Dengue fever, also known as dengue, is an illness caused by infection with any of four closely related dengue viruses. It is transmitted to humans via the bites of infected mosquitoes. Most people who become infected do not develop symptoms or instead have mild symptoms, such as fever, headache, pain behind the eyes, nausea, vomiting, and/or rash. Dengue is sometimes called “breakbone fever” because, in addition to fever, it can cause severe aches and pains, especially in the legs, joints, and back (dengue does not actually cause bones to break). Around 1 out of every 20 people infected by a dengue virus develops severe dengue, a life-threatening medical emergency that requires immediate medical attention.

Dengue is most commonly found in tropical and subtropical regions around the world, including some United States territories, such as Puerto Rico, the U.S. Virgin Islands, and American Samoa. Dengue infections have also occurred in the continental U.S., including in Florida, Hawaii, Texas, Arizona, and California.

The World Health Organization (WHO) reports that the occurrence of dengue has grown 30-fold over the previous 50 years. In recent years, cases of dengue have continued to increase worldwide. According to the Centers for Disease Control and Prevention (CDC), in 2023, there were 4.6 million reported cases in the Americas, resulting in 4,000 deaths. By late June 2024, over 9.7 million cases of dengue had been reported in the Americas, more than double the number of reported cases throughout the previous year. The CDC notes that case numbers are likely to continue to rise as temperatures climb around the world. Warmer weather allows the mosquitoes that transmit dengue virus to expand their geographic range.

While there is no cure for dengue and there are no specific medications for the condition, getting adequate hydration and plenty of rest, and taking acetaminophen for pain and fever can help alleviate symptoms while the body’s immune system fights the virus. In most cases, people recover from dengue within a week. For those with severe dengue, treatment by health care professionals can significantly lower the risk of death.

Dengue is caused by an infection by any of four different, but closely related, dengue viruses:

• Dengue virus type 1 (DENV-1 or DEN-1)
• Dengue virus type 2 (DENV-2 or DEN-2)
• Dengue virus type 3 (DENV-3 or DEN-3)
• Dengue virus type 4 (DENV-4 or DEN-4)

The four dengue viruses are spread to humans through the bites of infected female mosquitos, in particular, Aedes aegypti mosquitoes, though other Aedes mosquito species can also transmit the virus to people.

When people are infected by and recover from one of the dengue viruses, they have lifelong immunity against the virus type that caused their infection. However, they can be infected by other types of dengue virus. Additionally, people who have had a previous dengue infection are at increased risk of developing severe dengue if they have a second infection.

Uninfected female Aedes mosquitos can become infected by a dengue virus when they bite an infected person. The virus passes from human to mosquito and replicates inside the mosquito. Once infected, a mosquito can then transmit the virus to humans for the rest of its life. While dengue infections can occur at any time of the year, the number of cases typically increases during the rainy season.

Less commonly, the virus can be transmitted from a pregnant person to the fetus during pregnancy or around the time of birth.

In rare cases, people can become infected by a dengue virus via:

• Blood transfusions
• Organ transplants
• Needlestick injuries

Dengue fever is endemic (meaning it is constantly present within a specific geographic area) in subtropical and tropical regions around the world, including in some United States territories such as Puerto Rico, the U.S. Virgin Islands, and U.S.-affiliated Pacific Islands.

Dengue is endemic in over 100 countries in the following regions:

• Southeast Asia
• Western Pacific
• Americas
• Africa
• Eastern Mediterranean

The Americas, southeast Asia, and the western Pacific are the most severely affected areas.

The CDC maintains a map—known as DengueMap—that displays information about the risk of dengue as well as recent cases of dengue in countries around the world. The health agency also provides data on dengue cases in the U.S. over the past year as well as historic data since 2010.

Most people with dengue have no symptoms or only mild symptoms.

However, if symptoms do occur, they typically include:

• Fever (usually begins four to seven days after getting bitten by an infected mosquito)
• Pain behind the eyes
• Muscle, joint, or bone pain
• Nausea and vomiting
• Swollen lymph nodes
• Rash (two to five days after a fever begins, a flat, red rash may develop; three to six days after a fever begins, a second rash of raised bumps may appear)

Usually, symptoms last for two to seven days.

Around 1 out of every 20 people with dengue develop severe dengue. Severe dengue is a life-threatening condition and a medical emergency. Dengue can develop into severe dengue over the course of only a few hours. Warning signs of severe dengue may occur 24 to 48 hours after the fever goes away. Anyone with any of the following warning signs of progression to severe dengue should seek immediate medical attention:

• Severe stomach pain and tenderness
• Persistent vomiting
• Rapid breathing
• Bleeding gums or nose
• Feeling extremely tired
• Restlessness
• Blood in vomit or stool
• Bleeding under the skin (may appear as purplish dots or patches under the skin)

Symptoms of severe dengue include:

• Shock (a life-threatening condition in which blood pressure is low and the organs and tissues do not receive enough blood and oxygen) or accumulation of fluid in the abdominal cavity (ascites), lungs (pulmonary edema), or space between the lung and chest wall (pleural effusion) with difficulty breathing. Shock and fluid buildup can occur due to the severe leakage of plasma—the liquid portion of the blood—from blood vessels
• Severe bleeding
• Severe organ involvement that can lead to impaired consciousness (lower than normal responsiveness to touch, sound, or other stimuli) and organ failure

To diagnose dengue fever, doctors typically review the patient’s medical history, conduct a physical exam, and order one or more diagnostic tests.

The doctor will ask about symptoms, including when they began and whether they include nausea, vomiting, rash, aches and pain, bleeding under the skin, or any warning signs for severe dengue. The doctor will also ask whether the patient has recently spent time in areas where dengue virus is present.

During the physical exam, the doctor will check for signs and symptoms of dengue, including fever, rash, bleeding under the skin, swollen lymph nodes, and warning signs of severe dengue.

Diagnostic blood tests can confirm the diagnosis. They work by detecting components of the virus or antibodies (produced by the patient’s immune system) against the dengue virus in the blood sample. Different types of tests are available, and the choice of test depends on the time since the onset of symptoms. These tests include:

• Molecular tests (nucleic acid amplification test, NAAT) to detect nucleic acid (specifically ribonucleic acid, RNA) from the dengue virus in the blood sample. (Nucleic acids are biological molecules that perform important roles in cells and viruses.)
• NS1 antigen test to detect a protein from the dengue virus called nonstructural protein 1 (NS1).
• Serologic tests to detect antibodies (made by the patient’s immune system) against the dengue virus.

The doctor may conduct or order additional tests as well, including:

• Tourniquet test, a test used to assess the fragility of blood vessels. In dengue, the blood vessels may become fragile and leak blood. In this test, the health care provider inflates a blood pressure cuff around the upper arm and leaves it in place for five minutes. The provider then removes the cuff and, one to two minutes later, checks for petechiae (small red dots that indicate bleeding under the skin). The test is positive (suggesting the patient may have dengue) if 10 or more new petechiae are present within a one-inch square of skin.
• Blood tests, including a complete blood count (CBC) and kidney and liver function tests, among others, may help in making a diagnosis.
• X-rays of the chest and ultrasound imaging of the chest and abdomen may be done to check for pulmonary edema, pulmonary effusion, and ascites.

There is no cure for dengue, and there are no antivirals or other medications to treat it. Because most cases of dengue resolve on their own within a week or two, treatment is supportive, meaning it aims to reduce symptoms.

People with dengue who do not have any warning signs of severe dengue can usually be cared for at home. At-home treatment includes:

• Rest
• Drink plenty of fluids
• Take acetaminophen (e.g., Tylenol) to manage fever and pain
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, naproxen, and aspirin, should be avoided because they can increase the risk of bleeding.

Immediate medical attention is necessary if any warning signs of severe dengue are present. Infants, pregnant people, older adults, and people with certain conditions, including diabetes, kidney failure, and obesity, who are at greater risk of severe dengue, may need to be treated in a hospital or clinic.

Treatment for people with severe dengue warning signs or severe dengue may include:

• Oral or IV fluids
• Blood transfusion

The best way to prevent dengue is to avoid getting bitten by infected mosquitos.

People can lower the risk of mosquito bites in several ways, including:

• Avoid areas where dengue virus is present
• Use insect repellent. The CDC recommends repellents with any of the following active ingredients:
  • DEET
  • Picaridin (also known as KBR 3023, Bayrepel, and icaridin)
  • Oil of lemon eucalyptus (OLE)
  • Para-menthane-3, 8 diol (PMD)
  • IR3535
• Wear long-sleeved shirts, pants, and socks to minimize skin exposure
• Wear clothing treated with permethrin (an insecticide)
• Stay in places with air conditioning or screened windows and doors
• Sleep under a mosquito net (insecticide-treated nets are available)
• Take steps to control mosquitos in and around homes (e.g., remove standing water, use insecticides)

In 2019, the Food and Drug Administration (FDA) approved Dengvaxia®, a dengue vaccine, for children and adolescents ages 6 through 16 who have had a previous dengue infection and who live in areas where dengue is endemic. The vaccine works against all four dengue viruses and has an efficacy of around 80% against hospitalization and severe dengue.

The vaccine is only for individuals who have had a previous laboratory-confirmed dengue virus infection, meaning a previous infection must be confirmed through a blood test before vaccination. This may be done by consulting previous dengue infection test results in an individual’s medical record or via a pre-vaccination screening test to check for evidence of a previous infection. For individuals who have never had a dengue infection, getting the Dengvaxia vaccine increases the risk of severe dengue if they are later infected with a dengue virus.

Dengvaxia requires three doses given by injection. The doses are administered six months apart. The most common side effects from the vaccine include pain at the injection site, headache, a general feeling of discomfort or illness, weakness, and muscle aches and pain. The side effects typically resolve within a few days.

According to the CDC, Sanofi Pasteur, the vaccine division of the French pharmaceutical company Sanofi, will stop manufacturing the vaccine, citing a lack of demand. The last doses of Dengvaxia will expire in 2026.

There are no other FDA-approved vaccines against dengue.

Most people who are infected by a dengue virus do not develop symptoms or have mild symptoms. In these cases, most people recover within a week.

According to the CDC, only around 25% of people infected by a dengue virus develop symptoms and approximately 5% of people with dengue develop severe dengue, a life-threatening condition that can cause shock and internal bleeding. Without treatment, the mortality rate of severe dengue can range from 10% to 20%. With treatment, however, the rate falls to 1%.

This article was medically reviewed by Joseph Vinetz, MD, a Yale Medicine expert in general infectious diseases with special expertise in tropical medicine and traveler's health.