North American perspective on the highly pathogenic avian influenza H5Nx clade 2.3.4.4b outbreak (November 2021-March...

Area of Science:

• Veterinary Virology
• Epidemiology
• Genomics

Background:

• Highly pathogenic avian influenza (H5Nx) viruses, specifically clade 2.3.4.4b, emerged in North America in late 2021.
• This outbreak is unprecedented in its geographic spread, duration, and the range of affected hosts, including wild birds, poultry, and mammals.

Purpose of the Study:

• To provide a continental overview of the H5Nx avian influenza outbreak in North America from November 2021 to March 2025.
• To summarize surveillance findings and genomic trends.
• To inform One Health preparedness and response strategies.

Main Methods:

• Continental surveillance data collection across Canada, the United States, and Mexico.
• Genomic analysis to identify viral lineages, reassortment events, and genotypes.
• Tracking of spillover events into wild and domestic mammals.

Main Results:

• Widespread detections of H5Nx avian influenza in wild birds and poultry across North America.
• Documented spillover events into various wild and domestic mammal species.
• Identification of over 100 distinct genotypes, including recent emergence of B3.13 in cattle and D1.1 in migratory birds.

Conclusions:

• The H5Nx avian influenza outbreak demonstrates ongoing viral evolution and significant cross-species transmission risks.
• Continued surveillance and genomic monitoring are crucial for One Health preparedness.
• The findings underscore the need for robust response efforts to mitigate future outbreaks.