Bunyaviruses of Crustaceans

Abstract Diverse genera of bunyaviruses vectored by arthropods have evolved to infect numerous vertebrate and plant species. Viruses with bunyavirus-like virion morphology and morphogenesis characteristics also infect crustacean species. Of these, Cancer pagurus systemic bunyalike virus ( Cp SBV) of crabs and Mourilyan virus (MoV) of penaeid shrimp have been identified to possess segmented (−) ssRNA genomes, but only the genome of MoV has been sequenced. Phylogenetic analyses of the RNA-dependent RNA polymerase, envelope glycoproteins and nucleocapsid protein encoded in the L, M and S1 RNA segments, respectively, position MoV between viruses in the Phlebovirus genus of the Bunyaviridae and thrip-transmitted plant viruses in the Tenuivirus genus not yet classified formally within this family. Despite its close evolutionary relatedness to phleboviruses, the MoV genome contains a fourth RNA segment (S2) encoding a nonstructural protein (NS S2 ) equivalent of the NS S protein encoded in ambisense in the S RNA segment of phleboviruses. MoV infects Black Tiger shrimp ( Penaeus monodon ) and Kuruma shrimp ( Penaeus japonicus ) in Australia, and can cause mortality in captive-reared Penaeus japonicus . Acute infection can involve all shrimp tissues of mesodermal and ectodermal origin and be evident by extensive tissue gapping, vacuolization and spheroid development in the lymphoid organ. A genome comprising three RNA segments is currently mandatory for classification in the Bunyaviridae . However, because MoV contains more than three segments as for the plant tenuiviruses but can form ovoid-shaped enveloped virions indistinguishable from those formed by bunyaviruses, MoV might force the rigid taxonomic criteria permitting entry into the Bunyaviridae to be relaxed.