The Features Of An Emerging Whispovirus Isolate From Freshwater Crayfish

A highly lethal freshwater crayfish Cambarus clarkii whispovirus (WSSV-Cc) was isolated from a naturally infected host. A large number of viral particles with typical nimavirus characters were observed in host cells. Genomic architecture and genetic evolution of this extremely virulent pathogen were uncovered. WSSV-Cc has a double-stranded DNA genome containing 287,179 bp, encoding 180 putative ORFs. Congruence analysis was performed between WSSV-Cc and known nimavirus genomes. The genome of WSSV-Cc is smaller than that found in isolates sampled before 2010, but is similar in size to that of recent isolates, which provided new evidence for the shrinkage of nimavirus genome size during evolution. Phylogenetic analysis with the complete genome also showed connections between genome size and evolutionary relationship. Twenty low-similarity genes and three variable regions were identified from the WSSV-Cc genome. In addition, two recombination events were detected in the WSSV-Cc genome, and analysis of the recombinant regions showed a close relationship among the three freshwater crayfish nimaviruses. These findings provide us the morphological, genomic, and genetic characters of an emerging whispovirus, which will broaden our understanding to nimaviruses and be useful for diagnosis of crayfish viral disease.