A new study published in the journal Nature has shed light on the global surge of highly pathogenic avian influenza (HPAI) H5N1 since 2021. The research provides insights into the ecological and virological dynamics of the virus and offers guidance for more effective mitigation strategies moving forward.
Background:
Influenza A viruses, belonging to the Alphainfluenzavirus genus and Orthomyxoviridae family, are categorized based on the antigenic properties of their surface proteins. While low-pathogenic strains primarily affect wild aquatic birds, high-pathogenic strains, specifically subtypes H5 and H7, emerge through mutations that enable severe infections in poultry.
These highly pathogenic strains, especially the H5N1 subtype, have caused major outbreaks, often controlled through culling. The viruses evolve rapidly, exchanging genetic material with less severe strains, resulting in widespread transmission across continents. Recent escalations in wild bird outbreaks, particularly by the H5N2, H5N6, and H5N8 viruses (collectively known as H5Nx), have raised concerns about their evolving virulence and adaptability, highlighting the importance of continuous surveillance and understanding of their evolutionary dynamics.
The study:
The researchers compiled highly pathogenic avian influenza H5 genomes, specifically those containing the Hemagglutinin (HA) gene, along with sample data such as collection date, location, and host species, from the Global Initiative on Sharing Avian Influenza Data (GISAID) and National Center for Biotechnology Information (NCBI) databases. The genomes were classified according to the World Health Organization (WHO) H5N1 nomenclature system.
Analysis of the genomes divided them into subclades based on their phylogenetic relationships to WHO H5 candidate vaccine viruses. The researchers also identified the hosts as either domestic or wild birds using strain names, metadata, and original publications, ensuring accuracy in location coordinates.
Various analyses were conducted, including phylogenetic analyses, reassortment analyses, and Bayesian evolutionary inference, to unravel the origins and evolutionary pathways of the HPAI H5Nx viruses and understand their spatial diffusion and host transmission patterns.
Study findings:
Since 2005, there have been concerning trends in the recurrence of HPAI H5 viruses among wild and domestic birds, with outbreaks expanding from Asia and Africa to Europe and North America. The major outbreaks have been primarily caused by clades 2.3.4.4 and 2.3.4.4b, with strains like H5N8 and H5N6 causing significant epidemics.
Genomic analyses have revealed the intricate origins and evolutions of these viruses. For instance, recent outbreaks can be traced back to separate viral lineages in China, indicating regional evolution despite limited surveillance. Genetic reassortment among European strains has led to the emergence of virulent forms responsible for the outbreaks in 2021 and 2022.
The global trajectory of the HPAI H5Nx viruses, particularly the clade 2.3.4.4b H5N8 strain, has been systematic and persistent. Migration patterns of the virus from Egypt to Russia and Eastern Europe, followed by spread across Eurasia and China, have contributed to new reassortments and human H5N6 infections.
The study also highlighted the critical role of wild birds in the long-distance propagation of HPAI H5 viruses and emphasized the need for vigilant surveillance and proactive measures to manage future outbreaks.
Implications and recommendations:
Understanding the dynamics of highly pathogenic avian influenza H5N1 and other H5Nx viruses is essential for effectively managing and mitigating future outbreaks. Regional issues can quickly escalate into global crises, highlighting the interconnectedness of the world and the importance of robust reporting and proactive measures.
Continued surveillance, comprehensive reporting, and collaborative efforts between countries and regions are crucial in preventing and controlling the spread of these viruses. By studying the evolutionary dynamics and transmission patterns, scientists and health authorities can develop more effective strategies for mitigating the impact of highly pathogenic avian influenza outbreaks on both animal and human health.
*Note:
- Source: Coherent Market Insights, Public sources, Desk research
- We have leveraged AI tools to mine information and compile it
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