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SARS (SARS-CoV-1): Pathophysiology, Respiratory Impact & Clinical Course

Severe Acute Respiratory Syndrome (SARS) is caused by SARS-CoV-1, a betacoronavirus that emerged in 2002–2003. It primarily targets the lower respiratory tract, causing severe viral pneumonia and systemic illness.

Viral Pathogenesis in the Respiratory System

  1. Entry: Inhaled droplets/aerosols → bind ACE2 receptors on bronchial/bronchiolar epithelium, type II pneumocytes, alveolar macrophages.
  2. Replication: Robust viral replication in lower airways → direct cytopathic effect + intense host immune response.
  3. Immunopathology: "Cytokine storm" (IL-6, IL-8, IFN-γ, TNF-α, MCP-1) → massive infiltration of neutrophils, macrophages, lymphocytes → diffuse alveolar damage (DAD).
  4. Histopathology: Hyaline membranes, epithelial desquamation, edema, hemorrhage, multinucleated giant cells, organizing fibrosis (later).

Clinical Manifestations

PhaseTimingFeatures
Incubation2–7 days (max 10–14)Asymptomatic; potentially infectious late incubation
Prodrome (Week 1)Days 1–7High fever (>38°C), chills, myalgia, headache, malaise; dry cough may start
Respiratory Phase (Week 2)Days 7–14Dyspnea, hypoxemia, progressive cough; 20–30% develop ARDS requiring mechanical ventilation
Recovery / Late ComplicationsWeek 3+Improvement or progression to fibrosis, secondary infections, critical illness myopathy

Key Respiratory Complications

  • Atypical Pneumonia: Patchy/interstitial infiltrates on CXR/CT; often lower zone predominant.
  • Acute Respiratory Distress Syndrome (ARDS): Refractory hypoxemia (PaO₂/FiO₂ <300), bilateral opacities, non-cardiogenic.
  • Pulmonary Fibrosis: Long-term sequelae in survivors (reduced DLCO, restrictive pattern).
  • Secondary Bacterial/Fungal Pneumonia: Ventilator-associated, immunocompromise.

Extrapulmonary Involvement

  • GI: Watery diarrhea (viral shedding in stool; fecal-oral transmission possible).
  • Hepatic: Transaminitis.
  • Hematologic: Lymphopenia, thrombocytopenia, DIC.
  • Neurologic: Encephalitis, seizures (rare).

Diagnosis & Treatment (Historical Context)

  • Diagnosis: RT-PCR (respiratory specimens, blood, stool), serology (convalescent).
  • Treatment (2003): Supportive (O₂, ventilation, fluids), Ribavirin ± Corticosteroids (controversial, no RCT benefit), Convalescent plasma (anecdotal). No specific antiviral approved.
  • Infection Control: Strict airborne/contact precautions; superspreading events drove outbreaks.

Epidemiology & Legacy

  • 8,098 cases, 774 deaths (CFR ~9.6%) across 29 countries (2002–2003).
  • Contained via aggressive public health measures (isolation, contact tracing, quarantine, travel screening).
  • Animal reservoir: Horseshoe bats → civet cats (amplifier) → humans.
  • Laid groundwork for SARS-CoV-2 (COVID-19) response: ACE2 target, pandemic preparedness, vaccine platforms.

SARS-CoV-1 demonstrated the pandemic potential of bat-origin coronaviruses and the critical role of respiratory tropism and immune dysregulation in severe disease.

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