Dengue fever is a mosquito-borne viral infection transmitted through the bite of an infected Aedes mosquito. It is one of the most common infectious illnesses in Singapore and across the tropics.
Most people who contract dengue experience a self-limiting febrile illness that resolves within a week to ten days. In a small proportion of cases, however, dengue progresses to a more serious condition — severe dengue, sometimes called dengue haemorrhagic fever or dengue shock syndrome — which can become life-threatening within hours if not recognised and managed promptly.
Because dengue is endemic in Singapore and outbreaks recur seasonally, understanding how the illness progresses, which symptoms require urgent attention, and when to seek medical review is essential for both residents and visitors.
Dengue is caused by one of four related dengue virus serotypes (DENV-1, DENV-2, DENV-3, and DENV-4), transmitted by the bite of an Aedes aegypti or Aedes albopictus mosquito that has previously fed on an infected person. The mosquito becomes infectious after biting a person during their viraemic period and can then pass the virus on to others it bites over its lifespan. Dengue does not spread directly from person to person.
Once in the bloodstream, the virus infects white blood cells and replicates, triggering an immune response that produces the fever, body aches, and rash typical of the illness. The virus also affects the small blood vessels and the platelets and clotting factors that keep them intact — this is the mechanism behind the bleeding tendency and vascular leakage seen in more severe cases.
You can lower your risk of dengue by avoiding mosquito bites and to take steps to reduce the mosquito population in your area.
Dengue follows a recognisable clinical course. Understanding which phase a patient is in matters more than the day count alone, because the critical phase — when complications are most likely — often begins just as the fever appears to be improving.
What happens: Sudden high fever (often up to 40°C), severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, and a flushed skin or fine rash. Most symptoms in this phase are managed with rest, fluids, and paracetamol.
What happens: The most dangerous window. As body temperature drops, plasma can leak from blood vessels and platelet counts can fall sharply. Most patients do not develop complications here, but this is the period when warning signs of severe dengue — persistent vomiting, abdominal pain, bleeding, or restlessness — must be watched for closely.
What happens: Fluid that leaked into the tissues is reabsorbed, platelet counts recover, and energy gradually returns. A fine, itchy rash and a feeling of fatigue are common during this stage and typically resolve over one to two weeks.
Symptoms vary widely, from a mild, flu-like illness to a more severe presentation with bleeding and shock. Many infections, particularly in children, are so mild they go unnoticed.
These typically appear as the fever begins to settle, around days 3 to 7 of illness, and warrant same-day medical review:
A smaller number of patients progress to severe dengue, characterised by significant plasma leakage, bleeding, or organ impairment. This requires close inpatient monitoring and, in some cases, intensive care. Second infections, young children, older adults, and pregnant women carry a higher risk of progressing to this stage.
Diagnosis combines a travel and exposure history, symptom assessment, and laboratory testing. The choice of test depends on how many days a patient has been unwell, since the virus and the body's antibody response become detectable at different points in the illness.
There is currently no vaccine recommended for general dengue prevention in Singapore. Dengvaxia, the only dengue vaccine approved locally, is limited to individuals aged 12 to 45 who have had a confirmed prior dengue infection, since vaccinating someone without prior exposure can raise their risk of severe disease if they are later infected. Prevention therefore continues to rely on avoiding mosquito bites and reducing mosquito breeding grounds.
