David M. Stone

Taxonomy of the order Mononegavirales: update 2016

In 2016, the order Mononegavirales was emended through the addition of two new families (Mymonaviridae and Sunviridae), the elevation of the paramyxoviral subfamily Pneumovirinae to family status (Pneumoviridae), the addition of five free-floating genera (Anphevirus, Arlivirus, Chengtivirus, Crustavirus, and Wastrivirus), and several other changes at the genus and species levels. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

Nucleotide sequence of the glycoprotein gene of viral haemorrhagic septicaemia (VHS) viruses from different geographical areas: a link between VHS in farmed fish species and viruses isolated from North Sea cod (Gadus morhua L.)

RT-PCR methods have been applied to the detection and sequencing of the glycoprotein gene of viral haemorrhagic septicaemia virus (VHSV), the rhabdovirus which causes viral haemorrhagic septicaemia (VHS) in farmed salmonid fish. Phylogenetic analysis of a 360 nt region of the glycoprotein gene from a range of marine and fresh water VHSV isolates identified three genogroups, I-III. Significantly, two virus isolates recovered from ulcerated North Sea cod caught off the Shetland Islands, and an isolate recovered from diseased turbot farmed on the island of Gigha, Scotland were assigned to the same genogroup. Moreover, a virus isolated from diseased turbot farmed on the Baltic Sea coast shared 99.4% nucleotide sequence similarity with a virus associated with a VHS outbreak in rainbow trout. This is the first time that a genetic link between a VHS outbreak and natural VHSV infections of marine fish species has been demonstrated.

Microsporidia: diverse, dynamic, and emergent pathogens in aquatic systems

Microsporidia cause important diseases in aquatic organisms. Susceptible hosts span a remarkable taxonomic spectrum, from protists to mammals. Known genera represent a small fraction of extant taxa in global aquatic systems. Transmitting horizontally or vertically, effects range from cryptic to catastrophic; individual level effects being extrapolated to populations and ecosystems. Debate over positioning within the eukaryotes and internal structuring of the phylum has benefited from molecular phylogenetic approaches to taxonomy. Similar tools offer new perspectives on transmission between hosts of differing trophic status and habitats. Accessible models for host-pathogen interaction are emerging from full genome sequencing projects. Hyperparasitism and the close phylogenetic relationship between taxa infecting invertebrates and vertebrates not only underline a ubiquity in aquatic systems but also potential for zoonotic transfer.

First Report of Spring Viremia of Carp Virus (SVCV) in Wild Common Carp in North America

Abstract In spring 2002, an estimated 1,500 common carp Cyprinus carpio in Cedar Lake, northwestern Wisconsin, died over a 6-week period from late April through the first week in June. Three moribund carp were necropsied and had signs consistent with spring viremia of carp (SVC) disease, including petechiae and ecchymotic hemorrhages on the skin, ascites, and edematous kidney and spleen. A virus was isolated on fathead minnow cells and shown to be a rhabdovirus by electron microscopy. Immunoassay results indicated a close serological relationship with spring viremia of carp virus (SVCV). This was confirmed by a reverse transcriptase–polymerase chain reaction assay and subsequent analysis of a subsection glycoprotein gene. Immunocytochemistry and serum neutralization tests indicated that the Cedar Lake isolate did not share complete antigenic identity with the European reference SVCV. Also, the isolate showed an inhibition of cytopathic effect after repeated subculture in epithelioma papulosum cyprini and ...

Hepatospora eriocheir (Wang and Chen, 2007) gen. et comb. nov. infecting invasive Chinese mitten crabs (Eriocheir sinensis) in Europe.

We describe a microsporidian parasite infecting non-native Chinese mitten crabs (Eriochier sinensis) from Europe. Electron microscopy revealed merogonic and sporogonic life stages bound within a plasmalemma. The crab parasite develops polar tube precursors at the sporont stage but does not complete formation of the intact spore extrusion apparatus at the stage of the sporogonial plasmodium like Enterocytozoon bienuesi and other representatives of the Enterocytozoonidae. Its presence within an aquatic crustacean host, and a distinct molecular phylogeny based on partial small subunit ribosomal RNA (SSU rRNA) gene sequences also place it relatively close, though distinct to, existing genera within the Enterocytozoonidae. Consideration of morphological and phylogenetic characteristics of other hepatopancreas-infecting microsporidia from crustaceans suggests that certain ones (e.g. Enterospora canceri) are retained within the clade corresponding to the existing family Enterocytozoonidae, while others, including the parasite described here, may eventually be grouped in a sister taxon potentially of family rank. Based upon morphological and host similarity, it is likely that the parasite described here is the same as Endoreticulatus eriocheir (Wang and Chen, 2007), previously described from Chinese mitten crabs in Asia. However, using a combined taxonomic approach based upon morphological and phylogenetic data, we propose the formation of a new genus (Hepatospora) to replace the previous generic classification of the Asian parasite as Endoreticulatus. The microsporidian from the hepatopancreas of E. sinensis is named Hepatospora eriocheir (Wang and Chen, 2007) gen. et comb. nov. It is assumed that the parasite was introduced during initial invasions of this crab to Europe during the early 20th Century.

Mikrocytids Are a Broadly Distributed and Divergent Radiation of Parasites in Aquatic Invertebrates

Microcell parasites have independently evolved in several eukaryotic lineages and are increasingly recognized as important and emerging pathogens of diverse hosts, including species of economic importance subject to international legislation concerning the trading of aquatic animals [1-3]. The microcell Mikrocytos mackini causes Denman Island disease of oysters and represents one of the most genetically divergent eukaryotes known. Mikrocytos has remained an isolated lineage with a limited distribution. We investigated two emerging diseases of juvenile crabs and oysters from the UK using massively parallel sequencing and targeted primer approaches to reveal that their causative agents are highly divergent lineages related to M. mackini (Paramikrocytos canceri n. gen. et n. sp. and M. mimicus sp. nov., respectively). We demonstrate a major new globally distributed parasite radiation (Mikrocytida ord. nov.) with phylogenetic affinities to the commercially important haplosporidian parasites of invertebrates. Mikrocytids have eluded detection because of their small size, intracellular habit, and extreme sequence divergence. P. canceri was frequently detected in a range of shoreline invertebrates, demonstrating that these newly recognized parasites are in fact common, diverse, and widespread and should be considered when assessing the risks of aquaculture activities, invasive species spread, and movements of ballast water and sediments with associated invertebrates.

The first report of viral haemorrhagic septicaemia in farmed rainbow trout, Oncorhynchus mykiss (Walbaum), in the United Kingdom.

Viral haemorrhagic septicaemia (VHS) was diagnosed in rainbow trout in the UK in May 2006. VHS virus (VHSV) was isolated from fingerlings showing typical histopathological lesions at a single rainbow trout farm site experiencing high mortality. The virus was confirmed as VHSV by serological and molecular biological tests. Phylogenetic analysis based on the complete glycoprotein gene sequence revealed that the isolate was closely related (99% nucleotide identity) to several Danish isolates from 1991 to 2000 and was assigned to VHSV genogroup Ia. The pathogenicity of the isolate was determined in infection experiments using rainbow trout fry. Following waterborne challenge, cumulative mortalities reached 96.67-100% by 12 days post-infection. This represents the first isolation of a pathogenic freshwater VHSV in the UK.

Identification of Microsatellite Repeats in Turbot (Scophthalmus maximus) and Dover Sole (Solea solea) using a RAPD-Based Technique: Characterization of Microsatellite Markers in Dover Sole.

Abstract: We have used a RAPD-based technique to identify several microsatellite repeats in turbot (Scophthalmus maximus) and Dover sole (Solea solea) and report the characterization of six novel polymorphic microsatellite markers for Dover sole. These are the first such markers to be developed for this flatfish species. They exhibit much higher levels of heterozygosity than those previously observed with allozyme loci and should prove useful in addressing population genetic questions as well as more fundamental aquaculture-related questions.

Sphaerothecum destruens pathology in cyprinids

Sphaerothecum destruens is a significant intracellular parasite of fish which has caused disease and mortalities in cultured north American Chinook salmon Oncorhynchus tshawytscha and Atlantic salmon Salmo salar. Several hosts for S. destruens have been identified within the Salmonidae family, and the histopathology of the infection can differ between hosts. Recently, S. destruens has been associated with the most invasive cyprinid species in Europe, topmouth gudgeon Pseudorasbora parva. Accurate disease identification based on thorough descriptions of clinical signs and histopathology in this new range of hosts is thus paramount to support further epizootiological studies. In this study, the associated histopathology of S. destruens infection is described along with its pathogenesis in the endangered cyprinid sunbleak Leucaspius delineatus. Histological examination of 100 L. delineatus in a wild population in the south of England revealed the presence of S. destruens infections, with a prevalence of 5% with S. destruens, suggesting an over-dispersed distribution within the L. delineatus sample. Clinical signs of the infection were absent, but histological examination revealed the presence of both disseminated and nodular lesions in several organs.

Plastic parasites: Extreme dimorphism creates a taxonomic conundrum in the phylum Microsporidia

In this paper, we combine field observations of highly statistically significant co-occurrence with histopathological, ultrastructural and molecular phylogenetic analyses, to provide evidence for extreme morphological plasticity in a microsporidium parasite infecting the musculature of marine crabs. The parasite appears to alternate between lineages that culminate in production of either bizarre needle-like spores in the peripheral sarcoplasm of heart and skeletal muscle fibres (reminiscent of Nadelspora canceri infecting Cancer magister) or alternatively, Ameson-like spores with pronounced surface projections, in the skeletal muscles (as for Ameson pulvis, previously described infecting Carcinus maenas). Both lineages occur in direct contact with the cytoplasm of host muscle cells and can exist simultaneously within the same cell. Pathological data appears to reveal a remarkable shift in morphology during pathogenic remodelling of host tissues. Sequence analysis of multiple clones derived from amplification of the ssrRNA gene from infected regions of the heart and skeletal muscles appear to confirm the genetic identity of the two lineages. Furthermore, derived ssrRNA gene sequences are more similar (>99%) to N. canceri than to the coparasite Ameson michaelis infecting Callinectes sapidus (93%). Although molecular phylogenetic data support transfer of A. pulvis into the genus Nadelspora, the expansion in the generic description required to include such widely divergent characteristics is so significant as to be unfeasible within the current taxonomic framework of the phylum Microsporidia. At present, it is preferable to propose that the parasite infecting C. maenas forms a clade with other morphologically diverse but phylogenetically and ecologically similar muscle-infecting microsporidians from marine crustacean hosts. Given the strong evidence for significant plasticity in morphology amongst members of the phylum Microsporidia, novel approaches to phylogeny, based predominantly upon the informed use of molecular sequence data, are now deemed a necessity.