Dengue Fever — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Dengue fever is a mosquito-borne viral illness caused by any of four dengue virus serotypes (DENV 1–4) belonging to the Flaviviridae family, transmitted primarily by the Aedes aegypti mosquito and, to a lesser extent, Aedes albopictus. It is the world's most rapidly spreading tropical disease — approximately 390 million infections occur annually in 129 countries across Asia, the Americas, Africa, and increasingly Europe, causing an estimated 21,000 deaths per year. Dengue clinical spectrum ranges from asymptomatic (75% of infections) to undifferentiated febrile illness, classic dengue fever, dengue haemorrhagic fever (DHF), and dengue shock syndrome (DSS). A second dengue infection with a different serotype carries particularly high risk of severe disease (antibody-dependent enhancement — ADE). Dengue is now considered a global pandemic — over 100 countries are affected, with 390 million infections per year according to WHO estimates, making it the most rapidly spreading vector-borne disease worldwide. No specific antiviral therapy exists; early recognition of warning signs and appropriate fluid management are the critical determinants of outcome.

Dengue is transmitted through bites of infected female Aedes aegypti mosquitoes (the primary vector — a day-biting species, breeding in clean standing water — flower vases, containers, tyres). Aedes albopictus (tiger mosquito) transmits dengue less efficiently but is expanding into temperate regions including Southern Europe. The virus undergoes an extrinsic incubation period of 8–12 days in the mosquito before becoming transmissible. Humans are the primary host — no animal reservoir for DENV 1–4 dengue (unlike sylvatic dengue strains). Risk factors for infection: living or travelling to endemic regions (Southeast Asia, Indian subcontinent, Latin America, Pacific Islands, Caribbean), rainy season (peak mosquito breeding), urban overcrowding with inadequate water storage management. Risk factors for severe dengue: second dengue infection with a different serotype (ADE — most significant risk); prior dengue with dengue haemorrhagic fever; chronic diseases (diabetes, hypertension, renal disease); pregnancy; infants; and age >65.

Incubation period: 4–10 days. Classic dengue fever (dengue without warning signs): sudden high fever (38.5–40°C), severe headache, retro-orbital eye pain (characteristic), myalgia and arthralgia ('breakbone fever' — severe bone and joint pain), facial flushing, nausea, vomiting, macular rash (appears day 3–5). Febrile phase (days 1–3): high fever, positive tourniquet test (petechiae from minor pressure). Critical phase (days 4–6): fever defervescence with risk of plasma leakage — THIS IS THE MOST DANGEROUS PHASE. Warning signs indicating severe dengue: abdominal pain/tenderness, persistent vomiting, clinical fluid accumulation (ascites, pleural effusion), mucosal bleeding (gum bleeding, haematemesis, melaena), lethargy, liver enlargement >2 cm, rising haematocrit with rapid platelet fall. Dengue haemorrhagic fever: plasma leakage causing haemoconcentration (haematocrit rise ≥20%), thrombocytopenia (<100,000/µL), and haemorrhage. Dengue shock syndrome: profound hypotension from severe plasma leakage — life-threatening.

Clinical diagnosis in endemic regions during febrile phase, supplemented by laboratory confirmation. Dengue NS1 antigen test: highly sensitive in first 5 days of illness (detects viral protein — sensitivity 90%+ in days 1–3); rapid immunochromatographic tests available for point-of-care use. RT-PCR: gold standard for viral detection (days 1–5), identifies serotype. IgM/IgG dengue serology: IgM positive from day 5 onwards; useful after the febrile phase; IgG indicates prior infection (secondary infection increases severe disease risk). Full blood count (FBC): progressive thrombocytopenia (platelet <100,000/µL — characteristic but not specific) and rising haematocrit (haemoconcentration from plasma leakage — critical warning sign). Liver function: elevated AST/ALT (hepatitis common in dengue). Ultrasound: detects pleural effusion and ascites in patients with warning signs. Monitoring: daily FBC during critical phase — platelet count and haematocrit trends are the most important clinical parameters.

No specific antiviral treatment exists for dengue. Management is supportive and depends on clinical classification. Dengue without warning signs (outpatient management): paracetamol 1 g every 6 hours for fever and pain (maximum 3 g/day in liver disease); AVOID aspirin and NSAIDs (ibuprofen, diclofenac) — increase bleeding risk due to antiplatelet effects and may worsen thrombocytopenia. Oral hydration: encourage fluid intake of at least 2.5 litres/day (water, oral rehydration solution, fresh fruit juices — avoid caffeinated drinks). Rest. Daily monitoring: platelet count and haematocrit. Dengue with warning signs (hospital admission): IV fluid resuscitation — crystalloid (normal saline or Ringer's lactate) at careful titration to maintain urine output 0.5–1 mL/kg/hr; haematocrit monitoring every 4–6 hours guides fluid decisions. Avoid excess fluid — fluid overload causes pulmonary oedema. Dengue shock syndrome: immediate aggressive fluid resuscitation (10–20 mL/kg rapid bolus); colloid if haematocrit remains high after crystalloid; close haemodynamic monitoring; ICU care. Platelet transfusion: NOT recommended prophylactically — indicated only for active significant bleeding with platelets <20,000/µL. Dengue vaccines: Dengvaxia (CYD-TDV) approved for seropositive individuals aged 9–45 in endemic countries; TAK-003 (QDenga) approved in EU, Indonesia, Thailand, and Brazil for ages 4–60 — 80% efficacy against hospitalisation across serotypes.

While most dengue infections are self-limiting, a subset of patients — particularly those with a second serotype infection — develop severe complications. Dengue haemorrhagic fever (DHF) is defined by plasma leakage causing haemoconcentration (haematocrit rise above 20%), thrombocytopenia below 100,000/µL, and evidence of bleeding; it reflects severe vascular permeability and can progress rapidly during the critical phase (days 4–6). Dengue shock syndrome (DSS) — severe DHF with profound hypotension and circulatory failure — carries mortality of 1–5% even with treatment and up to 40% without fluid resuscitation. Massive haemorrhage from severe thrombocytopenia and coagulopathy can involve the gastrointestinal tract (haematemesis, melaena), respiratory tract (haemoptysis), or intracranially (catastrophic haemorrhagic stroke). Expanded dengue syndrome involves unusual organ involvement: acute hepatic failure (dengue hepatitis with ALT/AST elevation), acute kidney injury, encephalitis and seizures (dengue encephalopathy), myocarditis, and acute respiratory distress syndrome (ARDS). Post-dengue fatigue — prolonged weakness, lethargy, and depression lasting weeks after acute infection — is common and can affect return to work and normal activities. Mortality in severe dengue ranges from less than 1% with expert fluid management to over 20% in resource-limited settings without access to intensive care, highlighting the critical importance of recognizing warning signs and accessing hospital care promptly.

Vector control is the primary prevention strategy: eliminate Aedes mosquito breeding sites — remove all standing water from containers, vases, tyres, and blocked gutters; cover water storage containers; use larvicide (Bacillus thuringiensis israelensis — BTI) in containers that cannot be emptied. Personal protection: apply DEET (≥30%) or picaridin-based repellent to exposed skin; wear long-sleeved, light-coloured clothing; use insecticide-treated bed nets; install window and door screens. Air conditioning reduces indoor mosquito presence. Dengue vaccination: TAK-003 (QDenga) is recommended for travel to endemic areas and for high-risk individuals in endemic regions — does not require prior dengue seropositivity (unlike Dengvaxia). Biological control: release of Wolbachia-infected Aedes aegypti mosquitoes (World Mosquito Programme) reduces dengue transmission by >70% in trials — now deployed in Colombia, Brazil, Indonesia, Australia, and Vietnam.

Go to hospital immediately for any of the following dengue warning signs — these indicate impending critical phase: severe abdominal pain or tenderness; persistent vomiting (3 or more times in 1 hour); bleeding from gums, nose, or in the urine or stool; blood in vomit; sudden improvement in symptoms followed by rapid deterioration; extreme fatigue, restlessness, or confusion; cold or clammy skin (signs of shock). Seek medical review within 24 hours if you have been to a dengue-endemic region within 2 weeks and develop fever with severe headache and eye pain. All dengue patients need daily monitoring — if platelet counts are falling rapidly, hospital admission is required even without warning signs.