Evaluation of white spot syndrome virus genome stability across serial passages

White spot syndrome virus (WSSV) is a major threat to shrimp aquaculture worldwide. WSSV has a broad host range, and its evolutionary dynamics during passage from one host to another remain poorly understood. The goal of this study was to investigate how the transition from one species to another could potentially affect genome stability. To this end, two WSSV isolates originating from Japan (OK01) and Thailand (SK1) were subjected to inter- and intra-species serial passages in two species of shrimp and one crab species in order to examine changes in viral loads and viral genomes. The WSSV genome remained highly stable after serial passaging. SNPs constituted the majority of genomic variants detected across all WSSV isolates. These results highlight strong purifying selection to preserve core functions. Nevertheless, mutation and evolutionary mechanisms differed between the OK01 and the SK1 inoculated groups. Recombination analysis of the OK01 inoculated group points to a more adaptable genome that changes dynamically in response to cross-host passages. The structural, regulatory, and replication functions were enriched under positive selection, suggesting these genes play a crucial role in host interaction and pathogenicity. This study demonstrates that WSSV evolution exhibits a compromise between genomic stability and adaptive flexibility: Same-host maintenance maintains stability, whereas cross-host transmission expedites the generation of genetic diversity.