WNV Remains Leading Cause of Arboviral Disease in Continental US

West Nile virus (WNV) remained the most common cause of neuroinvasive arboviral disease in the continental United States in 2021, according to findings published Aug. 25 in Morbidity and Mortality Weekly Report. The report summarizes surveillance data reported to Centers for Disease Control and Prevention by U.S. jurisdictions for nationally notifiable arboviruses (ArboNET) in 2021. It excludes cases of chikungunya, dengue, yellow fever and Zika virus because these infections were acquired primarily through travel.

In total, 49 states and the District of Columbia reported 3,035 cases of domestic arboviral disease, including those caused by WNV (2,911), La Crosse (40), Jamestown Canyon (32), Powassan (24), St. Louis encephalitis (17), unspecified California serogroup (six) and eastern equine encephalitis (five) viruses. WNV accounted for 95% of reported neuroinvasive arboviral disease cases, and the incidence of WNV neuroinvasive disease was the highest since 2012.

The researchers concluded that arboviruses continue to cause substantial morbidity in the U.S. but noted that weather, zoonotic host and vector abundance and human behavior can all influence when and where outbreaks occur. “This complexity makes it difficult to predict future locations and timing of cases and underscores the importance of surveillance to identify outbreaks quickly to direct public health prevention efforts,” the researchers wrote.