The Los Angeles County Department of Public Health is investigating the first case of locally acquired dengue for the 2025 mosquito season in a resident of the San Gabriel Valley.

The person reported no history of travel to areas where dengue is endemic. The individual developed symptoms in late September and is recovering. While the potential risk for widespread dengue virus transmission in Los Angeles County remains low, this case highlights the presence of infected mosquitoes locally and underscores the importance of preventive measures to control the spread of this virus.

Public Health’s first confirmed case of locally acquired dengue was reported Sept. 9, 2024. During the 2024 mosquito season, L.A. County saw an emergence of locally acquired dengue, reporting a total of 14 cases, which is extremely rare for a region where the virus had not previously been transmitted by mosquitoes.

Dengue is transmitted primarily through the bite of infected Aedes mosquitoes. It can take 5-7 days for a person to develop symptoms after being bitten by a mosquito infected with dengue. Persons infected with dengue may have flu-like symptoms including high fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and mild bleeding. Severe dengue can result in shock, severe bleeding and severe organ impairment which require immediate medical attention. Residents who have symptoms of dengue should see their healthcare provider. A blood test is the only way to confirm dengue infection.

“Dengue is preventable, and community action is our strongest defense. Preventing mosquito bites and mosquito breeding is the best way stop local transmission of dengue,” said Muntu Davis, MD, MPH, Los Angeles County Health Officer. People should follow these simple steps to reduce their exposure to mosquitoes and risk for mosquito bites: 1) Use insect repellent on you and your family; 2) Remove items that hold standing water around your home where mosquitoes can lay eggs and breed; and 3) Use, install, or repair window and door screens to prevent mosquitoes from entering your home.”

Public Health urges healthcare providers to consider dengue in patients with acute febrile illness and test for and report suspect cases of mosquito-borne diseases. Providers should also routinely discuss mosquito bite prevention with patients and travelers.

Public Health is working closely with the San Gabriel Mosquito and Vector Control District on enhanced surveillance, response measures and active engagement with the community. The SGVMVCD is trapping and monitoring mosquitoes and taking steps to reduce their population to reduce further spread in the neighborhood.

“In response to emerging disease risk, the District rapidly launched enhanced mosquito control operations across the community,” said SGVMVCD District Manager Jason Farned. “Teams are actively conducting surveillance, eliminating breeding sources, and engaging residents to reduce the risk of further transmission. We encourage residents to take simple preventive steps at home, like tipping out standing water and using mosquito repellent.”

Everyone in LA County can take proactive steps to reduce mosquito breeding, avoid mosquito bites, and prevent the ongoing local transmission of dengue. This includes:

-Wearing Mosquito Repellent: Mosquito repellents can keep mosquitoes prevent mosquito bites. EPA-registered repellents containing DEET, picaridin, IR3535, 2-undecanone, and oil of lemon eucalyptus are the longest lasting and most effective. They are available as sprays, wipes, and lotions. Consider wearing long-sleeved clothes and pants when outside.

-Keeping mosquitoes out their homes: Make sure that doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.

-Preventing mosquito breeding: Eliminate standing water where mosquitoes can lay eggs.

*Clear standing water in flowerpots, saucers, birdbaths and other outdoor containers. Empty items that hold water inside and outside your home once a week. Mosquito eggs only need a thimbleful of water to hatch.

*Cover water storage containers such as buckets and rain barrels. For containers with no lid, use wire mesh with holes smaller than an adult mosquito.

*Clean and maintain swimming pools, spas and drain water from pool covers.

*Throw away old items in your patio or yard that can hold water, e.g., old car tires and children’s toys.

*Call 2-1-1 or your local vector control agency to report persistent problems to your mosquito control district

About Dengue

Dengue is a disease caused by a virus that spreads through the bite of an infected mosquito. Dengue is common in tropical and subtropical regions such as the Caribbean (including Puerto Rico), Central and South America, Southeast Asia, and the Pacific islands. Because the types of mosquitoes that spread dengue are common throughout many areas of the United States, local spread of dengue can occur. However, dengue is not commonly spread by mosquitoes in LA County. Most cases in LA County have been identified among those who have traveled to areas where dengue commonly occurs.

Symptoms of dengue typically last two to seven days. Most people will recover after about a week. About one in twenty people with dengue can develop severe disease which can be life threatening.

The most common symptoms of dengue are fever and one or more of the following:

-Eye pain

-Headache

-Muscle, bone or joint pain

-Nausea or vomiting

-Rash

There are no specific medicines to treat dengue. There are supportive medicines to help with fever and pain. There is a vaccine for dengue, but it is NOT approved for use in U.S. travelers who are visiting but not living in an area where dengue is common.

For more information, visit: ph.lacounty.gov/dengue

For questions or to find a nearby clinic or doctor, call the Public Health InfoLine at 1-833-540-0473, open every day from 8 a.m. to 8 p.m.