Taxonomy of the order Mononegavirales: update 2019.

In February 2019, following the annual taxon ratification vote, the order Mononegavirales was amended by the addition of four new subfamilies and 12 new genera and the creation of 28 novel species. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV)

2020 taxonomic update for phylum Negarnaviricota (Riboviria: Orthornavirae), including the large orders Bunyavirales and Mononegavirales.

In March 2020, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. At the genus rank, 20 new genera were added, two were deleted, one was moved, and three were renamed. At the species rank, 160 species were added, four were deleted, ten were moved and renamed, and 30 species were renamed. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV

The occurrence, pathology and morphological development of Paranucleospora theridion in salmon louse (Lepeophtheirus salmonis)

In 2003 a microsporidian parasite was discovered in salmon lice (Lepeophtheirus salmonis). The same parasite was later described from Atlantic salmon (Salmo salar) and salmon lice and was identified as Paranucleospora theridion. P. theridion is associated with disease in both salmon lice and Atlantic salmon. In the present study Real-time RT-PCR has been used to study the prevalence and intensity of P. theridion in the developmental stages of salmon lice. Light microscopy and electron microscopy has been used to study the pathology and morphological development of P.theridion in salmon lice. The present study shows that the salmon lice are infected with P. theridion in the first chalimus stage and that a prevalence of 100% is reached before the free-moving first preadult stage. This indicates that the lice get infected while feeding on P. theridion infected epithelial cells of Atlantic salmon. The intensity of P. theridion in salmon lice development increases from chalimus stage 1 until the preadult stages are reached. This show that there is a proliferation of P. theridion during the salmon lice development. A drop in intensity in adult lice may be explained by the death of heavily infected lice. Registrations of prevalence of medium to heavy P. theridion infected salmon based on visual examination showed that the prevalence is highest in winter and that the development of P. theridion may be temperature dependent. Morphological studies of P. theridion development in salmon lice indicates sexual reproduction based on the presence of synaptonemal complexes, loss of nuclear membrane and the alteration between diplokaryotic and monokaryotic nuclei. A hypothesis including cytoplasmic fusion of meronts, mitotic division of diplokarya and the fusion of monokarya resulting in diploid monokarya has been suggested. Virus-like particles, a unicellular organism and bacteria associated with pathology in salmon lice were observed during microscopical examination of the development of P. theridion. In addition a potentially new species of Udonella were observed during examination of the presence of P. theridion in Caligus centrodonti

Genomic characterization and phylogenetic position of two new species in Rhabdoviridae infecting the parasitic copepod, salmon louse (Lepeophtheirus salmonis)

Several new viruses have emerged during farming of salmonids in the North Atlantic causing large losses to the industry. Still the blood feeding copepod parasite, Lepeophtheirus salmonis, remains the major challenge for the industry. Histological examinations of this parasite have revealed the presence of several virus-like particles including some with morphologies similar to rhabdoviruses. This study is the first description of the genome and target tissues of two new species of rhabdoviruses associated with pathology in the salmon louse. Salmon lice were collected at different Atlantic salmon (Salmo salar) farming sites on the west coast of Norway and prepared for histology, transmission electron microscopy and Illumina sequencing of the complete RNA extracted from these lice. The nearly complete genomes, around 11 600 nucleotides encoding the five typical rhabdovirus genes N, P, M, G and L, of two new species were obtained. The genome sequences, the putative protein sequences, and predicted transcription strategies for the two viruses are presented. Phylogenetic analyses of the putative N and L proteins indicated closest similarity to the Sigmavirus/Dimarhabdoviruses cluster, however, the genomes of both new viruses are significantly diverged with no close affinity to any of the existing rhabdovirus genera. In situ hybridization, targeting the N protein genes, showed that the viruses were present in the same glandular tissues as the observed rhabdovirus-like particles. Both viruses were present in all developmental stages of the salmon louse, and associated with necrosis of glandular tissues in adult lice. As the two viruses were present in eggs and free-living planktonic stages of the salmon louse vertical, transmission of the viruses are suggested. The tissues of the lice host, Atlantic salmon, with the exception of skin at the attachment site for the salmon louse chalimi stages, were negative for these two viruses

Adult female salmon lice, <i>Lepeophtheirus salmonis</i> (arrow), feeding on Atlantic salmon (A).

<p>An area of reduced transparency (ring) in the cephalothorax in the vicinity of the second antenna (sa) adult lice (B). Mouth tubule (mt).</p

Percent amino acid identity of Ls9 and Ls127 L protein domains and subdomains compared with a selection of related rhabdoviruses.

<p><i>Vesiculovirus</i> (VSV  =  Vesicular stomatitis virus (ABP01784)), <i>Sprivivirus</i> (SVCV  =  Spring viraemia of carp virus (ABW24037) and PFRV  =  Pike fry rhabdovirus (ACP28002)), <i>Perhabdovirus</i> (PRV  =  Perch rhabdovirus (AFX72892)), <i>Ephemerovirus</i> (BEFV  =  Bovine ephemeral fever virus (NP065409)), <i>Sigmavirus</i> (Sigma  =  Sigma virus (AFV52407)), <i>Tibrovirus</i> (TIBV  =  Tibrogargan virus (YP007641376)), <i>Tupavirus</i> (DURV  =  <i>Durham virus</i> (ADB88761)). Unassigned (SMRV  =  Turbot rhabdovirus (ADU05406), WONV  =  Wongabel virus (YP002333280), NGAV  =  Ngaingan virus (YP003518294), MOUV  =  Moussa virus (ACZ81407), KOLEV  =  Kolente virus (AHB08865)).</p><p>Percent amino acid identity of Ls9 and Ls127 L protein domains and subdomains compared with a selection of related rhabdoviruses.</p

Multinucleated (nu) gland cells with channels containing virus-like particles (arrows) and amorphic material (A and B).

<p>C) This figure shows viroplasm (vp) in the vicinity of a channel containing virus-like particles (arrow). Note the accumulation of electron dense material (arrow head) on the inside of the cell membrane. Nucleus (nu).</p