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Dengue fever spreads fast. How can you protect yourself as cases explode in Puerto Rico and other popular travel destinations?

Mosquitos in a petri dish.
Puerto Rico just declared a public health emergency due to an epidemic of dengue fever, transmitted by mosquitos. Cases are exploding in the Americas. Photo by Luis ROBAYO via Getty Images

Cases of dengue fever, a potentially deadly mosquito-borne illness, have skyrocketed in Puerto Rico, prompting officials there to warn that the problem has reached epidemic levels. 

The outbreak in the U.S. territory has sickened at least 549 people on the island and hospitalized 340 since the start of 2024, a 140% increase in cases over the same time last year, according to the island’s Department of Health.  

But the public health emergency extends far beyond Puerto Rico. The Centers for Disease Control and Prevention has announced first-level travel alerts regarding dengue fever in nearly 20 dozen Central and South American countries including Costa Rica and Jamaica. 

Northeastern health experts Richard Wamai and Neil Maniar say the key to preventing dengue fever is avoiding mosquito bites. When people are infected, early detection can help prevent severe illness and death.

“With climate change, we have an increase in the hot, humid climate that is conducive to an explosion in the population of mosquitoes that increases the risk of mosquito-borne” illness, says Maniar, director of the Master of Public Health program at Northeastern.

Cases of the mosquito-borne disease already have risen by 249% in the Western Hemisphere this year compared to the same time period in 2023, according to the European Centre for Disease Prevention and Control, a situation the World Health Organization describes as unprecedented.

Brazil already has experienced 1.5 million cases of dengue in 2024, with 278 deaths, says Wamai, Northeastern professor of Cultures, Societies and Global Studies and an expert in neglected tropical diseases.

“Really, prevention is the most important thing people can do, avoiding the bite of the mosquito,” Wamai says.

What is dengue fever?

Dengue is a viral illness transmitted by the bite of an infected female Aedes mosquito, the same species that spreads Zika, chikungunya and other viruses.

It’s not contagious from person to person, but if an infected person is bitten by a mosquito, the insect can spread the virus to the next person it bites, Wamai says.

“The transmission can occur pretty rapidly when you have a dense susceptible population,” he says.

Symptoms can include fever with nausea, vomiting, rash, headache, eye pain and joint and muscle pain, according to the CDC

Not every infected person develops symptoms, which tend to occur within two weeks of a bite. But in severe cases, “dengue can cause shock, internal bleeding and even death,” according to the CDC, which says up to 40,000 people die annually from dengue.

No cure, but a vaccine for eligible children

There is no cure for dengue fever. Treatment consists of pain relief and symptom management with medications such as acetaminophen. The CDC says ibuprofen and aspirin are to be avoided because they can increase the risk of bleeding.

The people most at risk of a severe case of dengue are those who are reinfected after experiencing an infection in the past, Maniar says.

The CDC says a dengue vaccine is now available for children and teens ages 9 to 16 who were previously infected, as confirmed by lab tests, and who live in locations including Puerto Rico, American Samoa and the U.S. Virgin Islands. 

“If you haven’t been infected with dengue, the CDC does not recommend the vaccine,” Wamai says.

The role of warmer winters

Milder winters are extending the season for Aedes mosquitoes because they like it warm but not too hot, Wamai says.

“You have climates that are becoming more favorable” to mosquito-borne illness, Maniar says.

About half the world’s population is at risk from dengue fever, according to Dr. Raman Velayudhan of the World Health Organization.

Since the start of 2023, dengue cases have spiked to a historic high of more than 5 million cases and more than 5,000 dengue-related deaths, with close to 80% of infections occurring in the Western Hemisphere, WHO officials say, adding that “explosive outbreaks are occurring.”

Is dengue a problem on the U.S. mainland?

So far dengue fever has not reached the levels of a public emergency in the continental United States, where it has been seen in Florida, Hawaii, Texas, Arizona and California.

As of February, there were two locally acquired cases of dengue in Florida, but most of the hundreds of cases reported on the U.S. mainland every year involve individuals who picked up the disease on their travels outside of the states.

The number one tool currently available to fight dengue is “prevention, prevention, prevention,” Wamai says.