Dengue Fever

Dengue Fever

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Dengue fever is an infectious, self-limiting flu-like illness caused by the dengue virus (a type of flavivirus). It is usually spread by the mosquito Aedes aegypti, found in the tropics worldwide, particularly Southeast Asia, Africa, the Pacific and the Americas.1 Less commonly, Aedes albopictus is a source of transmission.2


There are four serotypes of the dengue virus, DEN-1, DEN-2, DEN-3 and DEN-4. People exposed to the virus have lifelong immunity.2 However, if someone with immunity to one serotype is infected with another, they can experience severe dengue.1 The incubation period usually lasts two to seven days, with three phases - the febrile phase, critical phase and recovery phase.1

Risk factors

Factors that increases one's chances of contracting dengue fever include living or travelling to dengue-endemic areas, poor public hygiene, and high population density.3

Clinical features

The symptoms of dengue fever vary according to the phase of the disease.

Febrile phase

The febrile phase typically lasts two to seven days.


Common symptoms during the febrile phase include: high-grade fever, maculopapular rash, facial flushing, muscle and joint pains, severe headache, retro-orbital pain and nausea or vomiting.

Clinical examination

Typical findings on clinical examination include: maculopapular rash (not present on palms and soles) and a positive tourniquet test (>20 petechiae per 2.5cm when inflated blood pressure cuff is applied for five minutes).2

Critical phase

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

Dengue Classification and Symptoms

Dengue is classified using the World Health Organization Dengue Classification 2009 (Table 1). It consists of three categories: probable dengue, dengue with warning signs, and severe dengue.

Typical Symptoms of the Critical Phase

Common symptoms of the critical phase include:

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

Signs of Non-Severe Dengue

Signs of non-severe dengue include:

  • Maculopapular rash sparing palms and soles
  • Positive tourniquet test

Signs to Not Miss Out

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

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. Some patients may develop a rash known as “isles of white in a sea of red” which indicates recovery.


The severity of dengue is classified using the WHO Dengue Classification 2009 (Table 1). It consists of three categories: probable dengue, dengue with warning signs, and severe dengue.

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


Severe Organ Impairment

Possible types of severe organ impairment associated with dengue fever include:

  • Liver impairment
  • Central nervous system impairment
  • Cardiac failure

Differential Diagnoses

In the context of suspected dengue fever, the possible differential diagnoses include:

  • Malaria
  • Typhoid fever
  • HIV seroconversion
  • Infectious mononucleosis
  • Measles
  • Erythema infectiosum
  • Chikungunya
  • Zika virus
  • COVID-19


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:

  • 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:

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


Potential complications of dengue fever include:

  • 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 such as Full Blood Count (FBC), Liver Function Tests (LFTs) and Urine and Electrolytes (U&Es) as well as diagnostic tests should be carried out if dengue is suspected. Dengue is a self-limiting illness and patients are usually admitted if they show warning signs or severe dengue. Complications of developing dengue fever include dengue haemorrhagic fever, dengue shock syndrome, disseminated intravascular coagulation and organ impairment.

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