For centuries, there were legends of evil spirits lurking in the tropics that would cause severe illness to visitors. Travelers would experience fever, chills, headaches, extreme fatigue and painful body aches.

Today, we know these are, in fact, the symptoms of dengue, caused not by looming malevolent spirits but rather by mosquito bites. Dengue is a mosquito-borne viral infection that causes fever, generalized body aches, and, if severe, external and internal bleeding (called dengue hemorrhagic fever).

For individuals living or traveling where dengue is common, there are important things to know to recognize potential signs of the disease and minimize the risk of infection. Here’s a closer look at what people should know about dengue.

1. Not all mosquitoes carry dengue

Usually, dengue is spread to people through the bites of infected Aedes species mosquitoes. Each year, about 50 to 100 million cases of dengue and about 20,000 deaths occur worldwide. However, in the United States, only about 100 to 200 cases occur yearly, nearly all brought in by travelers returning from affected areas.

2. Dengue is spreading to new areas

Dengue is common in the tropics and subtropics worldwide. It is most common in Southeast Asia but has become more common in Central and South America, with record numbers of cases in countries including Brazil. Most often, cases of dengue reported in the United States occur in people who recently traveled to parts of the world where dengue is common.

At the same time, Aedes mosquitoes are turning up in new places due to human activity and a changing climate. In the United States, they’ve been found in states including Florida, Southern California, Texas, Arizona and the Midwest. A few cases of locally transmitted dengue have occurred in Hawaii, Florida and Texas.

3. Dengue comes in three phases

Dengue varies in severity, and not everyone who gets infected gets seriously ill. But for those who do, it can be very serious. Dengue symptoms typically begin suddenly, causing fever, chills, a severe headache, pain when the eyes are moved, extreme fatigue and severe generalized body aches, particularly in the back, legs, and joints. These aches are often so painful that the disease has been called “breakbone fever.”

These symptoms typically last for a few days, after which patients begin to feel better for about 24 hours. People may think they’re out of the woods, but then the fever can return, along with more serious effects, including dengue hemorrhagic fever, bleeding and shock.

4. Dengue is not contagious

In a vast majority of instances, people with dengue cannot transmit it to others. A mosquito can transmit it by biting a person with an infection and then biting someone else. Although uncommon, a pregnant woman can pass the dengue virus to her fetus during pregnancy or around the time of birth. There has been one report of dengue virus passing through breast milk.

5. There is currently no vaccine against new cases

The only dengue vaccine currently available in the United States is approved for children who have been previously infected and live in an area where the disease is common. There are a number of vaccines in development that can be used for individuals who have not had prior dengue infections as well as those who have.

6. Travelers need to take precautions

Anyone traveling to parts of the world where dengue is common should take steps to protect themselves and their fellow travelers. Before the trip, visit a travel medicine clinic and talk to the doctor about potential risks and precautions. Current recommendations and advisories are available via public health agencies like the Centers for Disease Control and Prevention. Keep in mind data often may be up to a week behind actual levels.

When traveling, the same best practices around avoiding all mosquito bites apply. Wear light-colored, long-sleeved, loose-fitting clothing. Use insect repellant. Repellants are increasingly being added to sunscreens. Just be sure to check the labels before using any product on children.

Ultimately, the best way to reduce the risk of dengue is to reduce the number of mosquitoes that carry it. It can be challenging to eliminate all breeding sites, but there are also innovative steps being taken to reduce mosquito populations, including introducing genetically modified mosquitoes into populations and through bacteria that blocks mosquitoes from being infected with dengue.

7. Travelers should watch for symptoms

Symptoms of dengue typically begin about 3 to 15 days after being bitten by an infected mosquito. Often, a traveler only starts to feel sick after they return home. If you’ve traveled and start to feel sick, it’s essential that you provide travel details when talking to your doctor.

For more on dengue, visit The Manuals page or the Quick Facts on the topic.