Dengue Fever

Acute febrile illness caused by dengue virus (DENV, family Flaviviridae, 4 serotypes DENV-1–4), transmitted by Aedes aegypti (and Aedes albopictus) mosquitoes. Infection with one serotype confers lifelong immunity to that serotype but only transient cross-protection to others; secondary infection with a different serotype carries higher risk of severe dengue (antibody-dependent enhancement).

Classified by WHO 2009 criteria:

• Dengue without warning signs

• Dengue with warning signs: abdominal pain, persistent vomiting, fluid accumulation (ascites, pleural effusion), mucosal bleeding, lethargy/restlessness, liver enlargement >2cm, rising hematocrit with rapid platelet drop

• Severe dengue: severe plasma leakage (shock, fluid accumulation with respiratory distress), severe bleeding, or severe organ impairment (liver, CNS, heart)

Phases of illness: febrile phase (days 1–3) → critical phase (days 4–6, plasma leakage risk) → recovery phase (days 7+, fluid reabsorption).

• Febrile phase: sudden high fever (39–40°C), severe headache, retro-orbital pain, myalgia, arthralgia ("breakbone fever"), maculopapular/morbilliform rash, mild hemorrhagic manifestations (petechiae, positive tourniquet test), nausea/vomiting, facial flushing

• Critical phase (around defervescence, days 4–6: the dangerous transition): temperature drops but this does NOT mean improvement, plasma leakage begins here

• Warning signs (monitor closely, admit if present): abdominal pain/tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy/restlessness, liver enlargement, rising hematocrit concurrent with rapid platelet decline

• Progression to severe dengue: narrow pulse pressure (<20mmHg), tachycardia, cold clammy extremities, delayed capillary refill (signs of dengue shock syndrome), significant bleeding (GI, vaginal, intracranial), organ impairment (AST/ALT ≥1000, impaired consciousness, cardiac involvement)

• Recovery phase: gradual reabsorption of extravasated fluid, improved appetite, bradycardia, characteristic convalescent rash ("isles of white in a sea of red")

• Red flags for shock: restlessness/irritability progressing to lethargy, cold extremities, prolonged capillary refill >2sec, weak/rapid pulse, narrowing pulse pressure, precede hypotension, which is a LATE sign

• Clinical suspicion: acute febrile illness + 2 of (nausea/vomiting, rash, aches/pains, positive tourniquet test, leukopenia, warning signs) in endemic area/exposure

• FBC: leukopenia, thrombocytopenia (progressive fall, nadir typically around critical phase), rising hematocrit (hemoconcentration, indicates plasma leakage; a 20% rise from baseline is significant)

• NS1 antigen: positive from day 1–7 of fever (early detection)

• IgM/IgG serology: IgM detectable from day 5 onward (acute infection); IgG rise in secondary infection (paired sera useful)

• PCR: confirms serotype, most sensitive in first 5 days

• LFTs: transaminitis common; AST/ALT elevation

• Coagulation profile if bleeding/severe disease: prolonged PT/APTT, low fibrinogen in severe cases

• Serial hematocrit and platelet monitoring: essential for detecting critical phase transition

• Ultrasound/CXR: detect subclinical plasma leakage (pleural effusion, ascites, gallbladder wall thickening), useful in risk-stratifying warning-sign patients

Differentials: malaria (always test/exclude in endemic overlap areas), chikungunya, zika, typhoid, leptospirosis, measles, rubella, other viral hemorrhagic fevers, influenza.

No specific antiviral; management is supportive, centered on careful fluid management and monitoring for plasma leakage/shock.

Dengue without warning signs (outpatient management):

• Adequate oral fluid intake (oral rehydration solution, fruit juice, avoid excessive plain water)

• Paracetamol for fever/pain: strictly avoid NSAIDs (ibuprofen, aspirin, diclofenac) and other salicylates: bleeding risk and Reye's syndrome

• Daily review: temperature, fluid intake/output, warning signs, FBC (hematocrit, platelets)

• Educate on warning signs requiring immediate return

Dengue with warning signs (admit for monitoring):

• IV isotonic crystalloids (normal saline or Ringer's lactate) starting at 5–7mL/kg/hour, titrate based on clinical response, hematocrit, urine output

• Monitor vitals, urine output, hematocrit every 4–6 hours during critical phase

• Reduce IV rate as patient stabilizes/enters recovery phase (risk of fluid overload once leakage resolves, this is a common cause of iatrogenic harm if fluids not tapered)

Severe dengue/dengue shock syndrome (ICU-level care):

• Aggressive fluid resuscitation: IV crystalloid bolus 10–20mL/kg over 1 hour, reassess; consider colloids (e.g., dextran) if repeated boluses fail

• Blood transfusion if significant hemorrhage (whole blood or packed cells); platelet transfusion NOT routinely indicated for thrombocytopenia alone without active bleeding, even very low counts (<10,000-20,000) are managed expectantly unless bleeding present

• Correct hypoglycemia, electrolyte imbalances, metabolic acidosis

• Manage organ-specific complications (hepatic failure, encephalopathy, myocarditis) supportively

• Avoid IM injections and unnecessary invasive procedures (bleeding risk)

Discharge criteria: afebrile ≥24 hours without antipyretics, improved appetite, stable hematocrit, platelet count rising (>50,000), no respiratory distress, adequate urine output.

Prevention: vector control (eliminate breeding sites, insecticide-treated nets, repellents), dengue vaccine (CYD-TDV/Dengvaxia, only for seropositive individuals due to ADE risk in seronegative recipients; TAK-003/Qdenga, broader use profile, check local guidelines).