Genetic and Structural Factors Contributing to the Dominance and Persistence of Goose Astrovirus Type 2

Goose astrovirus (GoAstV) has emerged as a significant pathogen affecting the goose industry in China, with GoAstV-2 becoming the dominant genotype since 2017. This study explores the genetic and structural factors underlying the prevalence of GoAstV-2, focusing on codon usage bias, spike protein variability, and structural stability. Phylogenetic and effective population size analyses revealed that GoAstV-2 experienced rapid expansion between 2017 and 2018, followed by population stabilization. Codon usage analysis indicated that GoAstV-2 exhibited a weaker codon usage bias compared to GoAstV-1, suggesting greater flexibility in synonymous codon usage and potentially enhanced adaptability across host environments. Additionally, GoAstV-2's lower codon adaptation index values point to a divergence from the host’s optimal codon usage, which may reduce competition with host tRNA pools and facilitate viral replication. The spike protein of GoAstV-2 demonstrated significantly lower variability than GoAstV-1, as shown by Shannon entropy analysis, indicating greater structural stability. This stability may reduce the need for frequent mutations, allowing GoAstV-2 to persist in host populations without undergoing constant evolution. The lower antigenic variability likely decreases immune-driven selective pressure, contributing to the viral sustained transmission and long-term persistence. These findings provide new insights into the evolutionary advantages of GoAstV-2 and its epidemiological success, which could inform future control strategies aimed at mitigating its impact on poultry populations.