Avian Influenza

Aka: Avian Influenza, Avian Influenza A, Bird Flu, Asian H5N1, Influenza A H5N1

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II. Background

  1. Historical Avian Influenza Outbreaks
    1. Spanish Flu (H1N1): 1918-1919 (40-100 Million deaths)
    2. Asian Flu (H2N2): 1957 (2 million deaths)
    3. Hong Kong Flu (H3N2): 1968 (1 million deaths)
  2. Recent strains
    1. Asian strain (H9N2): 1998
    2. Netherlands (H7N7):2003
  3. Avian Influenza A (H5N1, Bird Flu)
    1. Currently active Avian Influenza Strain
    2. Expected to be next Influenza pandemic
    3. 1997: 18 cases (6 deaths) in Hong Kong
    4. 2004-5: 137 cases (70 deaths) Southeast Asia, China
      1. Outbreak associated with more virulent Z-strain
    5. 2006: 228 cummulative cases and 130 deaths
      1. Total cases thought to be much higher
      2. Mild cases are likely underestimated

III. Pathophysiology

  1. Life-cycle of Avian Influenza A
    1. Avian Influenza A shed in waterfowl (esp. ducks)
    2. Poultry and pigs become infected
    3. Animal handlers become infected
      1. Exposure to infected animals is primary source
      2. Human-to-human transmission requires high exposure
  2. Virulence
    1. Immune reaction to virus is intense
    2. Results in Cytokine Storm

IV. Risk Factors: Exposures

  1. Asian poultry animal handlers
  2. Asian animal markets, poultry farms, cock fights
  3. Cleaning up areas with poultry feces present
  4. Contact with fertilizer contaminated with bird feces

V. Symptoms: Onset 2-5 days after exposure

  1. Fever
  2. Cough
  3. Respiratory distress (associated with Viral Pneumonia)
  4. Watery Diarrhea

VI. Diagnosis: Pharyngeal swab for H5-Specific RNA

  1. Preferred over nasal swab
  2. Detection by Reverse transcriptase PCR

VII. Labs

  1. Complete Blood Count with Leukopenia

VIII. Imaging

  1. Chest XRay
    1. Nonspecific infiltrates by 7 days post-fever onset

IX. Management

  1. Tamiflu
    1. See Neuraminidase Inhibitors (also Relenza)
    2. Treatment: 75 mg PO bid for 5 days
      1. Must be started within 48 hours of onset
      2. Reduces illness severity by 40%
    3. Post-exposure Prophylaxis: 75 mg PO qd x7-10 days
    4. Resistance rates are currently low
  2. Other anti-viral agents
    1. Amantadine and Ramantadine resistance is high
  3. Other experimental agents
    1. Statins
      1. May reduce Cytokine Storm reaction
      2. Improves survival in Septic Shock
      3. Only effective if started prior to infection

X. Prevention

  1. Avoid exposure
    1. See Risk Factors above
  2. H5N1 Vaccine
    1. Undergoing human trials
    2. Not expected to be available for several years

XI. Resources

  1. CDC Avian Flu Information
    1. http://www.cdc.gov/flu/avian/gen-info/facts.htm
  2. WHO Avian Influenza information
    1. http://www.who.int/csr/don
  3. U.S. Department of Health and Human Services
    1. http://www.pandemicflu.gov

XII. References

  1. Fauci (2006) Emerg Infect Dis 12:73-7 [PubMed]
  2. Juckett (2006) Am Fam Physician 74(5):783-90 [PubMed]
  3. Monto (2005) N Engl J Med 352:323-5 [PubMed]

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