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 888 H5N1 human avian influenza cases in 23 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 had spread to North America and then, in 2022, to Central and South America.
        • Sixty-seven countries reported infection with HPAI 2022 in either poultry or wild birds.
        • Also afflicts a wide variety of mammals, land- and sea-based.
      • U.S. (2022-2025): 66 human cases (as of 1/6/25) among workers related to dairy cows or poultry exposure. California and Colorado are leading in case numbers.
        • Mild disease typically, contrary to experience in SE Asia.
          • One fatality due to H5N1 in an older person with multiple comorbidities in December 2024 in Louisiana
            • Genetic analysis suggests the virus mutated within the patient, leading to a more severe illness.
          • Some cases are described without a known link to exposure (animal or infected person).
        • Considered to be low risk for human-to-human spread.
        • CDC webpage with the most up-to-date information.
  • Low pathogenic avian influenza (LPAI):
    • Occasional human infections are rarely fatal.
  • WHO has regularly updated reports from the Western Pacific region regarding HPAI and LPAI.