Dengue (pronounced DENgee) fever is a painful, debilitating mosquito-borne disease caused by any one of four closely related dengue viruses. These viruses are related to the viruses that cause West Nile infection and yellow fever.

An estimated 400 million dengue infections occur worldwide each year, with about 96 million resulting in illness. Most cases occur in tropical areas of the world, with the greatest risk occurring in:

• The Indian subcontinent
• Southeast Asia
• Southern China
• Taiwan
• The Pacific Islands
• The Caribbean (except Cuba and the Cayman Islands)
• Mexico
• Africa
• Central and South America (except Chile, Paraguay, and Argentina)

Most cases in the United States occur in people who contracted the infection while traveling abroad. But the risk is increasing for people living along the Texas-Mexico border and in other parts of the southern United States. In 2014, an outbreak of dengue fever was identified in Hawaii with other outbreaks in 2013 in Brownsville, Texas and Key West, Fla.

Symptoms

Many people experience no signs or symptoms of a dengue infection.

When symptoms do occur, they may be mistaken for other illnesses — such as the flu — and usually begin four to 10 days after you are bitten by an infected mosquito.

Dengue fever causes a high fever — 104 F (40 C) — and any of the following signs and symptoms:

• Headache
• Muscle, bone or joint pain
• Nausea
• Vomiting
• Pain behind the eyes
• Swollen glands
• Rash

Most people recover within a week or so. In some cases, symptoms worsen and can become life-threatening. This is called severe dengue, dengue hemorrhagic fever or dengue shock syndrome.

Severe dengue happens when your blood vessels become damaged and leaky. And the number of clot-forming cells (platelets) in your bloodstream drops. This can lead to shock, internal bleeding, organ failure and even death.

Warning signs of severe dengue fever — which is a life-threatening emergency — can develop quickly. The warning signs usually begin the first day or two after your fever goes away, and may include:

• Severe stomach pain
• Persistent vomiting
• Bleeding from your gums or nose
• Blood in your urine, stools or vomit
• Bleeding under the skin, which might look like bruising
• Difficult or rapid breathing
• Fatigue
• Irritability or restlessness

When to see a doctor

Severe dengue fever is a life-threatening medical emergency. Seek immediate medical attention if you’ve recently visited an area in which dengue fever is known to occur, you have had a fever and you develop any of the warning signs. Warning signs include severe stomach pain, vomiting, difficulty breathing, or blood in your nose, gums, vomit or stools.

If you’ve been traveling recently and develop a fever and mild symptoms of dengue fever, call your doctor.