West Nile and Dengue Cases Reach Multi-Year Highs Across U.S. This Summer
Public health officials report record-early activity of West Nile virus and a surge in locally acquired dengue cases, attributing the trends to warmer temperatures and extended mosquito seasons.
Mosquito-borne illnesses have risen sharply this summer, with West Nile virus reaching historically high levels and dengue fever cases climbing in Florida, officials said. The Centers for Disease Control and Prevention confirmed 504 West Nile infections in 41 states as of early September, including 363 neuroinvasive cases, while Florida reported 111 locally acquired dengue infections.
"We're seeing a number of mosquito-borne diseases appear more frequently or in areas where historically they have been uncommon," said Dr. Jorge Parada, medical adviser for the National Pest Management Association. He linked the uptick to warmer weather and longer mosquito activity periods, which can expand the range of vector species.
CDC data show West Nile activity began earlier than usual, with most cases recorded in August and September, marking a more than 20-year high for that time of year. The virus primarily circulates between birds and mosquitoes, with humans infected incidentally through bites. While about 80% of infections are asymptomatic, a small fraction develop severe neuroinvasive disease.
Public health experts note that the high proportion of neuroinvasive reports reflects a reporting bias, as severe cases are more likely to be diagnosed and reported than mild or asymptomatic infections.
Preventive measures emphasized by experts include using EPA-registered insect repellents, eliminating standing water around homes, and consulting pest-control professionals when mosquito problems persist.
In Florida, dengue fever cases have more than doubled compared with the previous year, all acquired locally. The disease presents flu-like symptoms, and roughly one in 20 infections can progress to dengue hemorrhagic fever, a more serious condition.
"Diseases such as dengue, chikungunya, and Zika have generated increasing concern in parts of the United States in recent years," Parada added, noting the broader risk that other eliminated mosquito-borne diseases could re-emerge as climate conditions become more favorable. He stressed the importance of mosquito surveillance, control programs, and personal protection.