Novel infectious Myonecrosis virus (IMNV) variant is associated with recent disease outbreaks in Penaeus vannamei shrimp in Brazil

Infectious myonecrosis virus (IMNV) has impacted the sustainable growth of shrimp aquaculture in Brazil and other shrimp farming nations around the globe. This virus contains a non-segmented dsRNA of ~8.2 kbp and has been tentatively assigned to the family Totiviridae . In recent years in Brazil (2016 to 2021), unusual mortalities that do not follow the normal course of infection described for IMNV have been observed in several states (Pará, Maranhão, Piaui, Ceará, Rio Grande do Norte, Alagoas, Sergipe and Bahia). Moribund animals are tested PCR positive and histological examination reveals the characteristic lesions caused by IMNV. In this study, we used Next Generation Sequencing to determine the complete genome of a novel IMNV strain (Br-1) from the state of Ceara from the 2018 culture cycle associated with unusually high mortalities. The full-length genome of Br-1 is 8185 bp and shows 97.94% identity to the reference strain. Sequence comparison using the RdRp region and phylogenetic analysis using the full-length genome of Br-1 revealed that this strain is more closely related with IMNV strains from Indonesia rather than strains from Brazil. These findings suggest a potential movement of animals between shrimp farming regions and underscores the importance to enforce stricter testing measures to reduce the risk of spreading lethal pathogens that could compromise the sustainability of shrimp aquaculture worldwide. • The full-length genome of a novel variant of infectious myonecrosis virus (IMNV) associated with increased mortality in shrimp aquaculture in Brazil was characterized • The IMNV variant appears to be more closely related to strains from Indonesia • These finding suggest potential movement of animals between shrimp farming countries