First Locally Acquired Case of Dengue Under Investigation in San Diego

A female Aedes aegypti mosquito, which is the primary vector for the spread of Dengue fever. James Gathany/Centers for Disease Control and Prevention

SAN DIEGO—San Diego County health officials are investigating the first case of locally acquired dengue virus Monday from an Escondido resident who became sick with the mosquito-related disease.

The county resident who contracted the disease did not travel to an area where the virus was common. No additional locally acquired cases have been identified, although there have been at least 49 reported cases of travel- related dengue in the county this year, according to officials.

To prevent the disease from spreading, County Vector Control began spraying this weekend for mosquitoes at about 170 homes in Escondido, with treatments that began on Oct. 4 and will continue until Oct. 10, officials said in a statement from the county.

“While the risk of widespread transmission of dengue remains low in San Diego County, County Public Health and Vector Control are working closely to respond quickly to prevent mosquitoes from spreading the illness in this area,” county public health officer Dr. Ankita Kadakia said.

Vector Control did similar treatments in Oceanside in September and in the Mount Hope area of San Diego in July of this year. Both treatments were initiated as a precaution to prevent potential local spread of dengue due to travel-associated dengue cases and the high numbers of Aedes mosquitoes in the neighborhoods.

Los Angeles County recently reported five cases of locally contracted dengue this year. Long Beach and Pasadena had their first cases of locally acquired dengue in late 2023.

Dengue is a tropical viral disease that is not commonly found in the United States. Since the invasive Aedes mosquitoes were first detected in San Diego County in 2014, there had been no locally acquired cases of dengue until now.

Dengue is spread by mosquitoes when a mosquito bites an infected person and then feeds on another person.

It can take four to seven days for someone who is bitten by a mosquito infected with dengue to start feeling symptoms. Dengue can be determined by a blood test that can be discussed with a healthcare provider.

The most common symptoms are fever, chills, aches and pains, nausea, vomiting and rashes.

Symptoms can be moderate and last two to seven days. Most people recover after about a week. Symptoms can also become severe and deadly, which include shock and respiratory distress, and can require hospitalization. There are no specific medicines to treat dengue.

Day-biting Aedes aegypti mosquitoes, also known as “ankle-biters,” are the primary transmitter of dengue. These mosquitoes like to live and breed around people, often in yards and in small amounts of water.

Officials advised these tips on how to prevent and protect from mosquitoes:

• Dump out, drain, or remove any items inside and outside of homes that can hold water, such as plant saucers, rain barrels, buckets, garbage cans, toys, old tires, and wheelbarrows. Mosquitofish are available for free at locations throughout the county, and may be used to control mosquito breeding in backyard standing water sources, such as neglected swimming pools, ponds, fountains, and horse troughs;
• Protect yourself from mosquito-borne illnesses by wearing long sleeves and pants or using insect repellent when outdoors;
• Use insect repellent that contains EPA-approved ingredients like DEET, picaridin, oil of lemon eucalyptus, or IR3535;
• Make sure screens on windows and doors are in good condition and secured to keep insects out.

County technicians began working to reduce the number of adult mosquitoes that can spread dengue by applying AquaDuet, a pesticide approved for use by the Environmental Protection Agency, using ultra-low-volume backpack sprayers in focused areas and trucks to apply the product to a wider part of the area.

Additionally, the county began by informing residents and leaving door hangers at homes in the treatment area on Oct. 4. Treatment boundaries along with additional information can be found on Vector Control’s adult mosquito control webpage.

The treatment product is low-risk to people and pets and dissipates in roughly 20 to 30 minutes. People in the area can avoid or minimize their exposure to the pesticide by taking simple steps:

• Stay inside and bring pets indoors if possible;
• Close doors and windows, and turn off fans that bring outdoor air inside the home;
• Wash any pet food and water bowls that were left outside during the treatment;
• Cover fishponds to avoid direct exposure;
• Rinse fruits and vegetables from your garden with water as you normally would before cooking or eating;
• Wipe down or cover outdoor items such as toys and barbecue grills.

Beekeepers and those with insects kept outdoors were encouraged to shelter hives and habitats during treatments. Beekeepers registered with the County’s Department of Agriculture, Weights, and Measures can request to receive advance notice when a pesticide that may affect bees is applied to blossoming plants in their areas.

Normal activities may resume after 30 minutes of the treatment.

County Public Health staff will be on-site in the Escondido community Oct. 7 to answer questions and provide information about dengue.

Mosquitofish are also available for free at locations throughout the county at www.sandiegocounty.gov/content/sdc/deh/pests/wnv/services/chd_wnv_mosquito_fish_locations.html.

More information about mosquitoes can be found at San Diego County’s Fight the Bite website.