As Mosquito Season Peaks, Health Officials Prepare for a New Normal of Dengue Cases

As the summer months arrive, bringing peak mosquito activity, public health officials are preparing for a possible surge in dengue fever cases across regions where the disease is becoming more prevalent. Climate change, urbanization, and the absence of a widely available vaccine contribute to concerns that dengue may become endemic in larger parts of North America. According to recent data from the CDC, approximately 3,700 cases of dengue were reported in the United States last year, a significant increase from the previous year, with more cases being acquired locally, particularly in California, Florida, and Texas.

Dengue is traditionally endemic in tropical and subtropical regions, including Latin America, Southeast Asia, and India, with cases rising sharply in many areas last year. Historically, the United States had few local dengue cases; most infections were contracted abroad. However, recent decades have seen increased local transmission, especially in Puerto Rico, which experienced a public health emergency in 2024 due to a spike in cases.

In California, the spread of dengue is linked to the presence of Aedes aegypti and Aedes albopictus mosquitoes — vectors for the disease — which were not known to exist in the state 25 years ago. Now, these mosquitoes are found in over 400 communities across 25 counties, predominantly in Southern California and the Central Valley. The expansion of these vectors heightens the risk of disease transmission, especially as climate change fosters warmer urban environments favorable to mosquito breeding.

Most dengue infections are asymptomatic; however, symptomatic cases can include high fever, severe headaches, muscle and joint pain, bleeding, and in extreme cases, death. Diagnosing dengue can be challenging due to the lack of rapid, widely available tests. Healthcare providers are advised to consider recent travel history when diagnosing febrile illnesses.

Preventive measures include removing standing water where mosquitoes breed, using insect repellents, and avoiding outdoor activities during peak biting times at dawn and dusk. Efforts to control mosquito populations intensified after wildfires scorched parts of Los Angeles, which left many abandoned pools and other breeding sites. Local agencies are deploying various strategies, including treating stagnant water sources and exploring innovative methods like releasing sterilized mosquitoes.

Federal support for dengue and other climate-related health research appears to be waning, as the NIH reportedly plans to cut funding for new climate change studies, potentially impacting future vaccine and intervention development. Currently, vaccine options are limited: one for children is facing discontinuation due to low demand, and others are not available in the U.S.

Experts warn that without effective vaccines and antiviral treatments, dengue could establish itself as an endemic disease in the U.S. Future outbreaks remain uncertain but could become more severe with ongoing environmental changes. Researchers at institutions like the La Jolla Institute are actively working to develop more effective vaccines, aiming to reduce the disease burden.

Overall, the rising presence of dengue in the U.S. underscores the importance of vigilant mosquito control, public education, and continued research efforts to mitigate the expanding threat of this mosquito-borne disease.