Palm Beach and Miami-Dade health officials issued alerts Monday to increase personal mosquito protection after locally transmitted dengue fever cases were confirmed in both counties.

Dengue fever is transmitted by the same type of daytime-biting mosquito that spreads other viral infections, including chikungunya. This is peak season for dengue cases, with July through September the highest-risk window of the year.

Those prone to mosquito bites, beware of symptoms such as high fever accompanied by severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen glands, and a skin rash.

Along with issuing an advisory, the Florida Department of Health Palm Beach and Palm Beach County Mosquito Control are coordinating prevention efforts. South Florida counties are doing larvicide spraying in areas to reduce the number of mosquito-breeding habitats

Despite mosquito-control efforts, South Florida had one of the highest counts of dengue cases in the country in 2025. Florida remains the highest-risk state for locally acquired dengue in the continental United States — with about 50 cases reported through July, according to the Centers for Disease Control and Prevention. Nationwide, dengue fever has surpassed 500 cases in 2026, following a record-breaking 2024 that saw 3,798 confirmed cases reported to the CDC’s ArboNET surveillance system

Researchers at The University of Florida’s Emerging Pathogens Institute have linked the abundance of Aedes aegypti mosquitoes in Florida to conditions like high temperatures and lots of rain, which have enabled more frequent local transmission of dengue and chikungunya.  The majority of dengue fever cases remain travel-associated and most often acquired in the Caribbean, Central America, or Mexico. However, returning travelers are seeding the virus into areas with large mosquito populations, according to the CDC.

Dengue fever spreads through mosquito bites, not from person to person through bodily fluids or contact. Most people recover within one to two weeks. Severe dengue, more likely in people experiencing a second infection, can cause bleeding under the skin, gum or nose bleeds, blood in urine or stool, persistent vomiting, abdominal pain, rapid breathing, fatigue and restlessness.

Disease experts say DEET remains one of the most effective preventive measures against mosquitoes and should be reapplied often when outside this time of year.

There is more reason to wear mosquito protection: The CDC is seeing the earliest start to the West Nile virus season in the United States, with the highest number of human disease cases reported by this time of year since 2004.

South Florida Sun Sentinel health reporter Cindy Goodman can be reached at cgoodman@sunsentinel.com.