Discovery, Pathogenesis, and Complete Genome Characterization of Lates calcarifer Herpesvirus

In 2015 and 2016, two Barramundi (Lates calcarifer) farms in Singapore reported a disease outbreak characterized by lethargic behavior, pronounced inappetence, generalized skin lesions, erosions of the fins and tail, and ultimately high mortality in their fish. Next-generation sequencing and PCR confirmed presence of a novel virus belonging to the Alloherpesviridae family, Lates calcarifer herpesvirus (LCHV), which was subsequently isolated and cultured. We characterize, for the first time, the complete genome of two cultured LCHV isolates. The genome contains a long unique region of approximately 105,000 bp flanked by terminal repeats of approximately 24,800 bp, of which the first 8.2 kb do not show any similarity to described genomes in the Alloherpesviridae family. The two cultured isolates share 89% nucleotide identity, and their closest relatives are the viruses belonging to the genus Ictalurivirus. Experimental infections using one of the cultured LCHV isolates resulted in identical clinical signs as originally described in the index farm, both in intraperitoneal-injection infected fish and cohabitant fish, with mortality in both groups. Histopathological analysis showed pronounced abnormalities in the gills. Virus culture and PCR analysis confirmed the replication of LCHV in the infected fish, and thus Koch's postulates were fulfilled.