H5N1 is a highly pathogenic avian influenza A virus. Human infections are rare but severe, with a case fatality rate around 50%. No sustained human-to-human transmission has been documented.
Transmission
- Primary: Direct or indirect contact with infected poultry (live markets, farming, slaughtering).
- Exposure: Feathers, feces, respiratory secretions, contaminated surfaces.
- Rare: Prolonged close contact with infected human (household clusters).
- Not foodborne: Properly cooked poultry and eggs are safe.
Clinical Presentation
- Incubation: 2–8 days (up to 17).
- Rapid onset: High fever (>38°C), cough, dyspnea.
- Lower respiratory predominance: Primary viral pneumonia (bilateral infiltrates).
- GI symptoms: Diarrhea, vomiting, abdominal pain (more common than seasonal flu).
- Complications: ARDS, multi-organ failure, encephalitis, secondary bacterial pneumonia.
Diagnosis
- RT-PCR (nasopharyngeal, throat, lower respiratory) – specific for H5.
- Viral culture (BSL-3+).
- Serology (paired acute/convalescent).
Treatment
- Oseltamivir (Tamiflu): 75 mg BID × 5 days (adults); start ASAP (ideally <48 hrs); higher dose/longer course considered for severe cases.
- Baloxavir: Single dose; active against some resistant strains.
- Supportive: Oxygen, ventilation (ARDS protocols), vasopressors, renal replacement.
- Corticosteroids: Not routinely recommended (prolonged shedding, secondary infection risk).
- Antibiotics: For bacterial superinfection.
Prevention
- Poultry workers: PPE, seasonal flu vaccination (prevents reassortment).
- Travelers: Avoid live markets, undercooked poultry, bird contact.
- Surveillance: WHO GISRS, OFFLU network.
- Pandemic preparedness: Candidate vaccine viruses (CVVs) updated; stockpiled antivirals.
