H5N1 Clade 2.3.4.4b: Evolution, Global Spread, and Host Range Expansion.

Area of Science:

• Veterinary Virology
• Zoonotic Disease Epidemiology
• Molecular Evolution

Background:

• Highly pathogenic avian influenza viruses (HPAIVs) of the H5 subtype are a significant global threat to animal and public health.
• The A/goose/Guangdong/1/96 (GsGD) H5 lineage, emerging in 1996, has diversified into multiple clades, causing widespread outbreaks in poultry and wild birds.
• Global spread has been primarily observed in three clades: 2.2, 2.3.2.1, and the more recent 2.3.4.4b.

Purpose of the Study:

• To review the historical emergence and global spread of H5 HPAIVs.
• To analyze the molecular evolution of H5 HPAIVs.
• To focus on the recent expansion and mammalian spillover capacity of H5 clade 2.3.4.4b.

Main Methods:

• Literature review of scientific publications and outbreak reports.
• Analysis of epidemiological data on H5 HPAIV spread.
• Examination of molecular data related to H5 HPAIV evolution.

Main Results:

• H5 HPAIVs, particularly clade 2.3.4.4b, demonstrate continuous geographic expansion and adaptation to new environments, including Antarctica.
• Clade 2.3.4.4b has shown increasing reports of infections in various mammalian species, including companion animals, marine mammals, and livestock.
• Recent evidence of cow-to-cow and cow-to-human transmission signifies a critical shift in avian influenza epidemiology.

Conclusions:

• The H5 HPAIV clade 2.3.4.4b represents a growing concern due to its global reach and demonstrated capacity for mammalian spillover.
• The recent transmission events in cattle underscore the evolving zoonotic potential of H5 HPAIVs.
• Continued global surveillance and research are essential to monitor the evolution and spread of H5 HPAIVs and mitigate their impact on animal and public health.