Dengue fever

Overview

Dengue fever is an acute febrile disease caused by the dengue virus. There are four different circulating serotypes of dengue virus (DENV 1 to 4) circulating in the world, including Singapore. Hence, individuals can be infected with dengue up to four times.

Pathogen(s)

Dengue virus, a member of the Flaviviridae family. There are four serotypes (DENV 1, 2, 3, and 4).

Transmission

Transmitted via the bite of an infective Aedes aegypti and Aedes albopictus mosquitoes.

Incubation period: Typically 4 to 7 days; range is 3 to 14 days.

Infectious period: Infectious to mosquitoes from 2 days before, to 5 days after illness onset (when the patient is viraemic).

Clinical features

Dengue fever:

Acute onset of fever which lasts for 2 to 7 days with 2 or more of the following:

• Headache, backache, myalgia

• Rash: maculopapular or flush; petechial with islands of sparing

• Retro-orbital pain

• Bleeding

• Leucopenia

• Thrombocytopenia may also occur and usually worsens when fever resolves

Dengue haemorrhagic fever (DHF)

For a diagnosis of DHF, a case must fulfil all four of the following criteria:

1. Fever

2. Bleeding manifestations (e.g. petechiae, ecchymosis, epistaxis, gum bleeding, haematemesis, or melena)

3. Thrombocytopenia (< 100 X 10⁹/L)

4. Evidence of increased capillary permeability

   1. Haematocrit increased by >20% above baseline

   2. Pleural effusion

   3. Hypoalbuminaemia 

Dengue shock syndrome (DSS)

• For a diagnosis of DSS, all four criteria for DHF must be met, in addition to hypotension, narrowed pulse pressure (< 20 mm Hg) and impaired organ perfusion.

Risk factors

Risk factors include:

• Living in or travelling to Dengue-affected areas

Diagnosis

There are combination tests such as dengue NS1, IgM and IgG available for laboratory diagnosis of dengue.

• NS1 antigen assay (rapid test): Positive for dengue NS1 protein within the first week of onset

• PCR: Positive for dengue virus within 5 days of onset

• Serology: Positive dengue IgM on acute serum sample A high-titre IgG antibody may also be indicative of dengue, particularly secondary infection. IgM antibodies appear on approximately the fifth day of illness and last for 2 months. A 4-fold rise in titres of a pair of acute and convalescent sera is confirmatory.

Treatment and management

• Supportive.

• Paracetamol for fever (avoid non-steroidal anti-inflammatory drugs)

• Intravenous fluids for hypotension and dehydration (avoid over-hydration precipitating pulmonary oedema in DHF)

• Daily platelet and haematocrit measurement when platelets drop below 100,000/mm³

• Complete bed rest for platelet count less than 50,000/mm³

• There is no evidence that prophylactic platelet transfusion (in the absence of bleeding) is beneficial

Precaution, prevention, and control

Standard precautions apply in healthcare settings.

The Health Sciences Authority (HSA) has approved a dengue vaccine, Dengvaxia, for persons aged 12 to 45 years old. This is the only licensed dengue vaccine in Singapore. Dengvaxia can be useful for individual protection for persons in this age range who have been previously infected with dengue.

The vaccine is NOT recommended for those without prior dengue infection. Those with an unknown history of dengue infection should have serology testing prior to vaccination. Individuals interested in getting the vaccine should consult their doctors on the benefits and risks of vaccination.

Vector control remains the mainstay in reducing the spread of mosquito-borne diseases. Individuals can also take precautions against mosquito bites, such as:

• Staying in rooms which are well-screened or air-conditioned

• Wearing long, covered clothing that cover most of your body

• Applying an effective insect repellent, such as those containing DEET, Picaridin or IR3535 as the active ingredient regularly

Notification

Who should notify:

• Medical practitioners

• Laboratories

When to notify:

• On clinical suspicion or laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information. 

Notification timeline:

• As soon as possible. No later than 24 hours from the time of diagnosis.

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the numbers of confirmed dengue cases in Singapore.

National Environment Agency (NEA) website on dengue cases and clusters.