Define Dengue Fever. Describe its classification, clinical features, investigations and management.

Definition

• Dengue is an acute arboviral infection caused by the dengue virus (a flavivirus, 4 serotypes den 1–4), transmitted by the Aedes aegypti mosquito.
• A second infection with a different serotype increases the risk of severe disease (antibody-dependent enhancement).

Phases of Illness

Febrile phase (2–7 days) → Critical phase (around defervescence, days 3–7) — plasma leakage → Recovery phase — reabsorption of fluid

WHO Classification (2009)

Clinical Features

• High fever with severe headache, retro-orbital pain, myalgia and arthralgia ('breakbone fever'), and rash.
• Positive tourniquet test, thrombocytopenia and leucopenia.
• Plasma leakage (pleural effusion, ascites, rising haematocrit) in the critical phase → hypovolaemic shock (dengue shock syndrome).

Investigations

• NS1 antigen (positive early, days 1–5); IgM/IgG serology (after day 5).
• CBC — thrombocytopenia, leucopenia, and a rising haematocrit (a key marker of plasma leakage).
• Serial monitoring of haematocrit, platelets and warning signs.

Management

• No specific antiviral — treatment is supportive, centred on careful fluid management.
• Isotonic crystalloid for those with warning signs/leakage, titrated to the haematocrit and vital signs (avoid both under- and over-hydration).
• Paracetamol for fever; avoid aspirin and NSAIDs (bleeding risk).
• Platelet transfusion only for significant bleeding — not for a low count alone.
• Manage dengue shock syndrome with prompt fluid resuscitation.

Older (DHF/DSS) Grading

Pathophysiology of Severe Dengue

Immune activation increases vascular permeability, causing plasma leakage (into pleural/peritoneal spaces), haemoconcentration and hypovolaemic shock; thrombocytopenia and coagulopathy contribute to bleeding — hence the emphasis on monitoring haematocrit and careful fluid therapy.

Criteria for Discharge

• Afebrile > 24–48 h without antipyretics, improving clinically and appetite returning.
• Rising platelet trend, stable haematocrit, and no respiratory distress from effusions/ascites.

Tourniquet Test

A blood-pressure cuff is inflated midway between systolic and diastolic for ~5 minutes; > 10–20 petechiae per square inch is positive, indicating capillary fragility — a simple bedside clue in dengue.

Warning Signs to Watch

• Severe abdominal pain, persistent vomiting, mucosal bleeding, lethargy/restlessness.
• Tender enlarging liver, and a rising haematocrit with a rapid drop in platelets — trigger closer monitoring/admission.

Prognosis

With timely recognition of the critical phase and careful fluid management, most children recover fully; deaths occur mainly from unrecognised plasma leakage/shock or severe bleeding — both largely preventable with monitoring.

Prevention

• Vector control — eliminate Aedes breeding sites (stored water), larvicides, personal protection.
• Community awareness; dengue vaccine only in seropositive individuals (per current guidance).