Dengue Cases Are on the Rise

The mosquito-borne illness is a growing threat to Americans, CDC warns

Rachel Nania,

AARP

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En español

Published June 26, 2024

mosquito biting an arm with a pink background

Photo Collage: AARP (Source: Shutterstock)

Health officials issued an alert June 25 to warn health care providers and the public of an increased risk of dengue virus infections in the U.S.

Globally, cases of the mosquito-borne disease have been the highest on record this year, the advisory from the Centers for Disease Control and Prevention (CDC) said. And countries in the Americas have reported twice as many dengue cases so far this calendar year — nearly 10 million — as in all of 2023, with many of the outbreaks occurring in Central and South America.

In the U.S., a “higher than expected” number of dengue cases have been reported. There have been a 2,241 in 2024, including 1,498 in Puerto Rico, which declared a public health emergency in March due to the concerning number of cases that came during a time of year when counts are usually lower.

Cases in the Americas have “skyrocketed this year,” Robert Murphy, M.D., an infectious disease expert and executive director of the Robert J. Havey, MD Institute for Global Health at Northwestern University Feinberg School of Medicine, told AARP in December. And the CDC says cases will likely keep climbing as global temperatures increase. The 10 warmest years on record have all occurred in the past decade, data from the National Oceanic and Atmospheric Administration shows. Higher temperatures expand the range of the mosquitoes that transmit dengue.

In addition to changing weather patterns, the swell in cases could also be due to more testing, says Michael Friedman, M.D., a global public health expert and former CDC chief medical officer, epidemiologist and country director.

“But regardless of that, this increase is a concern for sure,” he says.

What is dengue?

Dengue is a disease that’s caused by four related viruses commonly found in tropical regions that can be transmitted to humans by an infected mosquito from the Aedes species, according to the National Foundation for Infectious Diseases. This type of mosquito also carries the Zika and chikungunya viruses.

A dengue infection doesn’t always cause a person to get sick, but those who do get sick typically experience symptoms that are similar to many other viral infections. The most common symptom is a fever (the illness is sometimes called dengue fever) that can be paired with:

Aches and pains behind the eyes
Muscle, joint or bone pain
Nausea or vomiting
Rash

For some people, the illness is mild and clears in about a week. For others, a dengue infection can become severe — even life-threatening — and older adults are among the populations at higher risk for a serious case. A previous dengue infection can also increase risk for a severe case.

About 5 percent of people who have symptoms from a dengue infection will go on to develop severe disease, the Cleveland Clinic says. Warning signs of a severe dengue infection include:

Abdominal pain
Frequent vomiting
Nose bleeds or bleeding gums
Extreme tiredness, restlessness or irritability
Throwing up blood or blood in your poop

What’s tricky is these scary symptoms pop up after initial symptoms start to fade — they’re usually seen 24 to 48 hours after the fever goes away.

Will dengue affect summer travel?

Summer travel for many Americans overlaps with the months of increased dengue activity in other countries, the CDC notes. The latest alert is no reason to cancel a trip you have planned, Friedman says, but “it's one more thing [travelers] have to be concerned about.”

There are some things you can do to lower your risk of a dengue infection if you’re planning a trip to an area with high or frequent transmission, which includes the Caribbean, Central America, South America, Southeast Asia and the Pacific Islands.

Use an Environmental Protection Agency-approved mosquito repellent.
Wear loose-fitting, long-sleeved shirts and pants.
Wear clothing and gear treated with the insecticide permethrin.
Use air conditioning or window screens when possible to keep mosquitoes out from any indoor areas.

Also, pay attention to the time of day you’re most active outside.

“The biggest risk time for these mosquitoes biting is around dusk — late afternoon, early evening,” Friedman says. “And so during that time period, try to wear something that's long sleeve, try to cover your ankles and use insect repellent.”

Currently, there is no vaccine for U.S. travelers who are visiting an area where dengue is common. (There was an approved vaccine in the U.S. for children ages 9 to 16 who had dengue previously, but the manufacturer has stopped making it. Puerto Rico will continue to have access to the vaccine until available doses expire in 2026.)

With scientists actively pursuing other options, more vaccines could become available in the coming years.

“My prediction is that at some point in the near future we will have more dengue vaccines available for the public,” Friedman says.

Which states experience dengue outbreaks?

Most of the reported cases in the U.S. are in travelers who were infected elsewhere.

That said, dengue transmission does occur in the U.S., since the types of mosquitoes that spread it are common throughout many areas. However, so-called local spread is usually limited, the CDC says, “with sporadic cases or small outbreaks in Florida, Hawaii, and Texas.” California and Arizona have also seen local cases.

That could change in the future, Friedman says: “My hunch is that it’s going to increase.”

To reduce your risk at home, you can do the same things that are recommended for travelers — wear insect repellent and long-sleeved shirts and pants when possible.

Also be sure to dump and drain containers with standing water to reduce mosquito egg-laying sites around your home — this can include bird baths, flowerpots and clogged gutters. And repair any holes you have in window and door screens to keep mosquitoes outside.

If you come down with dengue symptoms and live in or traveled to an area where it’s common, let your doctor know. The CDC alert urges health care professionals to “maintain a high suspicion” in patients who may have come into contact with the virus; a simple blood test can detect it and confirm an infection.

There is no specific treatment for dengue — rest and over-the-counter fever reducers are often recommended. What’s important is to keep an eye on any worsening symptoms. Dengue can become severe within a few hours, the CDC says, and severe dengue is a medical emergency.

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