Virus discovery in cultured portunid crabs: Genomic, phylogenetic, histopathological and microscopic characterization of a reovirus and a new bunyavirus

Abstract

Portunid crabs are distributed worldwide and highly valued in aquaculture. Viral infections are the main limiting factor for the survival of these animals and, consequently, for the success of commercial-scale cultivation. However, there is still a lack of knowledge about the viruses that infect cultured portunid crabs worldwide. Herein, the genome sequence and phylogeny of Callinectes sapidus reovirus 2 (CsRV2) are described, and the discovery of a new bunyavirus in Callinectes danae cultured in southern Brazil is reported. The CsRV2 genome sequence consists of 12 dsRNA segments (20,909 nt) encode 13 proteins. The predicted RNA-dependent RNA polymerase (RdRp) shows a high level of similarity with that of Eriocheir sinensis reovirus 905, suggesting that CsRV2 belongs to the genus Cardoreovirus. The CsRV2 particles are icosahedral, measuring approximately 65 nm in diameter, and exhibit typical non-turreted reovirus morphology. High throughput sequencing data revealed the presence of an additional putative virus genome similar to bunyavirus, called Callinectes danae Portunibunyavirus 1 (CdPBV1). The CdPBV1 genome is tripartite, consisting of 6,654 nt, 3,120 nt and 1,656 nt single-stranded RNA segments that each encode a single protein. Each segment has a high identity with European shore crab virus 1, suggesting that CdPBV1 is a new representative of the family Cruliviridae. The putative spherical particles of CdPBV1 measure ∼120 nm in diameter and present a typical bunyavirus morphology. The results of the histopathological analysis suggest that these new viruses can affect the health and, consequently, the survival of C. danae in captivity. Therefore, the findings reported here should be used to improve prophylactic and pathogen control practices and contribute to the development and optimization of the production of soft-shell crabs on a commercial scale in Brazil.