Dengue Fever — Symptoms, Warning Signs, NS1 Antigen Test & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Dengue fever is a mosquito-borne viral infection caused by dengue virus (DENV), a single-stranded positive-sense RNA flavivirus with four antigenically distinct serotypes (DENV-1, DENV-2, DENV-3, DENV-4). It is primarily transmitted by Aedes aegypti mosquitoes (also A. albopictus), which bite predominantly during the day (early morning and late afternoon). Dengue is endemic in over 100 tropical and subtropical countries across Southeast Asia, South and Central America, the Pacific, and Africa, affecting approximately 390 million people annually — with only 25% developing symptomatic disease. The WHO classifies dengue into dengue (with or without warning signs) and severe dengue — previously known as dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS). Antibody-dependent enhancement (ADE) of secondary infection with a different serotype is the major mechanism behind severe dengue.

Dengue virus is transmitted by the bite of an infected female Aedes aegypti mosquito — a daytime-biting mosquito that breeds in stagnant water (flower pots, tyres, water storage containers, discarded plastic). Geographic risk: endemic zones — Southeast Asia (India, Indonesia, Thailand, Philippines, Sri Lanka, Bangladesh), Latin America and the Caribbean (Brazil, Colombia, Mexico), Pacific Islands, and sub-Saharan Africa. Risk factors for severe dengue: secondary dengue infection with a different serotype (ADE mechanism — pre-existing cross-reactive antibodies from first infection paradoxically enhance viral uptake into monocytes during second infection, causing greater viral load and more severe disease); age — children (especially under 15 in endemic areas) and the elderly; pregnancy; obesity; genetic factors; and specific serotype combinations (DENV-2 secondary after DENV-1 is particularly associated with severe disease).

Incubation period: 4-10 days after mosquito bite. Febrile phase (days 1-3): sudden high fever (39-40°C), severe headache, retro-orbital pain (pain behind the eyes), severe myalgia and arthralgia ('breakbone fever'), flushed face, nausea and vomiting, rash (diffuse flushing — early; maculopapular rash with islands of white in red — days 3-5). Critical phase (days 4-6 — occurs when fever defervesces): plasma leakage from capillaries (pleural effusion, ascites); thrombocytopaenia (platelet count falls — risk of bleeding); haemoconcentration (rising haematocrit indicating plasma leakage). Dengue warning signs requiring immediate hospitalisation: abdominal pain or tenderness; persistent vomiting; clinical fluid accumulation (ascites, pleural effusion); mucosal bleeding (epistaxis, gum bleeding, haematemesis, melaena); lethargy; liver enlargement greater than 2 cm; rising haematocrit with rapid platelet decline. Recovery phase (days 6-7): reabsorption of leaked fluid — risk of fluid overload if excessive IV fluids given.

NS1 antigen test (non-structural protein 1): rapid diagnostic test — detects dengue NS1 antigen in blood; positive in febrile phase (days 1-5); high sensitivity (70-85%) and specificity (up to 99%) for acute dengue. NS1 ELISA: laboratory-based; higher sensitivity than RDT. RT-PCR for dengue RNA: highest sensitivity; identifies serotype; positive in febrile phase (days 1-5); expensive; confirms diagnosis and guides public health response. Serology (IgM and IgG antibodies): IgM detectable from day 4-5 of illness onwards (peaks at 2 weeks); IgG rises in secondary dengue infection (high IgG early in illness distinguishes secondary from primary infection). Full blood count (daily monitoring): platelets (thrombocytopaenia — platelet count below 100,000/microL is common; below 20,000/microL is severe); haematocrit (haemoconcentration — rising above 20% of baseline indicates plasma leakage); WBC (leucopaenia characteristic of dengue). Liver function tests: elevated ALT and AST common (hepatitis); severe dengue can cause acute liver failure.

There is no specific antiviral treatment for dengue — management is supportive. Dengue without warning signs (outpatient management): rest; oral rehydration (drink adequate fluids to maintain urine output); paracetamol (acetaminophen) only for fever and pain — NEVER use aspirin, ibuprofen, or other NSAIDs (inhibit platelet function, increase bleeding risk); daily monitoring of platelet count and haematocrit; return immediately to hospital if any warning signs develop. Dengue with warning signs or severe dengue (hospitalisation required): IV crystalloid fluid resuscitation (isotonic saline or Ringer's lactate) — titrated carefully to clinical response (urine output 0.5-1 mL/kg/hr, stable haematocrit); close monitoring every 1-4 hours; avoid excessive fluid administration (causes pulmonary oedema during recovery phase). Platelet transfusion: NOT recommended for thrombocytopaenia alone (platelets below 50,000 without active bleeding); only for life-threatening bleeding. Severe dengue with shock: IV fluid boluses (10-20 mL/kg), intensive care monitoring; vasopressors if persistent shock despite fluids. Dengue vaccine (Qdenga — TAK-003, tetravalent live attenuated dengue vaccine): approved in EU, UK, and several endemic countries for ages 4-60; 80% effective against dengue disease regardless of prior dengue serotype status in clinical trials; offered to populations in endemic areas.

Severe dengue (previously dengue haemorrhagic fever/dengue shock syndrome) is a life-threatening emergency with case fatality rates of 1-5% overall and up to 26% in centres without adequate intensive care. Severe plasma leakage causes circulatory failure and dengue shock syndrome (DSS) — hypotension, cold clammy extremities, narrow pulse pressure (below 20 mmHg), tachycardia. Severe bleeding: haematemesis, melaena, pulmonary haemorrhage, intracranial haemorrhage — from severe thrombocytopaenia, coagulopathy, and vascular fragility. Severe organ impairment: acute liver failure (fulminant hepatitis); acute renal failure; acute respiratory failure; severe myocarditis; encephalitis (rare). Without prompt fluid management, dengue shock syndrome carries high mortality. Expanded dengue syndrome: unusual manifestations including acute pancreatitis, myositis, orchitis, and prolonged fatigue — dengue can no longer be considered a simple febrile illness in endemic settings.

Mosquito control is the cornerstone of dengue prevention. Eliminate Aedes breeding sites: remove stagnant water from flower pots, plant saucers, tyres, blocked gutters, and all water containers weekly — this is the single most effective community-level measure. Personal protection: wear long-sleeved clothing and long trousers during the day when Aedes mosquitoes are active; use insect repellent containing DEET (50%), icaridin/picaridin, or IR3535; sleep and rest under mosquito nets or in rooms with air conditioning or fine mesh screens; use permethrin-treated clothing for high-risk areas. Community measures: indoor residual spraying (IRS); insecticide-treated materials; WHO-endorsed biological control using Wolbachia-infected Aedes mosquitoes (reduces dengue virus replication in mosquitoes — deployed in Colombia, Indonesia, Australia). Dengue vaccine (Qdenga): recommended for age 4-60 in endemic countries where dengue is a significant public health burden; two doses 3 months apart. Travellers to endemic areas: register with a travel health clinic; obtain Qdenga vaccine if available and appropriate.

Seek immediate hospital care during the critical phase (when fever subsides — days 4-6) for any dengue warning signs: severe or persistent abdominal pain, persistent vomiting (3 or more times in one hour), bleeding from gums, nose, or in vomit or stools, fluid accumulation (swollen abdomen, difficulty breathing), extreme fatigue or confusion, pale, cold, or mottled skin, or rapid weak pulse. These signs indicate progression to severe dengue requiring IV fluid management. During the febrile phase, see a doctor promptly for confirmation of diagnosis (NS1 test), monitoring of full blood count and platelet trends, and guidance on fluid intake and warning signs to watch for. Travellers returning from dengue-endemic areas with fever within 14 days of return should attend their GP or travel health clinic same-day — dengue must be excluded before attributing fever to other causes. Any fever in a child under 2 years with recent travel to a dengue-endemic area warrants same-day paediatric assessment.