Dengue Fever and Pulmonary Disease — Comprehensive Review (15 Marks)

1. Introduction

2. Etiology and Epidemiology

3. Pathophysiology

Core Mechanisms:

1. Viral replication in monocytes/macrophages, dendritic cells → release of TNF-α, IL-6, IL-8, IFN-γ
2. Antibody-Dependent Enhancement (ADE): Pre-existing non-neutralizing antibodies from prior serotype enhance viral uptake by Fc-receptor-bearing cells → massive cytokine storm in secondary infection
3. Capillary leak syndrome: Cytokines (especially C3a, C5a, VEGF, NS1 protein) disrupt endothelial tight junctions → plasma leakage into third spaces (pleural cavity, peritoneum, pericardium)
4. Thrombocytopenia: Immune-mediated platelet destruction + suppressed megakaryopoiesis → bleeding tendency
5. NS1 protein activates TLR4 → endothelial glycocalyx disruption → vascular permeability

4. WHO 2009 Classification (Revised)

Dengue
├── Dengue Without Warning Signs
├── Dengue With Warning Signs*
└── Severe Dengue
    ├── Severe plasma leakage → Dengue Shock Syndrome (DSS)
    ├── Severe bleeding
    └── Severe organ impairment (liver, CNS, heart, kidney, LUNGS)

• Abdominal pain or tenderness
• Persistent vomiting
• Clinical fluid accumulation (pleural effusion, ascites)
• Mucosal bleeding
• Lethargy / restlessness
• Liver enlargement >2 cm
• Rapidly rising HCT with rapid platelet fall

5. Clinical Phases of Dengue

6. Pulmonary Manifestations of Dengue — Core Focus

6.1 Spectrum of Pulmonary Disease

6.2 Pleural Effusion

• Most common pulmonary complication
• Predominantly right-sided (due to hepatomegaly + perihepatic capillary leak); can be bilateral
• Exudative in nature (protein-rich plasma leaked)
• Clinically: Dyspnea, reduced breath sounds, stony dullness on percussion
• CXR/USG: Blunting of costophrenic angle, meniscus sign
• Management: Observation; reabsorbed spontaneously during recovery. Thoracocentesis only if causing respiratory compromise

6.3 Pulmonary Edema

• Two types:
  1. Non-cardiogenic (capillary leak) — predominant mechanism; cytokine-mediated endothelial injury → fluid into alveoli
  2. Cardiogenic — myocarditis, dengue-induced cardiac dysfunction (rare)
• CXR: Bilateral fluffy/alveolar opacities, Kerley B lines, enlarged cardiac silhouette
• Management: Fluid restriction, diuretics during recovery phase; cautious fluid resuscitation

6.4 ARDS in Dengue

• Defined by: Acute onset hypoxia (PaO₂/FiO₂ <300), bilateral infiltrates on CXR, non-cardiogenic origin (Berlin Definition)
• Dengue ARDS triggers:
  • Direct alveolar damage by DENV
  • Massive cytokine storm (TNF-α, IL-6, IL-8)
  • Immune complex deposition in alveolar capillaries
  • Iatrogenic fluid overload during resuscitation
• Clinical Features: Acute-onset dyspnea, progressive hypoxemia, diffuse bilateral crackles, refractory to O₂
• CXR/CT: Bilateral ground-glass opacities, consolidation, "white-out" lungs in severe ARDS
• Mortality: 20–50% in dengue ARDS

ARDS Management in Dengue:

1. Lung-protective ventilation: Tidal volume 6 ml/kg IBW; plateau pressure <30 cmH₂O
2. PEEP titration (FiO₂/PEEP table)
3. Prone positioning if PaO₂/FiO₂ <150
4. Fluid conservative strategy after initial resuscitation
5. Treat underlying dengue — no specific antivirals; supportive care
6. Corticosteroids: Not routinely recommended in dengue ARDS; controversial

6.5 Dengue Pneumonitis

• Direct viral infection of lung parenchyma
• Clinically resembles atypical pneumonia: Fever, cough, exertional dyspnea, hypoxia
• CXR: Patchy interstitial infiltrates
• BAL: May show lymphocytic alveolitis; viral RNA detectable
• Must be differentiated from bacterial superinfection
• Treatment: Supportive; no specific antivirals

6.6 Pulmonary Hemorrhage

• Rare but life-threatening
• Due to severe thrombocytopenia (platelets <10,000/μL) + DIC
• Presents as: Massive hemoptysis, blood-tinged endotracheal secretions, rapidly falling Hb
• CXR: Dense unilateral or bilateral opacities (blood-filled alveoli)
• Management: Platelet transfusion (target >50,000 for active bleed), FFP for coagulopathy, intubation if massive

7. Chest X-Ray in Dengue — Key Findings

8. Diagnosis

Laboratory Diagnosis

Investigations for Pulmonary Assessment

• Chest X-ray: First-line; detects effusion, edema, infiltrates
• HRCT Chest: Ground-glass opacities, consolidation, interlobular septal thickening
• Pulse oximetry / ABG: PaO₂/FiO₂ ratio for ARDS classification
• Bedside USG: Rapidly detects pleural effusion (>95% sensitivity)
• Echocardiography: Rule out cardiogenic cause; detect pericardial effusion

9. Differential Diagnosis of Pulmonary Involvement

10. Management

A. General Principles

• No specific antiviral therapy — management is entirely supportive
• Three-group WHO triage:
  • Group A: Outpatient (no warning signs, able to tolerate orals)
  • Group B: In-hospital (warning signs, comorbidities)
  • Group C: ICU (severe dengue — DSS, ARDS, severe bleeding, organ failure)

B. Fluid Management (Critical)

⚠️ Key Exam Point: Fluid overload during the recovery phase (Days 7–10) is the most common iatrogenic cause of pulmonary edema in dengue. Plasma is reabsorbed from third spaces → intravascular overload → pulmonary edema.

C. Respiratory Management

• Supplemental O₂ for SpO₂ <94%
• High-flow nasal cannula (HFNC) for moderate hypoxemia
• NIV / Intubation for ARDS (PaO₂/FiO₂ <200)
• Lung-protective ventilation: TV 6 ml/kg, Pplat <30, PEEP titrated
• Prone positioning for severe ARDS (PaO₂/FiO₂ <150 for >12 hours)

D. Specific Interventions

E. Drugs to AVOID

• Aspirin / NSAIDs — increase bleeding risk
• Antibiotics — not for uncomplicated dengue
• Corticosteroids — not proven beneficial; may increase viral replication
• IM injections — hematoma risk with thrombocytopenia

11. Complications Summary

12. Prognosis

• Uncomplicated dengue: Self-limiting, mortality <1%
• Dengue with ARDS: Mortality 20–50%
• DSS: Mortality <1% with adequate management; up to 10–40% if untreated
• Poor prognostic markers: Fluid overload, ARDS, pulmonary hemorrhage, myocarditis, elevated liver enzymes, prolonged shock

13. Prevention

• Dengvaxia (CYD-TDV): Licensed; only for seropositive individuals ≥9 years; risk of severe disease in seronegative recipients
• TAK-003 (Qdenga): Newer vaccine; approved in some countries; effective against all 4 serotypes
• Vector control: Source reduction (eliminate standing water), larviciding, insecticide spraying
• Personal protection: Repellents (DEET), long-sleeved clothing, mosquito nets

14. Key Exam Points (High-Yield Summary)

1. Most common pulmonary complication = Pleural effusion (right-sided)
2. Most dangerous pulmonary complication = ARDS / Pulmonary hemorrhage
3. Mechanism of lung injury = Capillary leak (cytokine-mediated endothelial damage) + fluid overload in recovery
4. NS1 antigen = earliest serological marker (Days 1–5)
5. Critical phase = Days 4–6 (defervescence phase) — most pulmonary complications occur here
6. Avoid NSAIDs/aspirin — worsens bleeding
7. Fluid restriction in recovery phase = prevents iatrogenic pulmonary edema
8. ARDS management = Lung-protective ventilation (TV 6 ml/kg, Pplat <30 cmH₂O)
9. Platelet transfusion threshold = <10,000/μL (prophylactic) or active hemorrhage regardless of count
10. Dengvaxia risk: Contraindicated in seronegative individuals — increases risk of severe dengue