Dengue Fever: Symptoms, Warning Signs, Testing and Prevention

Introduction: Why dengue fever matters now

Dengue fever is currently the fastest-growing mosquito-borne viral infection worldwide. In 2024, the World Health Organization reported more than 14 million dengue cases and over 10,000 deaths in more than 100 countries. Asia and Latin America carry the highest burden, but the risk for travellers from Europe and other non-endemic regions is increasing as well.

The Asian tiger mosquito (Aedes albopictus) is spreading northwards in Europe due to climate change. For English-speaking patients in Europe, dengue is therefore relevant both as a travel-associated infection and, in the future, potentially as a locally transmitted disease. Understanding symptoms, warning signs, diagnostic testing and prevention is essential to avoid complications.

What is dengue fever?

Dengue fever is a viral infection caused by the dengue virus (DENV). There are four serotypes (DENV-1 to DENV-4). The virus is transmitted to humans through the bite of infected Aedes mosquitoes, mainly Aedes aegypti and Aedes albopictus. Direct person-to-person transmission usually does not occur; the mosquito acts as the vector.

The incubation period is usually 5–7 days (range 3–10 days). Many infections are asymptomatic. When symptoms occur, they typically last 2–7 days. Around one in five people with symptomatic infection develops more intense symptoms, and about one in 20 symptomatic patients will progress to severe dengue, which can be life-threatening without prompt treatment.

Symptoms of dengue fever

Typical symptoms (non-severe dengue)

Typical symptoms of dengue fever include:

• High fever (often 39–40 °C), usually of sudden onset
• Severe headache and pain behind the eyes
• Marked muscle and joint pain (often called "breakbone fever")
• Skin rash (often appearing 2–5 days after fever onset, maculopapular)
• Nausea, vomiting and loss of appetite
• Mild bleeding, such as nosebleeds, gum bleeding or tiny skin spots (petechiae)

Fever may follow a biphasic pattern: after a few days the temperature drops, then sometimes rises slightly again. Many patients feel profoundly exhausted, similar to a very bad flu but often with much more intense muscle and joint pain.

Disease phases

• Febrile phase (days 1–3): high fever, headache, muscle and joint pain, nausea
• Critical phase (days 4–6): fever subsides, warning signs of severe dengue may appear
• Recovery phase (days 7–10): gradual improvement, but fatigue may last for weeks

Warning signs of severe dengue

The most critical period is 24–48 hours AFTER the fever drops. During this phase, fluid can leak from the blood vessels into surrounding tissues, leading to shock and internal bleeding – this is called severe dengue or dengue shock syndrome. The following warning signs require immediate medical attention (emergency care):

• Severe, persistent abdominal pain or abdominal tenderness
• Persistent vomiting (three or more times in 24 hours)
• Bleeding from mucous membranes (nose, gums, blood in vomit or stool)
• Sudden, marked tiredness, confusion or unusual restlessness
• Shortness of breath, rapid shallow breathing, cold hands and feet
• Severe weakness, dizziness when standing, feeling faint

People with underlying conditions (such as heart or kidney disease), pregnant women, young children, older adults and those who have had dengue before are at higher risk of developing severe dengue.

When to seek medical care

As a rule of thumb: anyone who develops fever within 14 days after travelling to a tropical or subtropical region should seek medical advice – ideally from a general practitioner with travel medicine experience or a specialist travel/tropical medicine clinic. For more information, see our guide on Fever After Travel.

Seek medical care or emergency services immediately if:

• Fever above 38.5 °C lasts longer than 2–3 days
• You have severe headache, muscle and joint pain after visiting a dengue-endemic area
• Any of the warning signs listed above appear

Important: Do NOT take painkillers such as ibuprofen, aspirin (acetylsalicylic acid) or other NSAIDs if dengue is suspected, as they increase the risk of bleeding. Paracetamol is usually recommended for fever reduction – always in consultation with healthcare professionals.

Diagnostic testing: NS1, PCR, IgM & more

The choice of dengue test depends mainly on how long symptoms have been present. Modern laboratory methods allow early and relatively accurate diagnosis, particularly when tests are combined.

Recommended tests by illness phase

The NS1 antigen test detects a viral protein and is highly sensitive in the early days of illness. RT-PCR is considered the gold standard in the early phase, as it detects viral RNA directly and can determine the serotype. IgM antibodies usually appear from day 4–5, peak around day 14 and can remain detectable for up to three months.

Combining tests (for example NS1 + IgM or PCR + IgM) significantly increases diagnostic accuracy. A negative test result very early or late in the course of illness does not completely rule out dengue. Test results must always be interpreted together with symptoms, travel history and clinical findings.

Prevention: how to reduce your risk

Because there is no specific antiviral treatment for dengue, prevention is the most important protection. It includes personal mosquito protection, control of breeding sites and – for selected individuals – vaccination.

Personal mosquito protection

• Use insect repellents (for example containing 20–50% DEET, picaridin, IR3535 or oil of lemon eucalyptus) on exposed skin.
• Wear long-sleeved shirts, long trousers and socks, preferably in light colours.
• Stay in air-conditioned rooms where possible and use screens on windows and doors; use mosquito nets.
• Pay special attention to mosquito protection during daytime and in the early morning and evening, when Aedes mosquitoes are most active.
• Discuss repellent use in children, pregnant women and people with skin conditions with a healthcare professional.

Environmental and vector control

Aedes mosquitoes breed in standing water, often in small containers in and around homes. Regular checks help reduce mosquito numbers:

• At least once a week, empty or cover flower pot trays, buckets, rain barrels and other water containers.
• Keep gutters, drains and water outlets clean to prevent water from accumulating.
• Dispose of old tyres, cans, plastic waste and other items that can collect water.
• In endemic areas, support local mosquito control campaigns (for example community clean-up days).

Vaccination against dengue (Qdenga)

In the European Union, the live attenuated vaccine Qdenga (TAK-003) is authorised for people from 4 years of age. In several European countries, expert groups recommend dengue vaccination for selected travellers to high-risk areas, depending on individual risk and destination. Primary immunisation consists of two doses given at least three months apart.

Vaccination does not replace mosquito protection. However, depending on individual circumstances, it can reduce the risk of symptomatic and severe dengue. Whether Qdenga is appropriate for you should be discussed in a travel medicine consultation.

Traveller checklist

Before travel

• Schedule a travel medicine consultation 6–8 weeks before departure.
• Review your vaccination status, including potential dengue vaccination depending on destination.
• Purchase effective mosquito protection (repellents, mosquito nets).
• Check up-to-date dengue information for your destination (for example WHO, CDC, ECDC).

During travel

• Use mosquito protection consistently – during the day and at dusk.
• Avoid standing water in and around your accommodation.
• Seek medical help early if you develop fever or severe pain.

After travel

• If you develop fever within 14 days after returning, always consider dengue and inform your doctor about your trip.
• If warning signs occur (abdominal pain, bleeding, severe weakness), go to an emergency department immediately.

Frequently asked questions (FAQ)

Is dengue contagious from person to person?

Dengue is usually not spread directly from person to person. Transmission almost always requires a mosquito bite. Very rarely, dengue may be transmitted via blood products, organ transplantation or from mother to child around the time of birth.

Can you get dengue more than once?

Yes. Because there are four different serotypes, one dengue infection provides long-term protection only against that serotype. A second infection with a different serotype can increase the risk of severe disease. Therefore, prevention and mosquito protection remain important even if you have had dengue before.

Is there a specific treatment?

There is currently no specific antiviral treatment for dengue virus. Management focuses on adequate fluid intake, careful monitoring and treating complications. Severe cases require hospital care and sometimes intensive care.

References

• World Health Organization (WHO). Dengue and severe dengue – Fact sheet, updated 2024/2025.
• World Health Organization (WHO). Global dengue situation 2024.
• Centers for Disease Control and Prevention (CDC). Dengue – Signs and Symptoms; Clinical Testing Guidance.
• European Centre for Disease Prevention and Control (ECDC). Dengue worldwide overview; Travel-associated dengue cases in the EU/EEA.
• EMA / national expert groups: Qdenga (TAK-003) – Authorisation and recommendations for travellers.