Predicting the evolution of human influenza A.

Area of Science:

• Virology
• Molecular Evolution
• Immunology

Background:

• Influenza A subtype H3 viruses constantly evolve due to antigenic drift.
• Understanding the genetic basis of viral evolution is crucial for public health.
• Hemagglutinin (HA) is a key surface protein involved in viral entry and is a target for the immune system.

Purpose of the Study:

• To identify specific codons under positive selection in the HA1 domain of H3 influenza A viruses.
• To assess the predictive value of mutations in these codons for future viral lineage emergence.
• To investigate the association of positively selected codons with functionally important sites.

Main Methods:

• Analysis of human influenza A H3 hemagglutinin gene sequences.
• Application of positive selection detection methods to identify specific codons.
• Retrospective analysis correlating mutations in selected codons with the emergence of future viral lineages.
• Mapping of selected codons to antibody binding sites and receptor binding sites.

Main Results:

• Eighteen codons in the HA1 domain were identified as being under positive selection.
• Viral lineages with the most mutations in these codons were progenitors of future H3 lineages in 9 out of 11 seasons.
• Positively selected codons were frequently located in antibody combining sites (A or B) or the sialic acid receptor binding site.
• Not all codons within these functionally important sites demonstrated predictive value.

Conclusions:

• Specific positively selected codons in HA1 are strong indicators of future H3 influenza A virus evolution.
• Monitoring these key codons in newly isolated H3 strains can aid in predicting viral fitness and emergence.
• This approach may enhance surveillance strategies for identifying pandemic-prone influenza strains during antigenic drift.