As long as the culture of shrimp remains as one of the most profitable sectors in the animal food production industry, the expansion of shrimp culture to new regions and the implementation of innovative culture techniques will continue. This entails movement of shrimp stocks across regions, countries and continents. The transboundary movements of shrimp poses risk of emergence of novel viruses that will restrict shrimp production from time to time , as it has happened in shrimp farming over the past few decades.
Since 2018 unusual mortalities associated with infectious myonecrosis virus (IMNV) have been occurring in several states of Brazil. Initially, we associated these mortalities with a novel strain of IMNV. However, transcriptomic analysis showed the presence of another viral sequence in high abundance.
We characterized the novel virus using a combination of RNAseq and phylogenetic analysis, in situ hybridization, PCR, qPCR and histopathology. The full-length genome of the novel virus is ~ 10.4 kb and consist of +ssRNA genome . The genome encodes for one large open reading frame (ORF) with putative domains for a helicase, RdRp, Calicivirus coat protein, G-patch and Kinase (Figure 1A) . Phylogenetic analysis using the RdRp places the novel virus as member of the Caliciviridae. Further phylogenetic analysis using the Calicivirus coat protein show that virus does not belong to any of the know genera of the Caliciviridae .
In situ hybridization shows that the virus is localized in the nuclei of the epithelial cells of the hepatopancreas (Figure 1B ), stomach and can be observed in the lymphoid organ and muscle tissue. To our knowledge this is the only RNA virus of shrimp to infect the nuclei. We have provisionally called this virus as “Penaeus vannamei calicivirus” (PvCV ).
The Caliciviridae are well known pathogens causing a wide range of syndromes. R ecent additions to the Caliciviridae are the genera Minovirus and Salovirus that infect marine fish. The PvCV will be the most recent addition to the family. Finally, a publication is being prepared to report the diagnostic techniques to help mitigate the spread of the virus and contribute to its control.