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Health condition · Clinically reviewed

Dengue fever, phases, warning signs and the Qdenga vaccine.

A mosquito-borne flavivirus with a predictable clinical rhythm - febrile, critical, recovery. In the UK it is travel-related today, but the map is changing.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against WHO, UKHSA, NaTHNaC and specialist tropical medicine sources listed at the end.

  • 03

    Current for 2026

    Reflects modern WHO 2009 classification, Qdenga vaccine availability and expanding European transmission risk.

Key facts

Dengue at a glance.

The essentials, in plain English - what it is, where it is spreading, and how it is managed in the UK today.

  • What it is

    A mosquito-borne flavivirus infection spread by Aedes aegypti and Aedes albopictus, with four serotypes (DENV 1 to 4) and an emerging fifth.

  • Where

    Endemic across the tropics and subtropics, with growing autochthonous outbreaks in Southern Europe (Italy, France, Spain in 2024).

  • UK picture

    Currently travel-imported only, with no sustained local transmission, but Aedes albopictus expansion is being monitored.

  • Classification

    WHO 2009: Dengue (with or without warning signs) and Severe Dengue. Three clinical phases follow a predictable pattern.

  • Second infection

    Infection with a second serotype increases the risk of severe disease through antibody-dependent enhancement (ADE).

  • Treatment

    No specific antiviral. Supportive care with careful fluid balance, paracetamol only, and ICU support for severe disease.

Why this guide matters

A predictable illness with a dangerous middle.

Dengue moves through three defined phases. Recognising the critical phase and its warning signs is what turns a self-limiting illness into a safe one.

  • Three-phase illness

    A febrile phase of 3 to 7 days, a critical phase around defervescence and a recovery phase. Each has its own risks and priorities.

  • Warning signs matter

    Abdominal pain, persistent vomiting, mucosal bleeding, lethargy and a rising haematocrit with falling platelets all trigger hospital admission.

  • Second infection risk

    A different serotype after past dengue increases the chance of severe disease through antibody-dependent enhancement (ADE).

How the diagnosis is made

From returning traveller to a confirmed diagnosis.

The steps a UK GP, A&E team or tropical medicine service will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    Travel and exposure history

    Detailed timeline of travel to endemic areas, mosquito exposure and symptom onset relative to return.

  2. 02

    Assessing

    Clinical examination

    Vital signs, hydration, rash, mucosal bleeding, hepatomegaly and a tourniquet test looking for petechiae.

  3. 03

    Assessing

    Baseline bloodwork

    FBC for thrombocytopenia, leucopenia and haemoconcentration; LFTs; U&Es; LDH; coagulation and D-dimer.

  4. 04

    Confirming

    Antigen and antibody testing

    NS1 antigen day 1 to 7, IgM from day 5, IgG from day 7 or in past infection. RT-PCR confirms and serotypes early.

  5. 05

    Confirming

    Imaging where indicated

    Chest X-ray and ultrasound to look for pleural effusions, ascites and gallbladder wall thickening in plasma leakage.

  6. 06

    Confirming

    Rule out differentials

    Malaria, typhoid, chikungunya, Zika, leptospirosis and rickettsial infections all mimic dengue and need exclusion.

  7. 07

    Escalating

    Notify and refer

    Notify UK Health Security Agency (UKHSA) and involve specialist tropical medicine services early where severity warrants.

Typical timeline: assessment and a confirmed diagnosis within days of presenting.

Symptoms

What dengue actually feels like.

A classic pattern of high fever, severe pain and rash - and the warning signs that mean it is time to attend hospital.

  • Sudden high fever

    Abrupt onset of fever up to 40C, often with chills, marking the start of the 3 to 7 day febrile phase.

  • Retro-orbital and body pain

    Severe headache, pain behind the eyes and marked myalgia and arthralgia earn dengue its nickname of "break-bone fever".

  • Rash and flushing

    Facial flushing early, then a maculopapular rash with characteristic "islands of white in a sea of red".

  • Nausea and vomiting

    Gastrointestinal symptoms are common and can drive dehydration, especially in children and older travellers.

  • Warning signs

    Abdominal pain, persistent vomiting, mucosal bleeding, lethargy, hepatomegaly and rising haematocrit with falling platelets.

  • Critical phase

    Around defervescence (day 4 to 6) plasma leakage may cause hypotension, effusions and dengue shock syndrome.

  • Recovery phase

    Reabsorption of extravasated fluid, gradual improvement and often a second convalescent rash with itch.

  • Red flag - severe dengue

    Shock, severe bleeding or organ failure (liver, heart, kidneys, brain) needs urgent hospital and tropical medicine input.

Treatment

How dengue is treated in the UK.

Supportive care and careful fluid balance for most, hospital and ICU for severe disease - and, for repeat travellers, the Qdenga vaccine.

  • Supportive care only

    There is no specific antiviral for dengue. Rest, oral fluids and paracetamol are the mainstay for uncomplicated disease.

  • Avoid NSAIDs and aspirin

    They increase the risk of bleeding and gastritis during dengue and must be avoided throughout illness.

  • Home management (mild)

    Oral rehydration, daily review, temperature and warning-sign monitoring, and clear safety-netting on when to attend hospital.

  • Hospital admission

    Any warning sign warrants admission for IV isotonic crystalloid, close vital-sign monitoring, haematocrit tracking and urine output review.

  • ICU and severe dengue

    Aggressive but titrated fluid resuscitation, selective colloids, blood products for bleeding and organ support for shock or failure.

  • Blood and platelet products

    Used to treat clinically significant bleeding, not prophylactically for low platelet counts alone.

  • Bite prevention

    DEET, Picaridin or IR3535 repellents, long sleeves, permethrin-treated clothing and air-conditioned or screened accommodation during daytime.

  • Vaccination (Qdenga)

    Qdenga (TAK-003) is a 2-dose vaccine approved in the UK from age 4, offered through specialist travel clinics rather than routinely on the NHS.

What this guide is based on

The sources behind every claim on this page.

WHO guidance, UK surveillance and specialist travel medicine standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

If you have a fever after travel to an area where dengue circulates, seek medical review the same day.

  • World Health Organization. Dengue guidelines for diagnosis, treatment, prevention and control.

  • UK Health Security Agency (UKHSA). Dengue: guidance, data and analysis.

  • NaTHNaC / TravelHealthPro. Dengue country and disease information.

  • European Medicines Agency. Qdenga (TAK-003) product information.

Red flags

When dengue needs urgent attention.

Most dengue is self-limiting. These are the features that mean it is not - and where hospital admission and specialist tropical medicine input are needed.

  • Severe abdominal pain

    A key warning sign of plasma leakage or gastrointestinal bleeding. Needs same-day hospital assessment during dengue illness.

  • Persistent vomiting

    Prevents oral rehydration and often precedes clinical deterioration. Attend hospital for IV fluids and observation.

  • Mucosal bleeding

    Gum bleeding, epistaxis, haematuria, per-vaginal bleeding or melaena all point to severe dengue and demand urgent review.

  • Lethargy or restlessness

    A change in mental state during defervescence can herald dengue shock syndrome. Attend hospital immediately.

  • Cold, clammy extremities

    Signs of shock in a returning traveller with fever should be treated as severe dengue until proven otherwise.

  • Rising haematocrit, falling platelets

    A rapid haemoconcentration with a platelet nadir signals plasma leakage. Admit for close monitoring and fluid resuscitation.

  • Pregnancy or infancy

    Both groups are at higher risk of severe disease and complications. Low threshold for admission and specialist input.

  • Second dengue infection

    A different serotype after past infection increases the chance of severe dengue through antibody-dependent enhancement.

  • Co-morbidities

    Diabetes, renal, cardiac or haematological disease raises complication risk and lowers the threshold for admission.

Living with it

A travellers illness - largely preventable.

Four things that make the biggest difference before, during and after a trip - bite avoidance, vaccine planning, rest during the critical phase and vigilance for second infections.

A quiet reminder

Any fever after travel deserves a same-day review.

Malaria and dengue can look alike early on. Do not wait to see how things develop if you have recently returned from an endemic country.

  1. 01 Prevention

    Bite avoidance first

    Aedes mosquitoes bite by day. Use DEET-based repellent, cover skin and sleep somewhere screened or air-conditioned.

  2. 02 Vaccine

    Ask about Qdenga

    For repeat travellers to endemic regions, discuss Qdenga at a specialist travel clinic before your next trip.

  3. 03 Recovery

    Rest through defervescence

    The critical phase begins as fever falls. Take it slowly, keep fluids up and attend hospital if warning signs appear.

  4. 04 Repeat

    Second infections can be worse

    If you have had dengue before, seek early medical review for any fever after travel to an endemic country.

Frequently asked

Everything we get asked about dengue.

Quick answers on transmission, diagnosis, treatment and the Qdenga vaccine for UK travellers.

  • What is dengue fever?

    Dengue is a viral illness spread by Aedes mosquitoes, caused by one of four related dengue viruses. Most people have a mild febrile illness, but a minority develop severe dengue with plasma leakage, bleeding and shock.

  • Can I catch dengue in the UK?

    At present dengue is only seen in the UK as an imported infection in returning travellers, with no sustained local transmission. However, the mosquito Aedes albopictus is spreading in Southern Europe and cases in Italy, France and Spain in 2024 show the picture is changing.

  • How is dengue diagnosed?

    Through a combination of travel history, clinical features and laboratory tests. NS1 antigen and RT-PCR are useful in the first week, while IgM and IgG antibodies help later. Blood tests also track platelets, haematocrit and liver function.

  • How is dengue treated?

    There is no specific antiviral. Care is supportive with rest, oral fluids and paracetamol for mild cases. NSAIDs and aspirin must be avoided. Anyone with warning signs is admitted for IV fluids and monitoring, and severe dengue is managed in an intensive care setting.

  • Is the Qdenga vaccine available in the UK?

    Yes. Qdenga (TAK-003) is licensed in the UK for people aged 4 and over, whether or not they have had dengue before. It is not routinely funded on the NHS but is offered by specialist travel clinics as a 2-dose course, 3 months apart.

  • How can I avoid dengue when travelling?

    Use an effective repellent (DEET, Picaridin or IR3535), wear long sleeves and trousers, treat clothing with permethrin, and sleep in air-conditioned or well-screened accommodation. Aedes mosquitoes bite through the day, especially early morning and late afternoon.

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