The Centers for Disease Control and Prevention is warning travelers about dengue fever, a mosquito-borne virus that can cause serious illness.

Last Tuesday, the agency released a health alert announcing that dengue rates are high in the Americas. Over 760,000 dengue cases were reported in the region this year, a 15% increase from the average rate of the past five years.

The CDC alert also warned that dengue fever is especially high in Puerto Rico and the U.S. Virgin Islands, popular spring break destinations.

Puerto Rico has seen 936 cases in 2025—a 113% increase compared to the same period in 2024—and has been in a state of public health emergency since last March. There have been 30 dengue cases reported in the U.S. Virgin Islands this year. In 2024, dengue outbreaks were declared in both territories, which remain in effect.

Dengue fever has also been reported in the continental U.S. this year, including six cases in New York, 10 in California, and 45 in Florida.

“The reason that it’s always a problem this time of year is that a lot of people travel to warmer climates this time of year, and therefore, the risk of infection is higher,” Rebecca Schein, MD, a board-certified pediatrician who specializes in infectious diseases and an assistant professor at the College of Human Medicine at Michigan State University, told Health.

Here’s what you need to know about dengue fever—plus, how to protect yourself if you’re traveling to a dengue hotspot.

Dengue fever is a common disease spread by mosquitoes carrying the dengue virus. Millions of dengue cases are reported worldwide each year, and the disease is especially prevalent in tropical and subtropical climates with more mosquitoes.

Dengue fever can cause serious illness, which is sometimes fatal. In 2024, there were 13 million cases and 8,200 deaths from dengue in the Americas.

One in four people with dengue fever will have symptoms, typically lasting two to seven days. Symptoms can develop up to two weeks after the infected mosquito bite. 

According to the CDC, the most common symptom of the infection is fever, accompanied by:

• Aches and pains, typically behind the eyes and in the muscles, joints, or bones
• Nausea and vomiting
• Rash

About one in 20 people who are sick with dengue fever will have a severe infection. Some groups are more susceptible to severe illness: infants, pregnant women, adults aged 65 and older, people with weakened immune systems, and people who have previously had dengue fever.

Many times, catching a virus once allows your body to build up immunity if you encounter it again—but that’s not exactly the case with dengue, Ana Maria Bensaci, MD, MPH, an infectious disease physician at Tufts Medical Center, told Health.

There are four variations, or serotypes, of the dengue virus. If you catch dengue fever, you have lifelong protection from the virus serotype that infected you. “But if somebody has a new infection with a type that they didn’t have before, that’s what’s the highest risk for severe infection,” Bensaci said.

Symptoms of severe dengue include:

• Belly pain or tenderness
• Vomiting at least three times in 24 hours
• Bleeding from the nose or gums
• Vomiting blood or blood in the stool
• Feeling extremely tired or restless

Schein explained that dengue is a hemorrhagic fever, which means it interferes with the blood’s ability to clot and can cause “bleeding, oozing, bruising, and shock.” These severe symptoms can sometimes result in death, she said.

Dengue is typically diagnosed based on a combination of symptoms, recent travel destinations, and lab testing, experts said. For instance, if a patient presents symptoms of dengue fever and has recently traveled to a dengue hotspot, a physician may order a blood test to confirm the diagnosis.

Schein said one symptom in particular—severe bone and joint pain—is a telltale sign that the illness is dengue fever, which is why the disease is nicknamed “breakbone fever.”

There is no specific antiviral medication for dengue, so treatment typically involves managing the symptoms of the disease. If you think you have dengue fever, the CDC recommends:

• Resting as much as possible
• Taking acetaminophen to manage fever and pain (NSAID drugs like aspirin and ibuprofen are not recommended for dengue because they can increase the risk of bleeding complications.)
• Drinking plenty of fluids to stay hydrated

Watch for the signs of severe dengue listed above—which typically begin 24 to 48 hours after your fever goes away—and seek medical support immediately if you experience these symptoms.

Experts said the best way to prevent dengue fever is to avoid mosquitoes. If you’re traveling to or live in an area with high dengue rates, the CDC recommends preventing mosquito bites with the following items:

• Insect repellent registered with the Environmental Protection Agency
• Loose-fitting pants and long-sleeved shirts
• Clothing and gear treated with permethrin, an insecticide that kills or repels mosquitoes
• Mosquito nets, if you’re sleeping outside

The CDC also urges travelers to take these precautions three weeks after they return from their trip. If someone has an infection—whether or not they know it or have symptoms—and gets bitten by a local mosquito, the mosquito can then potentially transmit dengue to other people, Bensaci explained.

Bensaci also recommended taking precautions before you travel, such as checking CDC data for dengue rates in your destination and visiting your primary care physician to assess your risk of severe illness if you do happen to catch dengue.

There is a dengue vaccine, but it is not for the general public. The vaccine is only recommended for children aged 9 to 16 with laboratory confirmation of a previous infection who live in an area where dengue is common.

Despite the risks, experts said the purpose of the CDC health alert was not to deter travel but to inform the public about how to protect themselves.

“We want to make sure we can enjoy having vacation, summer break, and spring break, but in a mindful way,” Bensaci said. “We should all enjoy and travel and explore, but learning and knowledge is the best tool for prevention.”