile virus and other nationally notifiable arboviral diseases—United States, 2023. MMWR Morb Mortal Wkly Rep. 2025;74(21):358-364. doi:10.15585/mmwr.mm7421a1
