Isolations of the Spring Viremia of Carp Virus in the Upper Mississippi River (USA), Including a New Host, the Quillback.

In July of 2018 and 2019, wild fish health surveys were conducted along the Wisconsin and Minnesota portions of the upper Mississippi River. Spring viremia of carp virus (SVCV) was isolated from Common Carp Cyprinus carpio as well as a newly identified host species, the Quillback Carpiodes cyprinus. Sanger sequencing of the gene encoding for the G protein revealed a high similarity of the Quillback isolate to various SVCV isolates identified from Common Carp that were collected during earlier wild fish health surveys and mortality events in the USA.

Development of duplex qPCR targeting Carnobacterium maltaromaticum and Vagococcus salmoninarum.

In November 2018, Vagococcus salmoninarum was identified as the causative agent of a chronic coldwater streptococcosis epizootic in broodstock brook trout (Salvelinus fontinalis) at the Iron River National Fish Hatchery in Wisconsin, USA. By February 2019, the epizootic spread to adjacent raceways containing broodstock lake trout (Salvelinus namaycush), whereby fish were found to be coinfected with Carnobacterium maltaromaticum and V. salmoninarum.

Vagococcus salmoninarum I-A chronic coldwater streptococcosis in broodstock brook trout (Salvelinus fontinalis) in Wisconsin, USA.

In 2018, Vagococcus salmoninarum was isolated from two lots of broodstock "coaster" brook trout (Salvelinus fontinalis) containing ~1,500 fish at the Iron River National Fish Hatchery, at which time it was identified as the causative agent of a chronic coldwater streptococcosis epizootic. Clinical signs included exophthalmia, lethargy, erratic swimming and loss of equilibrium. Female fish experienced disproportionately higher morbidity and mortality than male co-inhabitants, and routinely retained eggs following spawning.

Vagococcus salmoninarum II-qPCR, tropism and egg-associated transmission.

Vagococcus salmoninarum was identified as the causative agent of a chronic epizootic in broodstock "coaster" brook trout (Salvelinus fontinalis) at the Iron River National Fish Hatchery. The epizootic spanned more than a year, was unresponsive to multiple florfenicol treatments, and resulted in >50% mortality of the affected fish. The decision was made to cull the remaining fish during spawning, which presented an opportunity to more thoroughly examine V.

Genomic characterization of a novel calicivirus, FHMCV-2012, from baitfish in the USA.

During regulatory sampling of fathead minnows (Pimephales promelas), a novel calicivirus was isolated from homogenates of kidney and spleen inoculated into bluegill fry (BF-2) cells. Infected cell cultures exhibiting cytopathic effects were screened by PCR-based methods for selected fish viral pathogens. Illumina HiSeq next generation sequencing of the total RNA revealed a novel calicivirus genome that showed limited protein sequence similarity to known homologs in a BLASTp search.

Novel reovirus associated with epidemic mortality in wild largemouth bass (Micropterus salmoides).

Reoviruses (family Reoviridae) infect vertebrate and invertebrate hosts with clinical effects ranging from inapparent to lethal. Here, we describe the discovery and characterization of Largemouth bass reovirus (LMBRV), found during investigation of a mortality event in wild largemouth bass (Micropterus salmoides) in 2015 in WI, USA. LMBRV has spherical virions of approximately 80 nm diameter containing 10 segments of linear dsRNA, aligning it with members of the genus Orthoreovirus, which infect mammals and birds, rather than members of the genus Aquareovirus, which contain 11 segments and infect teleost fishes.

Development and evaluation of reverse transcription loop-mediated isothermal amplification assay for the detection of the fathead minnow nidovirus.

Fathead minnow nidovirus (FHMNV) is a serious baitfish-pathogenic virus in North America. Studies to trace the spread of the virus and determine its host range are hampered by the absence of reliable diagnostic assays. In this study, a one-step, reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed that targets a region in the FHMNV spike protein gene.

Isolation and molecular characterization of a novel picornavirus from baitfish in the USA.

During both regulatory and routine surveillance sampling of baitfish from the states of Illinois, Minnesota, Montana, and Wisconsin, USA, isolates (n = 20) of a previously unknown picornavirus were obtained from kidney/spleen or entire viscera of fathead minnows (Pimephales promelas) and brassy minnows (Hybognathus hankinsoni). Following the appearance of a diffuse cytopathic effect, examination of cell culture supernatant by negative contrast electron microscopy revealed the presence of small, round virus particles (∼ 30-32 nm), with picornavirus-like morphology. Amplification and sequence analysis of viral RNA identified the agent as a novel member of the Picornaviridae family, tentatively named fathead minnow picornavirus (FHMPV).