PATHOGENS

• Categorized according to the ability to kill chickens in a laboratory setting:
  • Highly pathogenic avian influenza (HPAI):
    • Influenza (H5N1), avian first detected in Chinese geese in 1996
    • Occasional human pathogen since 1997
      • Since 2003, the WHO has reported 860 H5N1 human avian influenza cases in 19 countries (mostly SE Asia), with a mortality rate of ~50%.
      • H5 avian influenza infection in man from Colorado (CDC, April 2022) with direct poultry exposure; extensive avian influenza among poultry flocks and wild birds in N. America in 2021-2022.
      • Since 2020, H5 clade 2.3.4.4b variants have caused considerable deaths among wild birds and poultry, striking countries in Africa, Asia and Europe. By 2021, it spread to North America and then in 2022, to Central and South America.
        • 67 countries reported infection with HPAI in 2022 in either poultry or wild birds.
  • Low pathogenic avian influenza (LPAI):
    • Most influenza A H5 types (except H5N1 as above)
      • H5N6 may be an exception; WHO has 36 cases reported in 2021, with 21 deaths.
    • Most influenza A H7 types
      • H7N9 (2013-14, 2016-17 China) appears to cause severe human infection (mortality rate ~40%).
      • Types H7N2, H7N3, and H7N7 cause mild-moderate occasional human infection
    • H9N2 (rare human illness, mild), 100 people since 1998, predominantly SE Asia, Egypt, the Arabian peninsula, India, Pakistan and Senegal.
    • H6: one human infection in Taiwan (2013)
    • H10: three occurrences since 2004 in humans (Egypt, Australia, China)