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Dengue is spread via mosquitoes. Leslie F. Miller/Getty Images
  • Puerto Rico’s health department has declared an emergency due to dengue.
  • Cases of dengue and other mosquito-borne diseases are surging this year across the Americas, the Caribbean, and Brazil in particular.
  • While dengue is not serious for many people, the more severe form of the disease can result in hospitalization and death.

Cases of dengue, a mosquito-borne disease, are surging in Puerto Rico, prompting the island’s health department to declare a public health emergency.

There have been 549 reported cases of the disease this year, according to Puerto Rico’s health department. Meanwhile in 2023, the total number of cases was 1,293 for the entire year.

“This year, dengue cases have surpassed historical figures,” said Puerto Rico Secretary of Health, Carlos Mellado López, in a statement.

Dengue has regularly been documented in the continental United States, particularly in southern Florida. In 2023, there were 642 cases of dengue in the United States, according to the CDC.

About half of the world’s population is at risk of dengue, with between 100-400 million infections occurring annually, according to the World Health Organization. The majority of cases so far this year have appeared in the Americas and Caribbean. Brazil has become the epicenter for dengue, with more than 60% of global cases occurring there — about 2.9 million.

Other mosquito-borne diseases, including zika, chikungunya, yellow fever, have also been on the rise globally.

Peter J. Hotez, MD, PhD, Co-director of the Texas Children’s Hospital Center for Vaccine Development and dean of the National School of Tropical Medicine at Baylor College of Medicine, told Healthline that the causes for the increase in these diseases are complex and multifactorial.

“It’s happening because of a confluence of a number of forces, which include global warming, climate change, and urbanization together with poverty. Those three things seem to be creating a toxic mix,” he said.

Those factors have created an environment in which mosquitoes are thriving in close proximity to densely populated areas.

One mosquito in particular is responsible for transmitting dengue, chikungunya, yellow fever, and zika: the aedes aegypti or aedes mosquito.

“They’re really voracious feeders. The females are feeding all the time and they’re often biting multiple people,” Bob Bollinger, MD, MPH, a Professor of Infectious Diseases at Johns Hopkins University School of Medicine, told Healthline.

Dengue, which is caused by the dengue virus, is transmitted through blood, making mosquitoes the perfect vector.

“If they happen to bite somebody that has dengue virus in their blood, they’ll take that virus up in their blood meal, and then the next time they bite somebody they basically transmit it to that person as well,” said Bollinger.

Unlike viruses that originate in other animals which can then be spread to humans, dengue is spread directly from humans to mosquitoes and then to other humans. Although uncommon, dengue can also be passed down maternally from an infected mother, and through blood transfusions.

In areas where dengue is present, it is continually being transmitted, although it may be unnoticed and not rise to epidemic proportions.

“Dengue virus is kind of always percolating along at a low level right now in different parts of the world,” Dawn Wesson, PhD, an Associate Professor at Tulane University School of Public Health and Tropical Medicine, told Healthline.

“Even during the dry season or in times when there’s not a lot of transmission going on, there’s some low level transmission. So it’s never stopping in some of these tropical parts of the world. It’s just kind of constantly going and at certain times it erupts,” she said.

There are two forms of the disease caused by the dengue virus: dengue and severe dengue. One-in-four people infected will get sick, while only one-in-20 will experience symptoms of severe dengue, according to the CDC.

In its mildest form, it may even go unnoticed, though it is still transmissible.

“A lot of people can have it. They can feel just fine and get on a plane and go someplace else. So, it wouldn’t surprise me as a result of this if we start seeing cases in southern Florida,” said Wesson.

Signs and symptoms of dengue can include:

  • Fever (the most common symptom)
  • Nausea
  • Vomiting
  • Aches and pains
  • Rash
  • Pain behind the eyes

Dengue usually lasts 2-7 days and individuals will typically recover on their own after about one week.

Some people will develop severe dengue. Those who have previously been infected with dengue are more likely to develop the more serious condition.

Severe dengue can be fatal and may require hospitalization.

Symptoms of severe dengue include:

  • Persistent vomiting
  • Bleeding gums or nose
  • Severe abdominal pain
  • Rapid breathing
  • Blood in vomit or stool
  • Weakness

Severe dengue is also more likely to affect vulnerable populations.

“Severe dengue is more common in people with underlying conditions, very much like covid, meaning diabetes and hypertension. So those are the ones often that wind up having to go to the ICU,” said Hotez.

There is no treatment for dengue, that is, there is no antiviral medication formulated specifically for the disease. While there is a vaccine for the disease, it is not widely available, nor is it approved in all areas of the world. Dengue is treated with supportive care and pain medication, such as acetaminophen, and severe dengue can require hospitalization.

In the United States, there is an approved dengue vaccine for children between the ages of 9-16, and only if they have already had a laboratory-confirmed case of dengue. It is only administered in areas where dengue is endemic, and occurs regularly.

A dengue vaccine has proven difficult to create due to the genetic makeup of the dengue virus. There are four serotypes (varieties) of dengue virus, which share much of their genetic material but are all slightly different. Someone who has been infected with one serotype will become immune to just that one variety, although they will also have some limited immunity to the others for a few months.

After the immunity has worn off, that person can then be infected by the other serotypes, and puts them at a greater risk of severe dengue.

Due to the lack of treatment and effective vaccines, the top priority in dengue (and other mosquito-borne illness) prevention is through controlling mosquito populations.

“If you control the mosquito, you’re going to reduce transmission. However, this mosquito is a very difficult mosquito to deal with,” said William Schaffner, MD, a Professor of Infectious Diseases and Preventative Medicine at Vanderbilt University.

Mosquitoes require water to breed, so making sure to clean up areas of standing water, even small amounts of it, around the home will help control mosquito populations.

The other major component of prevention, said Schaffner, is personal protection. That means common sense things like wearing long clothing, using insect repellant, and installing screens or other protective measures around the home.

“Do whatever you can to protect yourself if you’re not vaccinated, and most people aren’t. So keep that repellent on hand and use it when you are out and the mosquitoes are out,” said Wesson.

The Puerto Rico health department has declared an emergency due to surging cases of dengue. Dengue is a mosquito-borne disease that causes fever, aches, and nausea.

A more serious form of dengue, called severe dengue, can cause internal bleeding, hospitalization, and death.

There is currently no treatment for dengue, but most people recover in about a week. While there is a vaccine, it is only available to children who have already had a confirmed case of dengue.