Dengue Fever: Officials Warn of Increasing Cases Amid Mosquito Season

As the summer season reaches its peak, health and vector control officials across the United States are preparing for a significant rise in dengue fever cases. The Centers for Disease Control and Prevention (CDC) reported approximately 3,700 new dengue infections in 2024, a marked increase from about 2,050 cases in 2023. This rise is largely attributed to environmental factors, the spread of Aedes mosquitoes, and the ongoing challenges in vaccine development and public health funding.

Dengue fever, a viral illness transmitted by the Aedes aegypti and Aedes albopictus mosquitoes, has been historically rare in the contiguous United States. However, health experts, including Dr. Michael Ben-Aderet, associate medical director of hospital epidemiology at Cedars-Sinai in Los Angeles, suggest that the disease is likely to become endemic in the region. "Dengue is here with us to stay," Dr. Ben-Aderet stated, emphasizing the persistence of these mosquitoes in urban settings where they thrive.

The CDC's health alert issued in March underscored the persistent threat posed by dengue, particularly following a public health emergency declared in Puerto Rico due to a surge in cases. While most dengue infections do not result in severe symptoms, the disease can lead to serious complications, including hemorrhagic fever and even death in some cases.

California serves as a notable case study for the spread of dengue within the U.S. Historically, the Aedes mosquitoes were not present in the state, but they have now been identified in 25 counties and over 400 cities, predominantly in Southern California and the Central Valley. From 2016 to 2022, California reported an average of 136 new dengue cases annually, primarily from travelers returning with the virus. However, in 2023, the state saw a significant spike, with 250 new cases, including two locally acquired infections. This trend escalated further in 2024, with 725 cases reported, 18 of which were contracted locally.

Climate change is cited as a contributing factor to the increase in Aedes mosquito populations. These mosquitoes thrive in warmer climates, often biting during the day, which increases the likelihood of disease transmission. Dr. Ben-Aderet noted, "They’ve just been spreading like wildfire throughout California," highlighting the urgent need for public health interventions.

Efforts to combat dengue are complicated by limited funding for vector control programs. Local agencies, often funded by property taxes, face challenges in managing mosquito populations, especially following natural disasters like wildfires that create ideal breeding conditions. For instance, the San Gabriel Valley Mosquito and Vector Control District has been working to treat over 1,400 neglected swimming pools after fires in the area. District spokesperson Anais Medina Diaz mentioned that they have sought reimbursement from the Federal Emergency Management Agency for these efforts, though such funding has historically been sparse for vector control initiatives.

Innovative strategies are being proposed, including the release of sterilized Aedes mosquitoes to reduce populations. However, as Steve Abshier, president of the Mosquito and Vector Control Association of California, points out, this approach would require substantial funding and coordination at the state level to be effective.

The federal landscape for public health funding is also shifting, with reports indicating that the National Institutes of Health plans to cease funding new research related to climate change, which could hinder ongoing efforts to understand and control dengue.

While reported dengue cases in much of the Americas have declined in 2025, experts remain uncertain about the situation in the United States. Sujan Shresta, a professor at the La Jolla Institute for Immunology, notes that countries like Nepal have experienced similar shifts in dengue trends, moving from few cases to significant outbreaks. Shresta's research team is working on developing an effective vaccine for dengue, with hopes of initiating human trials following promising results from animal testing.

As summer progresses, health officials advise the public to take preventive measures against mosquito bites, including eliminating standing water around properties and using insect repellent. The potential for dengue to become a regular public health concern in the U.S. necessitates urgent attention and action from both local and federal health authorities.