KFF Health News’s Phillip Reese
Health and vector control experts are preparing for the prospect of another year with record-breaking dengue rates as summer brings in peak mosquito season. Additionally, they fear the disease will spread to a wider region of North America due to climate change, the lack of a viable vaccine, and federal research cuts.
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According to the Centers for Disease Control and Prevention, there were approximately 3,700 new dengue illnesses in the contiguous United States last year, compared to roughly 2,050 in 2023. With the exception of 105 instances that were contracted in California, Florida, or Texas, every case from the previous year was acquired overseas. In March, the CDC released a health advisory alerting people to the continued risk of contracting dengue.
Michael Ben-Aderet, an infectious disease specialist and associate medical director of hospital epidemiology at Cedars-Sinai in Los Angeles, stated that he believes dengue is here to stay and will become the new normal in the United States. These mosquitoes are here to stay.
Health professionals use the term “endemic” to describe dengue when the disease is seen in many warmer regions of the world, such as Southeast Asia, India, and Latin America, on a regular basis. In several of those locations, particularly in Central and South America, dengue cases significantly climbed last year.
For a large portion of the previous century, the disease was uncommon in the contiguous United States. It can spread when people are bitten by an infected Aedes mosquito. Puerto Rico now accounts for the majority of locally acquired (i.e., unrelated to travel) dengue cases in the United States. In 2024, the number of cases increased significantly, leading to a local public health emergency.
The majority of dengue patients become ill. However, some patients experience severe symptoms, such as vomiting, swelling, extreme stomach discomfort, and bleeding from the mouth or nose. Dengue can sometimes be fatal.
California is an example of the expansion of dengue in the United States. Twenty-five years ago, the state was unknown to harbor the dengue-transmitting Aedes aegypti and Aedes albopictus mosquitoes. Today, primarily in Southern California and the Central Valley, they can be found in 25 counties, as well as over 400 cities and unincorporated towns.
According to Steve Abshier, president of the California Mosquito and Vector Control Association, the spread of the mosquitoes is alarming since their presence raises the risk of disease transmission.
California saw an average of 136 new dengue cases annually from 2016 to 2022; each case was probably brought to the state by a visitor who had contracted the virus somewhere else. About 250 new cases were reported in 2023, including two that were obtained locally.
According to state records, there were 725 new cases of dengue in California in 2024, 18 of which were acquired locally.
According to Ben-Aderet, the number of Aedes mosquitoes may increase as a result of climate change. These mosquitoes typically bite throughout the day and thrive in warm metropolitan environments. When someone contracts dengue while traveling and returns home, they are frequently bitten by an Aedes mosquito that spreads the sickness to another person. This is known as a locally acquired infection.
According to Ben-Aderet, they have been sweeping over California like wildfire.
For many primary care physicians who have never seen dengue, it is a challenge. Ben-Aderet stated that although it is not always easy to establish the diagnosis, physicians who suspect dengue should ask their patients about their travel history.
He stated that there is no simple test for it. Antibody testing are our only method of diagnosing dengue. He went on to say that most laboratories probably don’t do it for a living, therefore it’s typically a send-out test. Therefore, you must have a strong suspicion that someone has dengue.
According to Abshier, employing insect repellent and removing any standing water, even little ones, from a property are the best ways to prevent dengue. Reducing activity during the times when mosquitoes bite the most, which are dusk and dawn, can also be beneficial.
California’s efforts to fight dengue were made considerably more difficult this year as wildfires tore across Los Angeles. The fires happened in an area where mosquito-borne diseases are common. Officials from the San Gabriel Valley Mosquito and Vector Control District have spent months treating over 1,400 neglected swimming pools that were left behind after the fire, eliminating possible mosquito breeding grounds.
According to district spokesman Anais Medina Diaz, San Gabriel vector control personnel have treated the pools using both state and municipal resources. The Federal Emergency Management Agency, which has not previously covered vector control expenses after wildfires, has received their application for payment.
In California, local taxes and property owner fees are frequently the main source of funding for vector control organizations.
To lessen the issue, some authorities are attempting the innovative strategy of releasing sterilized Aedes insects. That might work, but it would be expensive and take a lot of work at the state level to implement the strategy in many places, Abshier said. The federal government is reducing its interventions in the interim: According to a number of sources, the National Institutes of Health will no longer support new research on dengue and other climate change-related topics.
In several parts of the Americas, recorded dengue incidence have drastically decreased from 2024 to this year. However, it is unlikely that the U.S. tendency will become evident until the end of the summer mosquito season later in the year.
Researchers studying vector management and health are unsure of how severe it will develop in California. While some think dengue might get much worse, others say outbreaks may be restricted.Other regions, such as Nepal, had relatively few dengue cases in the recent past but now frequently have significant outbreaks, according to Sujan Shresta, a professor and infectious disease researcher at the La Jolla Institute for Immunology.
A childhood vaccine exists, however it is being discontinued due to a lack of demand worldwide. The United States does not have access to two other dengue vaccines. Shresta’s lab is working diligently to develop a safe and effective dengue vaccine. In a year or so, she expects to make the results of animal research public; if they are favorable, human trials would be feasible in two years.
According to her, this country will become endemic for dengue if there is no effective vaccine or antiviral medication.
Phillip Reese is an associate professor of journalism at California State University-Sacramento and an expert in data reporting.
The California Health Care Foundation’s editorially independent service, California Healthline, is published by KFF Health News, which also produced this item.
(One of the main projects of KFF, the independent source for health policy research, polling, and journalism, is KFF Health News, a nationwide newsroom that delivers in-depth journalism about health issues.)
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