Chapter 35 - 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 (CpSBV) 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 (NSS2) equivalent of the NSS 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.