Polymorphism and evolution of influenza A virus genes

Area of Science:

• Virology
• Molecular Evolution
• Genetics

Background:

• Influenza A virus genes, including nonstructural protein, matrix protein, hemagglutinin, and neuraminidase, are crucial for viral function and evolution.
• Understanding the evolutionary dynamics of these genes is vital for tracking viral spread and developing interventions.

Purpose of the Study:

• To investigate the evolutionary relationships and polymorphism of key influenza A virus genes.
• To determine the mutation and substitution rates within these genes.
• To explore the factors influencing viral evolution, such as selection pressures and host species.

Main Methods:

• Compilation of nucleotide sequences from a large number of influenza A virus strains.
• Phylogenetic analysis to reconstruct evolutionary relationships.
• Estimation of mutation and nucleotide substitution rates.

Main Results:

• All investigated genes and subtypes show high polymorphism with rapid allele turnover.
• Most polymorphic sequences emerged within the last 80 years; hemagglutinin subtype divergence occurred in the last 300 years.
• A high mutation rate (0.01/nucleotide site/year) was estimated, but most genes are under purifying selection, resulting in lower substitution rates.
• Substitution rates vary among genes and are lower in nonhuman strains, potentially causing a 'freezing effect'.

Conclusions:

• Influenza A virus evolution is characterized by high mutation rates and rapid turnover of genetic variants.
• Purifying selection plays a significant role in maintaining gene integrity despite high mutation rates.
• Differences in substitution rates between human and nonhuman strains may influence viral adaptation and evolution.