The episodic resurgence of highly pathogenic avian influenza H5 virus

Abstract

Highly pathogenic avian influenza (HPAI) H5N1 activity has intensified globally since 2021, replacing the dominant clade 2.3.4.4 H5N8 virus. H5N1 viruses have spread rapidly to four continents, causing increasing reports of mass mortality in wild birds and poultry. The ecological and virological properties required for future mitigation strategies are unclear. Using epidemiological, spatial and genomic approaches, we demonstrate changes in the source of resurgent H5 HPAI and reveal significant shifts in virus ecology and evolution. Outbreak data indicates key resurgent events in 2016/17 and 2020/21 leading up to the panzootic spread of H5N1 in 2021/22, with increases in virus diffusion velocity and greater persistence in wild birds. Genomic analysis shows that the 2016/17 epizootics originated in Asia, where HPAI H5 reservoirs are well documented as persistent. However, in 2020/21, 2.3.4.4b H5N8 viruses emerged in domestic poultry in Africa containing several novel mutations altering the HA structure, receptor binding, and antigenicity. The new H5N1 virus emerged from H5N8 through reassortment in wild birds along the Adriatic flyway around the Mediterranean Sea, and was characterized by extensive reassortment with low pathogenic avian influenza in domestic and wild birds as they spread globally. In contrast, earlier outbreaks of H5N8 were caused by a more stable genetic constellation, revealing dynamic changes in HPAI H5 genomic evolution. These results suggest a shift in the epicenter of HPAI H5 beyond Asia to new regions in Africa, the Middle East, Europe, and North and South America. The persistence of HPAI H5 with resurgence potential in domestic birds indicates that elimination strategies remain a high priority.

Avian influenza virus cross‐infections as test case for pandemic preparedness: From epidemiological hazard models to sequence‐based early viral warning systems

“…An international consortium of virologists reconstructed the path of HPAI H5 infections using epidemiological, geographical and genomic approaches (Xie et al., 2023). Over the last two decades, the HPAI H5 gene has split into 10 phylogenetic clades with clade 2 being the most prominent.…”

Transmission of lethal H5N1 clade 2.3.4.4b avian influenza in ferrets

“…Since then, the Gs/Gd lineage H5 viruses have evolved and spread significantly since their emergence, and their classification, based on the H5 protein, includes up to 10 phylogenetic clades 1,2 . Clade 2 viruses, more specifically, H5 HA lineage 2.3.4.4, including H5N2, H5N6, and H5N8 have predominated globally since their spread out of Asia in 2014, with H5N8 viruses causing the majority of infections from 2014-2020, including outbreaks that occurred in North America 3 . In 2020, clade 2.3.4.4b viruses spread to parts of Asia, Africa, and Europe via migratory birds, and in the autumn of 2021, H5N1 viruses were detected in North America in wild and domestic birds.…”

No evidence for HPAI H5N1 2.3.4.4b incursion into Australia in 2022

“…The current high pathogenicity avian influenza (HPAI) H5 panzootic is having a profound impact on the poultry industry and wildlife (1). While lineage 2.3.4.4b is of current concern, HPAI H5 emerged in poultry in 1996 and has caused outbreaks in wild bird populations episodically since 2005 (2). The epidemiology of this virus has changed substantially with the emergence of new lineages, as exampled by Clade 2 viruses which caused the first wild bird mass mortality event at Qinghai Lake, China in 2005 (3).…”

“…The epidemiology of this virus has changed substantially with the emergence of new lineages, as exampled by Clade 2 viruses which caused the first wild bird mass mortality event at Qinghai Lake, China in 2005 (3). A novel lineage emerged in 2014 (2.3.4.4), which has diversified and caused substantial mortality, including mass mortality events, of wild birds in 2014, 2016, 2020-present, along with ongoing outbreaks in poultry in Eurasia and North America (2).…”