Dengue Fever

What dengue fever is

Dengue is the most common mosquito-borne viral illness in the world. The WHO estimates hundreds of millions of infections every year, and cases have risen sharply over the past two decades as cities have grown and the climate has warmed. It is common across Southeast Asia, South Asia, Latin America and the Caribbean, and local outbreaks occur in Puerto Rico, Florida, Texas and southern Europe.

There are four related dengue viruses. Infection with one type gives lifelong immunity to that type but only brief protection against the others. A second infection with a different type carries a higher risk of severe dengue, because antibodies left over from the first infection can help the new virus enter cells.

How dengue spreads

• Mosquito bites: the main route. Aedes mosquitoes bite mostly during the day, especially in the early morning and late afternoon, and breed in small pools of standing water around homes, such as flower pots, tires and buckets.
• Pregnancy: a mother can pass the virus to her baby around the time of birth.
• Rarely, through blood transfusion or organ transplant.

Dengue does not spread directly from person to person through coughing or touching.

Dengue symptoms

About 3 in 4 infections cause no symptoms at all. When symptoms appear, they start suddenly, 4 to 10 days after the bite. The illness runs in three phases.

1. Febrile phase (days 1 to 3, up to 7)

• sudden fever of 40 °C (104 °F), sometimes in two waves
• severe headache and pain behind the eyes that is worse when moving them
• intense muscle pain, bone and joint pain, which earned it the name "breakbone fever"
• nausea, vomiting and loss of appetite
• a flushed face and a blotchy red skin rash; a later rash may show small white "islands" in a sea of red, and can itch
• mild bleeding, such as tiny red spots on the skin (petechiae), bleeding gums or a nosebleed

2. Critical phase (around days 3 to 7)

As the fever falls, most people start to recover. A minority enter a critical phase lasting 24 to 48 hours, in which small blood vessels become leaky. Fluid moves out of the bloodstream into the belly and chest, and the platelet count drops. This can lead to shock. The fall in temperature can be falsely reassuring, which is why the next few days need close watching.

3. Recovery phase

Fluid moves back into the blood vessels over 2 to 3 days. Appetite returns, and the platelet count rises. A slow heart rate and an itchy rash on the hands and feet are common. Fatigue and low mood can last for weeks.

Warning signs of severe dengue

The WHO and CDC list these signs, usually appearing as the fever settles. Anyone with even one needs hospital assessment the same day:

• belly pain or tenderness
• persistent vomiting (3 or more times in 24 hours)
• fluid buildup in the belly or around the lungs
• bleeding from the gums, nose or other mucous membranes
• lethargy or restlessness
• an enlarged, tender liver
• a rising hematocrit (concentration of red cells in the blood) with a rapidly falling platelet count

Severe dengue, formerly called dengue hemorrhagic fever or dengue shock syndrome, means plasma leakage causing shock or breathing trouble, severe bleeding, or organ damage to the liver, heart or brain.

Who is at higher risk

• people having a second dengue infection
• babies, pregnant people and older adults
• people with diabetes, obesity, kidney disease, heart disease or sickle cell disease

How dengue is diagnosed

A doctor will ask about travel in the previous 2 weeks and check blood pressure, pulse and hydration. A tourniquet test, in which a blood pressure cuff is inflated on the arm for 5 minutes, may show new tiny red spots.

Doctors also consider other fevers that look similar, especially malaria, which can be deadly and needs its own test, plus chikungunya, Zika, leptospirosis, typhoid fever, flu and COVID-19.

Dengue treatment

There is no antiviral medicine for dengue. Treatment supports the body until the virus clears.

Mild dengue at home

• Fluids: drink water, oral rehydration solution, soups and juices often. Aim for pale urine every few hours.
• Fever and pain: acetaminophen (paracetamol) only, at the label dose, without exceeding the daily maximum.
• Avoid aspirin, ibuprofen, naproxen and other NSAIDs. They increase the risk of bleeding.
• Rest, and have someone check on you for warning signs, especially as the fever falls.
• Prevent spread: stay under a bed net or in a screened room for the first week, so local mosquitoes do not pick up the virus from you.

Many clinics arrange a daily blood count and check-up until 48 hours after the fever ends.

Hospital care

People with warning signs or severe dengue receive carefully measured intravenous fluids, with frequent blood tests to guide how much to give. Too little allows shock, and too much causes fluid overload once the leak reverses. Blood transfusion is used for significant bleeding. Platelet transfusions are not given simply for a low count, because they do not prevent bleeding in dengue. With good hospital care, deaths from severe dengue are below 1%.

Prevention

Avoid bites

• Use an EPA-registered insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus. Apply sunscreen first, then repellent.
• Wear long sleeves and long pants, treated with permethrin if possible.
• Stay in places with window screens or air conditioning.
• Empty and scrub containers that hold water at least weekly.

Dengue vaccines

• Qdenga (TAK-003) is licensed in the UK, the European Union and several dengue-endemic countries for people aged 4 and over. It is not available in the US.
• Dengvaxia was approved in the US only for children aged 9 to 16 with laboratory-confirmed past dengue who live in endemic US territories, because it increases the risk of severe disease in people never infected before. Its manufacturer is phasing it out.

Ask a travel clinic which options apply to your destination and history.

Frequently asked questions

What are the first symptoms of dengue fever?

Dengue usually starts suddenly with a high fever around 40 °C (104 °F), severe headache, pain behind the eyes, and muscle and joint aches, 4 to 10 days after a mosquito bite. Nausea, vomiting and a red rash often follow. Some people have mild bleeding from the gums or nose.

What are the warning signs of severe dengue?

Severe belly pain, repeated vomiting, bleeding from the gums or nose, vomiting blood, black stools, drowsiness or restlessness, and cold clammy skin. They usually appear as the fever goes down, between days 3 and 7. Anyone with these signs needs emergency hospital care.

Can you get dengue twice?

Yes. There are four dengue virus types, and recovering from one only protects you against that type. A second infection with a different type is more likely to become severe, so people who have had dengue before should be especially careful about mosquito bites and warning signs.

Why can't I take ibuprofen for dengue?

Ibuprofen, aspirin and other NSAIDs reduce platelet function and can irritate the stomach lining. Dengue already lowers platelets and can cause bleeding, so these medicines increase the risk of serious hemorrhage. Use acetaminophen (paracetamol) at the label dose instead.

How long does dengue fever last?

The fever typically lasts 2 to 7 days. Most people feel much better within about a week, though tiredness, low mood and poor appetite can last several weeks. The most dangerous period is the 24 to 48 hours after the fever falls.

Is dengue contagious from person to person?

No. Dengue does not spread through coughing, kissing or touching. It spreads through mosquito bites, and occasionally from mother to baby around birth or through transfusion. A sick person can infect local mosquitoes, which is why bed nets help during the first week.