Cyprinid herpesvirus 3 (CyHV-3) is the etiological agent of the carp herpesvirus disease. This virus spreads very quickly in farms and causes very high mortalities, thus jeopardizing carp production in many Southern countries. This thesis proposes to study the virulence mechanisms of CyHV-3 by an evolutionary approach on the one hand. The work will focus on a recently identified viral haplotype carrying a deletion in gene 150 of CyHV-3 genome, associated with a marked attenuation of virulence. It will aim to understand the importance of this deletion in the infectious processes of this virus, the prevalence of this deletion in carp populations in Indonesia (natural and farmed), as well as the potential role of this gene in virulence. In an applied perspective, evaluate the potential of plant extracts to inhibit CyHV-3 replication in view of their use in disease prevention.