Dengue Fever

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Dengue fever is a self-limiting flu-like illness that is caused by the dengue virus (a type of flavivirus).

Dengue fever is typically spread by the mosquito Aedes aegypti which is common in the tropics worldwide, especially Southeast Asia, Africa, the Pacific and the Americas.1 It is less commonly spread by Aedes albopictus.2

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There are four serotypes of the dengue virus: DEN-1, DEN-2, DEN-3 and DEN-4.

Those who are infected by the dengue virus develop life-long immunity.2 However, individuals with previous immunity to one serotype infected with another serotype can develop severe dengue.1

The incubation period of dengue fever is usually two to seven days. There are three phases of dengue fever: febrile phase, critical phase and recovery phase.1

Risk factors

Risk factors for contracting dengue fever include:3

  • Living or travelling to dengue-endemic areas
  • Poor public hygiene
  • High population density

Clinical features

The clinical features of dengue fever differ according to the phase of the disease.Β 

Febrile phase

The febrile phase usually lasts two to seven days.


Typical symptoms of the febrile phase include:

  • High-grade fever
  • Maculopapular rash
  • Facial flushing
  • Muscle and joint pains
  • Severe headache
  • Retro-orbital pain
  • Nausea or vomiting

Clinical examination

Typical findings on clinical examination include:

  • Maculopapular rash sparing palms and soles (Figure 1)
  • Positive tourniquet test: inflate blood pressure cuff on upper arm for five minutes; a positive test is when there is >20 petechiae per 2.5cm.2
Maculopapular rash of dengue fever
Figure 1. Maculopapular rash of dengue fever

Critical phase

The critical phase usually happens after the third day of fever and lasts for 24 to 48 hours. There is an increase in capillary permeability with a drop in body temperature.


Typical symptoms of the critical phase include:

  • Severe abdominal pain
  • Persistent vomiting
  • Rapid breathing
  • Lethargy
  • Altered consciousness level
  • Restlessness

Clinical examination

Signs of non-severe dengue include:

  • Maculopapular rash sparing palms and soles
  • Positive tourniquet test

Important signs to not miss out which may indicate dengue with warning signs include:

  • Haemorrhagic manifestations: petechiae, mucosal membrane bleeding and menorrhagia
  • Enlarged and tender liver
  • Evidence of shock: prolonged capillary refill time

Signs that indicate severe dengue include:

  • Clinical fluid accumulation: pleural effusion and ascites
  • Periorbital oedema
  • Hypovolaemic shock
  • Severe bleeding

Recovery phase

During the recovery phase, the leaked plasma is reabsorbed into the bloodstream. The individual generally improves in the following 48 to 72 hours.

Clinical examination

Some patients may develop a rash known as β€œisles of white in a sea of red” which indicates recovery (Figure 2).3

Dengue fever rash "Isles of White in a Sea of Red"
Figure 2. β€œIsles of white in a sea of red” indicating recovery phase.


The severity of dengue is classified using the WHO Dengue Classification 2009 (Table 1).

Table 1. The classification of severity for dengue fever.

Probable dengue

Dengue with warning signs

Severe dengue

1. Live in or travel or travel to dengue-endemic areas

2. Fever

3. Two of the following criteria:

  • Nausea, vomiting
  • Rash
  • Aches and pains
  • Positive tourniquet test
  • Leukopaenia
  • Any warning sign


1. Abdominal pain

2. Persistent vomiting

3. Clinical fluid accumulation

4. Mucosal bleed

5. Lethargy

6. Restlessness

7. Tender liver

8. Increase in haematocrit with a rapid decrease in platelet count

1. Severe plasma leakage:

  • Dengue shock syndrome
  • Fluid accumulation with respiratory distress

2. Severe haemorrhage

3. Severe organ impairment:

  • Liver impairment
  • Central nervous system impairment
  • Cardiac failure

Differential diagnoses

Possible differential diagnoses in the context of suspected dengue fever include:3


Bedside investigations

Relevant bedside investigations in the context of dengue fever include:

  • Blood pressure: hypotension may result from dengue shock syndrome

Laboratory investigations

Relevant laboratory investigations in the context of dengue fever include:

  • FBC: raised haematocrit and low platelet count suggests dengue with warning signs (may also present with neutropenia and leukopenia)
  • LFTs: raised ALT and AST suggests severe dengue with organ involvement
  • U&Es: there may be electrolyte imbalance due to persistent vomiting
  • Coagulation screen: may reveal prolonged APTT and PT


Relevant imaging investigations in the context of dengue fever include:

  • Chest X-ray: to assess for pleural effusion

Other investigations

Diagnostic tests that may be used to confirm dengue fever include:3,4

  • NS1 antigen test: detected in first 4 days of illness
  • IgM antibodies with ELISA: detected after 5 days of illness and peaks 2 weeks after onset of symptoms
  • IgG antibodies with ELISA: detected after 7 days of illness and lasts for life (used to confirm secondary infection)


Initial management

Most dengue patients do not need hospital admission and there is no specific treatment for dengue fever.

However, patients must be evaluated for warning signs and the possibility of developing severe dengue. Key points of management include:

  • Controlling fever with paracetamol
  • Notifying Public Health England
  • IV fluid resuscitation with close monitoring to prevent fluid overload
  • Escalation of patients with warning signs and severe dengue to a secondary health care facility


Some steps that can be taken to prevent dengue fever especially during travel include:5

  • Wearing long-sleeved clothes
  • Spraying insect repellent
  • Removing any sources of breeding sites


Potential complications of dengue fever include:3

  • Dengue haemorrhagic fever
  • Disseminated intravascular coagulation
  • Dengue shock syndrome
  • Severe organ involvement (e.g. cardiac failure, liver impairment)

Key points

  • Dengue fever is a self-limiting flu-like illness that is caused by the dengue virus.
  • Dengue fever has three phases: febrile phase, critical phase and recovery phase.
  • The severity of dengue fever can be divided into non-severe dengue, non-severe dengue with warning signs and severe dengue.
  • Laboratory investigations including FBC, LFTs and U&Es as well as diagnostic tests for dengue should be carried out if dengue is suspected.
  • Dengue is a self-limiting illness and patients are usually admitted if they develop warning signs or severe dengue.
  • Complications of developing dengue fever include dengue haemorrhagic fever, dengue shock syndrome, disseminated intravascular coagulation and organ impairment.


Professor Edmund Ong Liang Chai

Consultant Physician in Infectious Diseases


Dr Chris Jefferies


  1. Ralston, S. H., Penman, I. D., Strachan, M. W. J., & Hobson, R. (Eds.). Davidson’s principles and practice of medicineΒ (23rd ed.). Published in 2018. Elsevier Health Sciences.
  2. UpToDate. Dengue virus infection: Clinical manifestations and diagnosis. Published in 2021. Available from: [LINK]
  3. Dengue. Published in 2016. Available from: [LINK]
  4. World Health Organization. Dengue: guidelines for diagnosis, treatment, prevention and control. Published in 2009. Available from: [LINK]
  5. World Health Organization. Dengue and severe dengue. Published in 2021. Available from: [LINK]

Image references

  1. United States Military. Dengue rash. Licence: [Public Domain]
  2. Ranjan Premaratna. Dengue recovery rash (White islands in red sea). Licence: [CC BY-SA]


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