Dengue Fever

🦟 Dengue virus is a mosquito-borne flavivirus spread by Aedes aegypti and Aedes albopictus. First infection usually causes Dengue fever, while a second infection with a different serotype can cause the more severe and potentially fatal Dengue haemorrhagic fever (DHF) / Dengue shock syndrome (DSS).

📖 About

• Viral haemorrhagic fever caused by a flavivirus.
• Spread by Aedes aegypti and Aedes albopictus mosquitoes.
• Endemic in Asia, Pacific, Americas, and parts of Africa.
• Incubation period: ~5 days.

🌍 Spread

• Transmitted by mosquito bites 🦟 (peak biting after dawn and before sunset).
• DHF/DSS occurs mostly in endemic regions of Asia, Pacific Islands, Cuba, and the Americas.
• Person-to-person spread does not occur.

🧬 Aetiology

• Four serotypes: DEN-1, DEN-2, DEN-3, DEN-4.
• Secondary infection with a different serotype → higher risk of DHF/DSS due to antibody-dependent enhancement.
• Immune activation → cytokine release (TNF, IFN-γ) → ↑ vascular permeability → shock.
• A person may be infected up to four times in a lifetime.

🩺 Clinical Assessment

• Suspect in: travel/living in endemic area + acute febrile illness.
• Plus ≥2 features:
  • 🌡️ Nausea/vomiting
  • 🌸 Rash (erythematous, “islands of white in a sea of red”)
  • ⚡ Retro-orbital pain, joint pains, headache
  • 🔎 Leucopenia
  • Positive tourniquet test
• ⚠️ Warning signs (require admission):
  • Severe abdominal pain/tenderness
  • Persistent vomiting
  • Mucosal bleed
  • Hepatomegaly > 2 cm
  • Fluid accumulation (ascites, pleural effusion)
  • Lethargy/restlessness
  • Rise in HCT + fall in platelets
• Symptoms worst day 1–5 → small number deteriorate in “critical phase” as fever resolves.

💉 Dengue Haemorrhagic Fever / Dengue Shock Syndrome

• Occurs on reinfection with a different serotype.
• Features:
  • Bleeding: petechiae, GI bleed, mucosal bleed
  • Shock: hypotension, narrow pulse pressure, cyanosis
  • Restlessness, lethargy
  • Platelets < 100 × 10⁹/L
• Mortality < 1% in good centres.

👶 At Risk of DHF/DSS

• Children < 12 years.
• Females > Males.
• Whites > Blacks.
• Well-nourished > Malnourished.
• Serotype 2 most dangerous.

🧾 Differential Diagnosis

• Always consider malaria (but malaria typically has no rash).

🔬 Investigations

• FBC: low WCC, thrombocytopenia.
• DHF: high haematocrit (haemoconcentration).
• Serology: 4-fold ↑ in IgG titres.
• PCR: dengue RNA detection.

🛡️ Prevention

• 🦟 Mosquito control: eliminate breeding sites, use repellents, protective clothing.
• 💉 Dengue vaccine (Dengvaxia): approved in the US for children 9–16 years with prior confirmed dengue infection, in endemic regions.

💊 Management

• No specific antiviral therapy. Supportive only.
• Outpatient: if no warning signs → paracetamol, fluids, rest, monitor closely.
• Admit: warning signs, extremes of age, pregnancy, diabetes, renal failure, social concerns.
• Severe dengue: emergency.
  • IV fluids (minimal volume required) – switch to oral ASAP.
  • Platelet transfusion only if < 10 × 10⁹/L or active bleeding.
  • Blood transfusion if haematocrit falling + unstable.
  • Colloids (albumin) if refractory shock.
  • Strict monitoring: NEWS 4-hourly, HCT 6–12 hourly, urine output 8–12 hourly.
  • Capillary leak syndrome may cause pleural/pericardial effusion, ascites – usually resolves by day 7.
• ⚠️ Avoid: aspirin, NSAIDs, steroids, unnecessary fluids.

📌 Key Exam Pearls

• Critical period = after fever settles → risk of rapid deterioration.
• Secondary infection (different serotype) → DHF/DSS due to antibody-dependent enhancement.
• Diagnosis: fever + travel + leucopenia + thrombocytopenia ± rash.
• Mortality < 1% with supportive care.

📚 References

• CDC Dengue Cheat Sheet
• CDC Dengue Overview