Dengue

Synonyms: breakbone fever, dengue fever, dengue haemorrhagic fever, dengue shock syndrome, dandy fever, seven-day fever, duengero, ki denga pepo (Swahili, meaning 'sudden overtaking by a spirit')

See also the separate Viral haemorrhagic fevers article.

What is dengue?¹

Dengue is a highly infectious disease of tropical countries and is rapidly becoming a global burden. It is the most prevalent arthropod-transmitted viral disease worldwide.²

The dengue virus is transmitted to humans through the bite of infected mosquitoes. Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus. These mosquitoes are also vectors of chikungunya, yellow fever, and Zika viruses. Human-to-human direct spread is rare but has occasionally been reported via perinatal transmission, blood transfusion, organ transplantation, and, exceedingly rarely, sexual transmission.²

In order for transmission to occur, the mosquito must feed on a person during the five-day period when large amounts of virus are in the blood; this period usually begins before the person becomes symptomatic. After entering the mosquito, the virus will require an additional 8-12 days of incubation before it can then be transmitted to another human. The mosquito remains infected for the remainder of its life, which might be days or a few weeks.³

Dengue is caused by a virus of the Flaviviridae family. The virus responsible for causing dengue, is called dengue virus (DENV). There are four distinct serotypes of the virus that cause dengue (DENV-1, DENV-2, DENV-3, and DENV-4).

Infection by any of the four serotypes may range from asymptomatic to life-threatening. The pathological effects are immune-mediated. The development of severe disease seems to involve a complex interplay of host immunity and genetic predisposition combined with certain viral virulence factors.⁴

Dengue is rarely diagnosed in the UK. However, Dengue is an important cause of fever in returning travellers. It should be on the differential diagnosis of travellers with unexplained pyrexia returning from an affected area. It should rise higher on the list of differential diagnosis if there are features suggesting bleeding, hypovolaemia, increased vascular permeability, or organ failure.

Classification of dengue⁵

Dengue is a single disease with several different clinical presentations. In 2009 the World Health Organization (WHO) revised the classification according to levels of severity:

Dengue without warning signs
Fever and two of the following:

• Nausea, vomiting.

• Rash.

• Aches and pains.

• Leukopenia.

• Positive tourniquet test.

• Laboratory-confirmed dengue.

With ability:

• To tolerate adequate volumes of oral fluid replacement.

• To pass urine at least once every six hours.

Dengue with warning signs
Patients with at least one of the following warning signs:

• Abdominal pain or tenderness.

• Persistent vomiting.

• Clinical fluid accumulation.

• Mucosal bleed (gingival bleeding, epistaxis, conjunctival bleeding, haematemesis, melaena, fresh blood per rectum, haematuria, or vaginal bleeding).

• Lethargy/restlessness.

• Liver enlargement >2 cm.

• Increased haematocrit with concurrent decrease in platelet count (100,000 platelets/mm³ or less).

OR: at least one comorbid condition such as pregnancy, infancy, old age, diabetes mellitus, renal failure.
OR: social circumstances such as living alone or living far from hospital.

Severe dengue fever
Patients with any of the following features: Severe plasma leakage leading to:

• Shock.

  • Fluid accumulation leading to respiratory distress.

• Severe bleeding as evaluated by the clinician.

• Severe organ involvement:

  • Liver: AST or ALT above 1000 IU/L.

  • Impaired consciousness.

  • Heart and other organs.
    
    Some argue that the definitions need to be more specific, so classification may evolve further.

Dengue epidemiology¹

• The global incidence of dengue has grown dramatically since the middle of the 20th century and continues to do so.² The global burden of dengue fever has doubled since 1990.²

• At least one half of the global population is estimated at risk of infection and an estimated 390 million people are infected each year.⁶ Of these, 58 to 59 million are symptomatic, with reported mortality ranging from 13,500 to more than 40,000 deaths per year.²

• Dengue is endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. The Americas, Southeast Asia, and the Western Pacific regions are the most seriously affected. There are increasing reports of dengue fever infections in temperate regions where the affected person has no history of travel.²

• There are two typical patterns of transmission - epidemic transmission and hyperendemic transmission. Epidemic transmission occurs where a single DENV serotype is introduced into a largely susceptible population whereas hyperendemic transmission occurs where there is continuous circulation of multiple serotypes within the same geographic area. This is most common in urban areas and is associated with more severe disease.²

• Between 2010 and 2014, there were an average of 350-400 imported cases of dengue fever in England, Wales, and Northern Ireland each year.⁷ There were 71 reported cases in the first 3 months of 2025.⁸All were found in people who had recent travel to higher-risk areas.

• The highest risks of death from dengue fever are in South-East Asia, South Asia, and Latin America.²

Risk factors¹

For contracting dengue virus

• High population density.

• Urban living.

• Poor public hygiene.¹

• Exposure to mosquitoes in endemic areas.

For developing severe dengue

• Age - 95% of severe dengue occurs in the those aged under 15 years.

• Repeated dengue infections - infection with a secondary serotype is a risk factor for the development of severe disease.

• Genetic factors - disease severity and outcome appear related to variation at multiple gene loci involved in immune response.⁹

• Viral genotypes - some strains may be more virulent.

• Nutritional status - children who are overweight have been shown to be at increased risk of developing severe dengue fever.¹⁰

Dengue symptoms¹¹¹

80% of dengue infections are asymptomatic and 90% of those which are symptomatic result in only mild disease. Symptomatic dengue tends to cause symptoms starting between 4 and 10 days after the mosquito² bite and lasting around 3-7 days. Mild symptoms include:

• High fever (>40℃).

• Severe headache.

• Pain behind the eyes.

• Muscle and joint pains.

• Nausea and vomiting.

• Swollen glands.

• Rash (typically morbilliform or confluent, occasionally petechial).

Severe dengue

Severe dengue is more common on the second or subsequent infection. The symptoms usually develop after the initial feverish phase has passed and can include:

• Severe abdominal pain.

• Persistent vomiting.

• Tachypnoea.

• Bleeding gums or nose.

• Fatigue.

• Restlessness.

• Haematemesis or bloody stool.

• Excessive thirst.

• Pallor.

• Cold skin.

• Weakness.

Severe dengue requires immediate medical attention. Hospitalisation is often required due to the risks of severe organ impairment, haemorrhage, fluid overload, and shock.

Recovery

Fatigue may last for several weeks after the illness, particularly in adults. Severe itching and bradycardia are common during recovery. There may be another rash which may be maculopapular or vasculitic, followed by peeling of the skin.

Differential diagnosis

There is a long list of differential diagnoses, including many causes of febrile illness, of flu-like illness, and of shock. A careful history will rule some conditions out.

• Malaria.

• Typhoid fever.

• Typhus.

• Scrub typhus.

• HIV seroconversion.

• Infectious mononucleosis.

• Coxsackievirus and other enteroviruses.

• Rickettsial infections.

• Measles.

• Rubella.

• Parvovirus B19.

• Weil's disease (leptospirosis).

• Influenza.

• Chikungunya viral infection.

• Kawasaki disease.

• Yellow fever.

• Hantavirus.

• Other viral haemorrhagic infections.

• Meningococcal septicaemia.

• Encephalitic viruses - eg, West Nile virus.

Severe dengue

As above, plus any cause of shock, including sepsis and toxic shock syndrome.

Investigations¹

General

• FBC may show high PCV with low platelets. There may be paradoxical lymphocytosis (>15% circulating white cells) but overall leukopenia.

• Clotting studies can reveal prolongation of APTT and PT. Fibrin degradation products may be elevated.

• U&E may show electrolyte disturbance. LFTs can be elevated - especially AST.

• Severe cases may show reduced bicarbonate due to acidosis.

• Blood cultures and repeated malaria films should be checked in the traveller returning with a high fever.

Specific²

During the first week of illness, the virus may be able to be detected directly by serology. Dengue IgM can be identified from the 4th day of the illness. There can be cross-reactivity with other flaviviruses such as Zika virus, yellow fever or Japanese encephalitis.

Dengue fever treatment and management^{2112 13}

There is no specific treatment for dengue. Patients should rest, stay hydrated, and seek medical advice if symptoms become severe. Depending on the clinical manifestations and other circumstances, patients may be managed at home or require hospitalisation. Supportive care such as anti-pyretics and painkillers can be taken to control the symptoms. Due to the risks of haemorrhage, paracetamol is a better option than NSAIDs.

In severe dengue, treatment may require:

• Intravenous fluid resuscitation with close monitoring, observing for increased capillary permeability.

• High-volume and aggressive colloid/crystalloid infusion.

• Inotropes and renal support.

• Secondary bacterial infections may require treatment.

• Haemorrhage and shock may require FFP and platelets.

Prognosis¹

• Dengue is typically a self-limiting flu-like disease. The vast majority make a full recovery.

• Recovery from infection provides lifelong immunity against that serotype. However, cross-immunity to the other serotypes after recovery is only partial, and temporary. Subsequent infections (secondary infection) by other serotypes increase the risk of developing severe dengue.

• Severe dengue has a mortality rate of 50% if untreated; however, this is reduced to less than 5% if appropriately treated. Medical care by experienced teams decreases mortality rates to less than 1% in majority of the countries.

• Most severe dengue and most deaths occur in children aged under 15 years.

Complications

• Hepatic failure.

• Encephalopathy.

• Myocarditis.

• Disseminated intravascular coagulation.

• Septicaemia.

Prevention of dengue fever¹

There is an ongoing need to adhere to other disease preventative measures such as well-executed and sustained vector control. Individuals, whether vaccinated or not, should seek prompt medical care if dengue-like symptoms occur.

Risk factors

Further mosquito bites should be particularly avoided during the first week of illness. Virus may be circulating in the blood during this time, and there may be transmission of the virus to new uninfected mosquitoes, who may in turn infect other people.

The main method to control or prevent the transmission of dengue virus is to combat the mosquito vectors by:

Individual

• Disposing of solid waste properly and removing artificial man-made habitats that can hold water.

• Covering, emptying and cleaning of domestic water storage containers on a weekly basis.

• Applying appropriate insecticides to water storage outdoor containers.

• Use of personal household protection measures, such as window screens, repellents, coils and vaporisers. These measures must be observed during the day both inside and outside of the home (including at work/school) because the primary mosquito vectors bite throughout the day.

• Wearing clothing that minimises skin exposure to mosquitoes.

Community

• Preventing mosquitoes from accessing egg-laying habitats by environmental management and modification.

• Educating the community on the risks of mosquito-borne diseases.

• Engaging with the community to improve participation and mobilisation for sustained vector control.

• Active monitoring and surveillance of vector abundance and species composition should be carried out to determine effectiveness of control interventions.

• Prospectively monitoring prevalence of virus in the mosquito population, with active screening of sentinel mosquito collections.

• Vector surveillance can be combined with clinical and environment surveillance.

Vaccination against dengue

There is currently only one vaccine available against dengue (QDenga). Worldwide this is recommended for children aged between 6 and 16 years living in high transmission settings.¹ It is available as a private travel vaccine in the UK and can be given from the age of 4 years. There are trials currently taking place to assess other potential vaccines - some of these have reached Phase III trials.¹⁴¹⁵

Dr Mary Lowth is an author or the original author of this leaflet.