MERS-CoV: Lung Infection Mechanism, Transmission, and Clinical Features

Transmission to Lungs

1. Respiratory droplets: Cough/sneeze/talk → inhaled → attach to DPP4 receptors on lower respiratory epithelium
2. Contact/fomites: Contaminated surfaces → mucosal inoculation
3. Zoonotic: Dromedary camels → human (primary reservoir)

Pulmonary Pathogenesis

• DPP4 (CD26) highly expressed on type II pneumocytes, bronchial epithelium
• Viral entry → replication → cytopathic effect + immune dysregulation
• Cytokine storm (IL-6, IFN-γ, TNF-α) → alveolar damage, hyaline membranes
• Lymphopenia (CD4/CD8 depletion) → impaired viral clearance

Clinical Presentation

• Incubation: 2–14 days (median 5)
• Fever, cough, dyspnea (most common)
• GI: diarrhea, nausea/vomiting (~25%)
• Progression: pneumonia → ARDS → multi-organ failure
• Asymptomatic/mild cases occur (especially young, healthy)

Risk Factors for Severe Disease

• Age >50, diabetes, chronic heart/lung/kidney disease, immunosuppression, obesity
• Healthcare workers (exposure intensity)

Prevention and Control

• No vaccine licensed (candidates in development)
• Infection control: airborne + contact precautions, N95, negative pressure rooms
• Camel contact hygiene: avoid raw milk/urine, handwashing
• Travelers: avoid high-risk contacts in endemic areas (Arabian Peninsula)

Treatment

Supportive care. Remdesivir, lopinavir/ritonavir + IFN-β studied; no proven antiviral. Monoclonal antibodies in development.