Story of an infection: viral dynamics and host responses in theCaenorhabditis elegans-Orsay virus pathosystem

SUMMARY Orsay virus (OrV) is the only known natural virus affecting Caenorhabditis elegans , with minimal impact on the worm’s fitness due to its robust innate immune response. This study aimed to understand the interactions between C. elegans and OrV by tracking the infection’s progression during larval development. Four distinct stages of infection were identified based on viral load, with a peak in capsid- encoding RNA2 coinciding with the first signs of viral egression. Transcriptomic analysis revealed temporal changes in gene expression and functions induced by the infection. A specific set of up- regulated genes remained active throughout the infection, and genes correlated and anticorrelated with virus accumulation were identified. Responses to OrV mirrored reactions to other biotic stressors, distinguishing between virus-specific responses and broader immune responses. Additionally, mutants of early response genes and defense-related processes showed altered viral load progression, uncovering new players in the antiviral defense response.