Amarilloviruses of Aquatic Animals

The family Flaviviridae has been expanded to include the highly divergent flavi-like viruses into three new families, Flaviviridae, Pestiviridae, and Hepaciviridae in the order Amarillovirales. Classical flavivirids are small, enveloped viruses with positive-sense ssRNA genomes lacking a 3’ poly(A) tail, and ~ 9.0-13.0 kb in length, with a single ORF encoding structural proteins at the N terminus and nonstructural proteins at the C terminus. Members infect a wide range of mammals, birds, and insects, and many are host-specific and pathogenic. Although the RdRP gene sequences of the flavi-like viruses group phylogenetically with those of classical flavivirids, flavi-like viruses often encode larger polyproteins and possess substantially longer genomes of up to ~ 40 kb, and some have a 3’ poly(A) tail. Their host range extends across the whole animal kingdom and in angiosperm plants. This review describes the reported flavi-like viruses of aquatic animals, providing a meaningful update on all three new families in Amarillovirales that have been discovered in fish, crustaceans, mollusks, and echinoderms, using metagenomics. These amarilloviruses include pathogenic viruses of aquatic animals, such as Cyclopterus lumpus virus (CLuV) detected in moribund lumpfish, and Infectious precocity virus (IPV) found in iron prawn syndrome (IPS)-affected farmed giant freshwater prawns.